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Research involving Lowell Observatory staff 2012
(Articles and chapters)

This is a work ever in progress.

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Years: 2012 Bottom

    2012

  1. Oszkiewicz, D., Muinonen, K., Virtanen, J., Granvik, M., Bowell, E., 2012, P&SS, 73, 30, Modeling collision probability for Earth-impactor 2008 TC3
    We study the evolution of the Earth collision probability of asteroid 2008 TC3 using a short observational arc and small numbers of observations. To assess impact probability, we use techniques that rely on the orbital-element probability density function characterized using both Markov-chain Monte-Carlo orbital ranging and Monte-Carlo ranging. First, we evaluate the orbital uncertainties for the object from the night of discovery onwards and examine the collapse of the orbital-element distributions in time. Second, we examine the sensitivity of the results to the assumed astrometric noise. Each of the orbits obtained from the MCMC ranging method is propagated into the future (within chosen time bounds of the expected impact), and the collision probability is calculated as a weighted fraction of the orbits leading to a collision from the Earth. We compare the results obtained with both methods.
  2. Crockett, C., Mahmud, N., Prato, L., Johns-Krull, C., Jaffe, D., Hartigan, P., Beichman, C., 2012, ApJ, 761, 164, A Search for Giant Planet Companions to T Tauri Stars
    We present results from an ongoing multiwavelength radial velocity (RV) survey of the Taurus-Auriga star-forming region as part of our effort to identify pre-main-sequence giant planet hosts. These 1-3 Myr old T Tauri stars present significant challenges to traditional RV surveys. The presence of strong magnetic fields gives rise to large, cool star spots. These spots introduce significant RV jitter which can mimic the velocity modulation from a planet-mass companion. To distinguish between spot-induced and planet-induced RV modulation, we conduct observations at ~6700 A and ~2.3 m and measure the wavelength dependence (if any) in the RV amplitude. CSHELL observations of the known exoplanet host Gl 86 demonstrate our ability to detect not only hot Jupiters in the near-infrared but also secular trends from more distant companions. Observations of nine very young stars reveal a typical reduction in RV amplitude at the longer wavelengths by a factor of ~2-3. While we cannot confirm the presence of planets in this sample, three targets show different periodicities in the two wavelength regions. This suggests different physical mechanisms underlying the optical and the K-band variability.
  3. Martinez-Galarza, J., Hunter, D., Groves, B., Brandl, B., 2012, ApJ, 761, 3, Ongoing Massive Star Formation in NGC 604
    NGC 604 is the second most massive H II region in the Local Group, thus an important laboratory for massive star formation. Using a combination of observational and analytical tools that include Spitzer spectroscopy, Herschel photometry, Chandra imaging, and Bayesian spectral energy distribution fitting, we investigate the physical conditions in NGC 604 and quantify the amount of massive star formation currently taking place. We derive an average age of 4 1 Myr and a total stellar mass of 1.6+1.6 - 1.0 105 M for the entire region, in agreement with previous optical studies. Across the region, we find an effect of the X-ray field on both the abundance of aromatic molecules and the [Si II] emission. Within NGC 604, we identify several individual bright infrared sources with diameters of about 15 pc and luminosity-weighted masses between 103 M and 104 M . Their spectral properties indicate that some of these sources are embedded clusters in process of formation, which together account for ~8% of the total stellar mass in the NGC 604 system. The variations of the radiation field strength across NGC 604 are consistent with a sequential star formation scenario, with at least two bursts in the last few million years. Our results indicate that massive star formation in NGC 604 is still ongoing, likely triggered by the earlier bursts.
  4. Crossfield, I., Barman, T., Hansen, B., Tanaka, I., Kodama, T., 2012, ApJ, 760, 140, Re-evaluating WASP-12b: Strong Emission at 2.315 m, Deeper Occultations, and an Isothermal Atmosphere
    We revisit the atmospheric properties of the extremely hot Jupiter WASP-12b in light of several new developments. First, we present new narrowband (2.315 m) secondary eclipse photometry, which exhibits a planet/star flux ratio of 0.45% 0.06%, corresponding to a brightness temperature of 3640 230 K; second, recent Spitzer/Infrared Array Camera and Hubble Space Telescope/Wide Field Camera 3 observations; and third, a recently observed star only 1'' from WASP-12, which has diluted previous observations and which we further characterize here. We correct past WASP-12b eclipse measurements for the presence of this object, and we revisit the interpretation of WASP-12b's dilution-corrected emission spectrum. The resulting planetary emission spectrum is well approximated by a blackbody, and consequently our primary conclusion is that the planet's infrared photosphere is nearly isothermal. Thus, secondary eclipse spectroscopy is relatively ill suited to constrain WASP-12b's atmospheric abundances, and transmission spectroscopy may be necessary to achieve this goal.
  5. Neugent, K., Massey, P., Morrell, N., 2012, AJ, 144, 162, The Discovery of a Rare WO-type Wolf-Rayet Star in the Large Magellanic Cloud
    While observing OB stars within the most crowded regions of the Large Magellanic Cloud, we happened upon a new Wolf-Rayet (WR) star in Lucke-Hodge 41, the rich OB association that contains S Doradus and numerous other massive stars. At first glance the spectrum resembled that of a WC4 star, but closer examination showed strong O VI 3811, 34 lines, leading us to classify it as a WO4. This is only the second known WO in the LMC, and the first known WO4 (the other being a WO3). This rarity is to be expected due to these stars' short lifespans as they represent the most advanced evolutionary stage in a massive star's lifetime before exploding as supernovae. This discovery shows that while the majority of WRs within the LMC have been discovered, there may be a few WRs left to be found.

    This paper includes data gathered with the 6.5 m Magellan Telescope located at Las Campanas Observatory, Chile.

  6. Hunter, D., Ficut-Vicas, D., Ashley, T., Brinks, E., Cigan, P., Elmegreen, B., Heesen, V., Herrmann, K., Johnson, M., Oh, S., Rupen, M., Schruba, A., Simpson, C., Walter, F., Westpfahl, D., Young, L., Zhang, H., 2012, AJ, 144, 134, Little Things
    We present LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey), which is aimed at determining what drives star formation in dwarf galaxies. This is a multi-wavelength survey of 37 dwarf irregular and 4 blue compact dwarf galaxies that is centered around H I-line data obtained with the National Radio Astronomy Observatory (NRAO) Very Large Array (VLA). The H I-line data are characterized by high sensitivity (<=1.1 mJy beam-1 per channel), high spectral resolution (<=2.6 km s-1), and high angular resolution (~6''). The LITTLE THINGS sample contains dwarf galaxies that are relatively nearby (<=10.3 Mpc; 6'' is <=300 pc), that were known to contain atomic hydrogen, the fuel for star formation, and that cover a large range in dwarf galactic properties. We describe our VLA data acquisition, calibration, and mapping procedures, as well as H I map characteristics, and show channel maps, moment maps, velocity-flux profiles, and surface gas density profiles. In addition to the H I data we have GALEX UV and ground-based UBV and H images for most of the galaxies, and JHK images for some. Spitzer mid-IR images are available for many of the galaxies as well. These data sets are available online.
  7. Johnson, M., Hunter, D., Oh, S., Zhang, H., Elmegreen, B., Brinks, E., Tollerud, E., Herrmann, K., 2012, AJ, 144, 152, The Stellar and Gas Kinematics of the LITTLE THINGS Dwarf Irregular Galaxy NGC 1569
    In order to understand the formation and evolution of Magellanic-type dwarf irregular (dIm) galaxies, one needs to understand their three-dimensional structure. We present measurements of the stellar velocity dispersion in NGC 1569, a nearby post-starburst dIm galaxy. The stellar vertical velocity dispersion, z, coupled with the maximum rotational velocity derived from H I observations, V max, gives a measure of how kinematically hot the galaxy is, and, therefore, indicates its structure. We conclude that the stars in NGC 1569 are in a thick disk with a V max/z = 2.4 0.7. In addition to the structure, we analyze the ionized gas kinematics from O III observations along the morphological major axis. These data show evidence for outflow from the inner starburst region and a potential expanding shell near supermassive star cluster (SSC) A. When compared to the stellar kinematics, the velocity dispersion of the stars increases in the region of SSC A supporting the hypothesis of an expanding shell. The stellar kinematics closely follow the motion of the gas. Analysis of high-resolution H I data clearly reveals the presence of an H I cloud that appears to be impacting the eastern edge of NGC 1569. Also, an ultra-dense H I cloud can be seen extending to the west of the impacting H I cloud. This dense cloud is likely the remains of a dense H I bridge that extended through what is now the central starburst area. The impacting H I cloud was the catalyst for the starburst, thus turning the dense gas into stars over a short timescale, ~1 Gyr. We performed a careful study of the spectral energy distribution using infrared, optical, and ultraviolet photometry, producing a state-of-the-art mass model for the stellar disk. This mass modeling shows that stars dominate the gravitational potential in the inner 1 kpc. The dynamical mass of NGC 1569, derived from V max, shows that the disk may be dark matter deficient in the inner region, although, when compared to the expected virial mass determined from halo abundance matching techniques, the dark matter profile seems to agree with the observed mass profile at a radius of 2.2 kpc.
  8. Knight, M., Schleicher, D., Farnham, T., Schwieterman, E., Christensen, S., 2012, AJ, 144, 153, A Quarter-century of Observations of Comet 10P/Tempel 2 at Lowell Observatory: Continued Spin-down, Coma Morphology, Production Rates, and Numerical Modeling
    We report on photometry and imaging of Comet 10P/Tempel 2 obtained at Lowell Observatory from 1983 through 2011. We measured a nucleus rotation period of 8.950 0.002 hr from 16 nights of imaging acquired between 2010 September and 2011 January. This rotation period is longer than the period we previously measured in 1999, which was itself longer than the period measured in 1988, and demonstrates that Tempel 2 is continuing to spin down, presumably due to torques caused by asymmetric outgassing. A nearly linear jet was observed which varied little during a rotation cycle in both R and CN images acquired during the 1999 and 2010 apparitions. We measured the projected direction of this jet throughout the two apparitions and, under the assumption that the source region of the jet was near the comet's pole, determined a rotational pole direction of R.A./decl. = 151/+59 from CN measurements and R.A./decl. = 173/+57 from dust measurements (we estimate a circular uncertainty of 3 for CN and 4 for dust). Different combinations of effects likely bias both gas and dust solutions and we elected to average these solutions for a final pole direction of R.A./decl. = 162 11/+58 1. Photoelectric photometry was acquired on 3 nights in 1983, 2 nights in 1988, 19 nights in 1999/2000, and 10 nights in 2010/2011. The activity exhibited a steep "turn-on" ~3 months prior to perihelion (the exact timing of which varies) and a relatively smooth decline after perihelion. The activity during the 1999 and 2010 apparitions was similar; limited data in 1983 and 1988 (along with IUE data from the literature) were systematically higher and the difference cannot be explained entirely by the smaller perihelion distance. We measured a "typical" composition, in agreement with previous investigators. Monte Carlo numerical modeling with our pole solution best replicated the observed coma morphology for a source region located near a comet latitude of +80 and having a radius of ~10. Our model reproduced the seasonal changes in activity, suggesting that the majority of Tempel 2's activity originates from a small active region located near the pole. We also find that a cosine-squared solar angle function gives the best fit as compared to a standard cosine function.
  9. Neugent, K., Massey, P., Georgy, C., 2012, ApJ, 759, 11, The Wolf-Rayet Content of M31
    Wolf-Rayet (WR) stars are evolved massive stars, and the relative number of WC-type and WN-type WRs should vary with the metallicity of the host galaxy, providing a sensitive test of stellar evolutionary theory. However, past studies of the WR content of M31 have been biased toward detecting WC stars, as their emission-line signatures are much stronger than those of WNs. Here, we present the results of a survey covering all of M31's optical disk (2.2 deg2), with sufficient sensitivity to detect the weaker-lined WN types. We identify 107 newly found WR stars, mostly of WN type. This brings the total number of spectroscopically confirmed WRs in M31 to 154, a number we argue is complete to ~95%, except in regions of unusually high reddening. This number is consistent with what we expect from the integrated H luminosity compared to that of M33. The majority of these WRs formed in OB associations around the Population I ring, although 5% are truly isolated. Both the relative number of WC- to WN-type stars as well as the WC subtype distribution suggest that most WRs exist in environments with higher-than-solar metallicities, which is consistent with studies of M31's metallicity. Although the WC to WN ratio we find for M31 is much lower than that found by previous studies, it is still higher than what the Geneva evolutionary models predict. This may suggest that Roche-lobe overflow produces the excess of WC stars observed at high metallicity, or that the assumed rotational velocities in the models are too high.

    The spectroscopic observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. MMT telescope time was granted by NOAO, through the Telescope System Instrumentation Program (TSIP). TSIP is funded by the National Science Foundation. This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory.

  10. Boyajian, T., von Braun, K., van Belle, G., McAlister, H., ten Brummelaar, T., Kane, S., Muirhead, P., Jones, J., White, R., Schaefer, G., Ciardi, D., Henry, T., Lopez-Morales, M., Ridgway, S., Gies, D., Jao, W., Rojas-Ayala, B., Parks, J., Sturmann, L., Sturmann, J., Turner, N., Farrington, C., Goldfinger, P., Berger, D., 2012, ApJ, 757, 112, Stellar Diameters and Temperatures. II. Main-sequence K- and M-stars
    We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for ~K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to ~2%, ~5%, and ~4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by ~3%, and underestimate the radii of stars with radii <0.7 R by ~5%. These conclusions additionally suggest that the models over account for the effects that the stellar metallicity may have on the astrophysical properties of an object. By comparing the interferometrically measured radii for the single star population to those of eclipsing binaries, we find that for a given mass, single and binary star radii are indistinguishable. However, we also find that for a given radius, the literature temperatures for binary stars are systematically lower compared to our interferometrically derived temperatures of single stars by ~200 to 300 K. The nature of this offset is dependent on the validation of binary star temperatures, where bringing all measurements to a uniform and correctly calibrated temperature scale is needed to identify any influence stellar activity may have on the physical properties of a star. Lastly, we present an empirically determined H-R diagram using fundamental properties presented here in combination with those in Boyajian et al. for a total of 74 nearby, main-sequence, A- to M-type stars, and define regions of habitability for the potential existence of sub-stellar mass companions in each system.
  11. Lebouteiller, V., Sloan, G., Groenewegen, M., Matsuura, M., Riebel, D., Whelan, D., Bernard-Salas, J., Massey, P., Bayet, E., 2012, A&A, 546, A94, Oxygen-rich dust production in IC 10
    Context. We report the detection of oxygen-rich circumstellar envelopes in stars of the nearby (700 kpc) starburst galaxy IC 10. The star-formation history and the chemical environment of this galaxy make it an ideal target to observe dust production by massive stars in a metal-poor environment.
    Aims: The goal of this study is to identify oxygen-rich stars in IC 10 and to constrain their nature between asymptotic giant branch stars (AGBs), red supergiants (RSGs), and other bright infrared sources. We examine the mass-loss rates of the stars and compare to results obtained for the Magellanic Clouds. Our objectives are to (1) assess whether RSGs can be significant dust producers in IC 10, and (2), solve the discrepancy between the star-formation history of IC 10 and the relatively low number of RSGs detected in the optical.
    Methods: We search for silicate dust in emission by using the spectral map observed with the Infrared Spectrograph on board the Spitzer Space Telescope. The optical (UBVRI) and infrared (JHK, Spitzer/IRAC and Spitzer/MIPS) photometry are used to assert the membership of the stars to IC 10 and distinguish between AGBs and RSGs. Radiative models are used to infer mass-loss rates and stellar luminosities.
    Results: The luminosity and colors of at least 9 silicate emission sources are consistent with stars within IC 10. Furthermore, the photometry of 2 of these sources is consistent with RSGs. We derive dust mass-loss rates similar to the values found in the Magellanic Clouds. Accounting for the sample completeness, RSGs are not important contributors to the dust mass budget in IC 10.

    Appendix A is available in electronic form at http://www.aanda.org

  12. Christophe, B., Spilker, L., Anderson, J., Andre, N., Asmar, S., Aurnou, J., Banfield, D., Barucci, A., Bertolami, O., Bingham, R., Brown, P., Cecconi, B., Courty, J., Dittus, H., Fletcher, L., Foulon, B., Francisco, F., Gil, P., Glassmeier, K., Grundy, W., Hansen, C., Helbert, J., Helled, R., Hussmann, H., Lamine, B., Lammerzahl, C., Lamy, L., Lehoucq, R., Lenoir, B., Levy, A., Orton, G., Paramos, J., Poncy, J., Postberg, F., Progrebenko, S., Reh, K., Reynaud, S., Robert, C., Samain, E., Saur, J., Sayanagi, K., Schmitz, N., Selig, H., Sohl, F., Spilker, T., Srama, R., Stephan, K., Touboul, P., Wolf, P., 2012, ExA, 34, 203, OSS (Outer Solar System): a fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt
    The present OSS (Outer Solar System) mission continues a long and bright tradition by associating the communities of fundamental physics and planetary sciences in a single mission with ambitious goals in both domains. OSS is an M-class mission to explore the Neptune system almost half a century after the flyby of the Voyager 2 spacecraft. Several discoveries were made by Voyager 2, including the Great Dark Spot (which has now disappeared) and Triton's geysers. Voyager 2 revealed the dynamics of Neptune's atmosphere and found four rings and evidence of ring arcs above Neptune. Benefiting from a greatly improved instrumentation, a mission as OSS would result in a striking advance in the study of the farthest planet of the solar system. Furthermore, OSS would provide a unique opportunity to visit a selected Kuiper Belt object subsequent to the passage of the Neptunian system. OSS would help consolidate the hypothesis of the origin of Triton as a Kuiper Belt object captured by Neptune, and to improve our knowledge on the formation of the solar system. The OSS probe would carry instruments allowing precise tracking of the spacecraft during the cruise. It would facilitate the best possible tests of the laws of gravity in deep space. These objectives are important for fundamental physics, as they test General Relativity, our current theoretical description of gravitation, but also for cosmology, astrophysics and planetary science, as General Relativity is used as a tool in all these domains. In particular, the models of solar system formation uses General Relativity to describe the crucial role of gravity. OSS is proposed as an international cooperation between ESA and NASA, giving the capability for ESA to launch an M-class mission towards the farthest planet of the solar system, and to a Kuiper Belt object. The proposed mission profile would allow to deliver a 500 kg class spacecraft. The design of the probe is mainly constrained by the deep space gravity test in order to minimize the perturbation of the accelerometer measurement.
  13. Shkolnik, E., Anglada-Escude, G., Liu, M., Bowler, B., Weinberger, A., Boss, A., Reid, I., Tamura, M., 2012, ApJ, 758, 56, Identifying the Young Low-mass Stars within 25 pc. II. Distances, Kinematics, and Group Membership
    We have conducted a kinematic study of 165 young M dwarfs with ages of lsim300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of lsim25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (lsim3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages lsim150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event.

    Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope, the du Pont Telescope at Las Campanas Observatory, and the Subaru Telescope. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. The CFHT is operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

  14. Burgasser, A., Luk, C., Dhital, S., Bardalez Gagliuffi, D., Nicholls, C., Prato, L., West, A., Lepine, S., 2012, ApJ, 757, 110, Discovery of a Very Low Mass Triple with Late-M and T Dwarf Components: LP 704-48/SDSS J0006-0852AB
    We report the identification of the M9 dwarf SDSS J000649.16-085246.3 as a spectral binary and radial velocity (RV) variable with components straddling the hydrogen-burning mass limit. Low-resolution near-infrared spectroscopy reveals spectral features indicative of a T dwarf companion, and spectral template fitting yields component types of M8.5 0.5 and T5 1. High-resolution near-infrared spectroscopy with Keck/NIRSPEC reveals pronounced RV variations with a semi-amplitude of 8.2 0.4 km s-1. From these we determine an orbital period of 147.6 1.5 days and eccentricity of 0.10 0.07, making SDSS J0006-0852AB the third tightest very low mass binary known. This system is also found to have a common proper motion companion, the inactive M7 dwarf LP 704-48, at a projected separation of 820 120 AU. The lack of H emission in both M dwarf components indicates that this system is relatively old, as confirmed by evolutionary model analysis of the tight binary. LP 704-48/SDSS J0006-0852AB is the lowest-mass confirmed triple identified to date, and one of only seven candidate and confirmed triples with total masses below 0.3 M currently known. We show that current star and brown dwarf formation models cannot produce triple systems like LP 704-48/SDSS J0006-0852AB, and we rule out Kozai-Lidov perturbations and tidal circularization as a viable mechanism to shrink the inner orbit. The similarities between this system and the recently uncovered low-mass eclipsing triples NLTT 41135AB/41136 and LHS 6343ABC suggest that substellar tertiaries may be common in wide M dwarf pairs.

    Portions of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  15. Dunham, E., Bida, T., Collins, P., Mandushev, G., McLean, I., Person, M., Smith, E., Taylor, B., Zoonematkermani, S., 2012, SPIE, 8446, 844618, HIPO in-flight performance aboard SOFIA
    HIPO is a special purpose science instrument for SOFIA that was also designed to be used for Observatory test work. It was used in a series of flights from June to December 2011 as part of the SOFIA Characterization and Integration (SCAI) flight test program. Partial commissioning of HIPO and the co-mounted HIPO-FLITECAM (FLIPO) configuration were included within the scope of the SCAI work. The commissioning measurements included such things as optical throughput, image size and shape as a function of wavelength and exposure time, image motion assessment over a wide frequency range, scintillation noise, photometric stability assessment, twilight sky brightness, cosmic ray rate as a function of altitude, telescope pointing control, secondary mirror control, and GPS time and position performance. As part of this work we successfully observed a stellar occultation by Pluto, our first SOFIA science data. We report here on the observed in-flight performance of HIPO both when mounted alone and when used in the FLIPO configuration.
  16. McLean, I., Smith, E., Becklin, E., Dunham, E., Milburn, J., Savage, M., 2012, SPIE, 8446, 844619, FLITECAM: current status and results from observatory verification flights
    This paper describes the current status of FLITECAM, the near-infrared (1 - 5 m) camera and spectrometer for NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA). Due to a change in schedule FLITECAM's delivery was advanced, allowing it to be co-mounted with the HIPO instrument and used on four flights in October 2011 for observatory verification. Although not part of FLITECAM's commissioning time, some preliminary performance characteristics were determined. Image size as a function of wavelength was measured prior to the installation of active mass dampers on the telescope. Preliminary grism spectroscopy was also obtained. In addition, FLITECAM was used to measure the emissivity of the telescope and warm optics in the co-mounted configuration. New narrow band filters were added to the instrument, including a Paschen alpha filter for line emission. Results are illustrated.
  17. McElwain, M., Mandell, A., Woodgate, B., Spiegel, D., Madhusudhan, N., Amatucci, E., Blake, C., Budinoff, J., Burgasser, A., Burrows, A., Clampin, M., Conroy, C., Deming, L., Dunham, E., Foltz, R., Gong, Q., Knutson, H., Muench, T., Murray-Clay, R., Peabody, H., Rauscher, B., Rinehart, S., Villanueva, G., 2012, SPIE, 8446, 84467B, NIMBUS: the Near-infrared Multi-Band Ultraprecise Spectroimager for SOFIA
    We present a new and innovative near-infrared multi-band ultraprecise spectroimager (NIMBUS) for SOFIA. This design is capable of characterizing a large sample of extrasolar planet atmospheres by measuring elemental and molecular abundances during primary transit and occultation. This wide-field spectroimager would also provide new insights into Trans-Neptunian Objects (TNO), Solar System occultations, brown dwarf atmospheres, carbon chemistry in globular clusters, chemical gradients in nearby galaxies, and galaxy photometric redshifts. NIMBUS would be the premier ultraprecise spectroimager by taking advantage of the SOFIA observatory and state of the art infrared technologies. This optical design splits the beam into eight separate spectral bandpasses, centered around key molecular bands from 1 to 4m. Each spectral channel has a wide field of view for simultaneous observations of a reference star that can decorrelate time-variable atmospheric and optical assembly effects, allowing the instrument to achieve ultraprecise calibration for imaging and photometry for a wide variety of astrophysical sources. NIMBUS produces the same data products as a low-resolution integral field spectrograph over a large spectral bandpass, but this design obviates many of the problems that preclude high-precision measurements with traditional slit and integral field spectrographs. This instrument concept is currently not funded for development.
  18. Foote, E., Paige, D., Shepard, M., Johnson, J., Grundy, W., Biggar, S., Greenhagen, B., Allen, C., 2012, epsc, EPSC2012-297, Solar Reflectance Measurements of Apollo Lunar Soils
    The moon is the one planetary object from which we have returned samples. The goal of this work is to analyze and understand the solar reflectance of the Moon. Our approach is to compare Lunar Reconnaissance Orbiter (LRO) Diviner orbital solar albedo measurements at the Apollo soil sample sites with laboratory bidirectional reflectance measurements. CAPTEM provided us with five representative lunar soil samples: a typical low albedo mare sample (10084, Apollo 11), a low titanium basaltic sample with impact breccias (12001, Apollo 12), an Apollo 15 sample (15071), a high albedo lunar highlands soil (68810 & 61141, Apollo 16) and an Apollo 17 soil sample (70181). The laboratory and Diviner datasets provide complementary and independent insights into the photometric properties of the lunar surface. We have made the most extensive set of laboratory bidirectional measurements of lunar soil to date and have successfully fit photometric models to the laboratory data.
  19. Lamy, P., Faury, G., Llebaria, A., Knight, M., A'Hearn, M., 2012, epsc, EPSC2012-308, Sunskirting comets discovered with the LASCO coronagraphs (1996-2008)
    In addition to an unprecedented number of Kreutz sungrazing comets, the LASCO coronagraphs aboard SOHO have discovered some 238 unrelated "sunskirting" comets from 1996 to 2008. This new family is organized in several groups, and two comets have further been found periodic. We present the photometry and the heliocentric light curves of these sunskirting comets. The bulk of them exhibit a continuous increase of the brightness as the comet approaches, reaching a peak before perihelion and then progressively fading with a large variety of brightness gradients. However, some of them have peak brightness either at or post-perihelion whereas a quite large number are approximately flat. We finally characterize the different groups of sunskirters on the basis of their distribution of peak magnitudes and of their fragmentation history.
  20. Young, E., Herter, T., Gusten, R., Dunham, E., Becklin, E., Marcum, P., Krabbe, A., Andersson, B., Reach, W., Zinnecker, H., 2012, SPIE, 8444, 844410, Early science results from SOFIA
    SOFIA, the Stratospheric Observatory for Infrared Astronomy, is an airborne observatory with a 2.7-m telescope that is under development by NASA and the German Aerospace Center DLR. From late 2010 and through the end of 2011, SOFIA conducted a series of science demonstration flights, Early Science, using FORCAST (the Faint Object InfraRed Camera for the SOFIA Telescope), HIPO (the High-speed Imaging Photometer for Occultations), and GREAT (the German REceiver for Astronomy at Terahertz frequencies). Flying at altitudes as high as 13.7 km (45,000 ft), SOFIA operates above more than 99.8% of the water vapor in the Earths atmosphere, opening up most of the far-infrared and sub-millimeter parts of the spectrum. During Early Science, 30 science missions were flown with results in solar system astronomy, star formation, the interstellar medium, the Galactic Center, and extragalactic studies. Many of these investigations were conducted by the first group of SOFIA General Investigators, demonstrating the operation of SOFIA as a facility for the astronomical community. This paper presents some recent highlights from Early Science.
  21. Keas, P., Dunham, E., Lampater, U., Pfuller, E., Teufel, S., Roeser, H., Wiedemann, M., Wolf, J., 2012, SPIE, 8444, 844411, Active damping of the SOFIA Telescope assembly
    The NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA) employs a 2.5-meter reflector telescope in a Boeing 747SP. The telescope is housed in an open cavity and is subjected to aeroacoustic and inertial disturbances in flight. To meet pointing requirements, SOFIA must achieve a pointing stability of approximately 0.5 arcseconds RMS. An active damping control system is being developed for SOFIA to reduce image jitter and image degradation due to resonance of the telescope assembly. Our paper discusses the history of the active damping design for SOFIA, from early concepts to the current implementation which has recently completed a ground and flight testing for proof-of-concept. We describe some milestones in the analysis and testing of the telescope assembly which guided the development of the vibration control system. The control synthesis approach and current implementation of the active damping control system is presented. Finally, we summarize the performance observed in early flight tests and the steps that are currently foreseen to completing the development of this system.
  22. Temi, P., Marcum, P., Miller, W., Dunham, E., McLean, I., Wolf, J., Becklin, E., Bida, T., Brewster, R., Casey, S., Collins, P., Horner, S., Jakob, H., Jensen, S., Killebrew, J., Lampater, U., Mandushev, G., Meyer, A., Pfueller, E., Reinacher, A., Rho, J., Roellig, T., Savage, M., Smith, E., Teufel, S., Wiedemann, M., 2012, SPIE, 8444, 844414, SOFIA observatory performance and characterization
    The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently concluded a set of engineering flights for Observatory performance evaluation. These in-flight opportunities have been viewed as a first comprehensive assessment of the Observatory's performance and will be used to address the development activity that is planned for 2012, as well as to identify additional Observatory upgrades. A series of 8 SOFIA Characterization And Integration flights have been conducted from June to December 2011. The HIPO science instrument in conjunction with the DSI Super Fast Diagnostic Camera (SFDC) have been used to evaluate pointing stability, including the image motion due to rigid-body and flexible-body telescope modes as well as possible aero-optical image motion. We report on recent improvements in pointing stability by using an Active Mass Damper system installed on Telescope Assembly. Measurements and characterization of the shear layer and cavity seeing, as well as image quality evaluation as a function of wavelength have been performed using the HIPO+FLITECAM Science Instrument conguration (FLIPO). A number of additional tests and measurements have targeted basic Observatory capabilities and requirements including, but not limited to, pointing accuracy, chopper evaluation and imager sensitivity. This paper reports on the data collected during these flights and presents current SOFIA Observatory performance and characterization.
  23. Levine, S., Bida, T., Chylek, T., Collins, P., DeGroff, W., Dunham, E., Lotz, P., Venetiou, A., Zoonemat Kermani, S., 2012, SPIE, 8444, 844419, Status and performance of the Discovery Channel Telescope during commissioning
    Lowell Observatory's Discovery Channel Telescope is a 4.3m telescope designed for optical and near infrared astronomical observation. At first light, the telescope will have a cube capable of carrying five instruments and the wave front sensing and guider system at the f/6.1 RC focus. The corrected RC focus field of view is 30 in diameter. Nasmyth and prime focus can be instrumented subsequently. Early commissioning work with the installed primary mirror and its support system started out using one of the wave front sensing probes mounted at prime focus, and has continued at RC with the recent installation of the secondary mirror. We will report on the on-sky pointing and tracking performance of the telescope, initial assessment of the functionality of the active optics support system, and tests of the early image quality of the telescope and optics. We will also describe the suite of first light instruments, and early science operations.
  24. Venetiou, A., Bida, T., 2012, SPIE, 8444, 84441E, Discovery Channel Telescope active optics system early integration and test
    The Discovery Channel Telescope (DCT) is a 4.3-meter telescope with a thin meniscus primary mirror (M1) and a honeycomb secondary mirror (M2). The optical design is an f/6.1 Ritchey-Chretien (RC) with an unvignetted 0.5 Field of View (FoV) at the Cassegrain focus. We describe the design, implementation and performance of the DCT active optics system (AOS). The DCT AOS maintains collimation and controls the figure of the mirror to provide seeing-limited images across the focal plane. To minimize observing overhead, rapid settling times are achieved using a combination of feed-forward and low-bandwidth feedback control using a wavefront sensing system. In 2011, we mounted a Shack-Hartmann wavefront sensor at the prime focus of M1, the Prime Focus Test Assembly (PFTA), to test the AOS with the wavefront sensor, and the feedback loop. The incoming wavefront is decomposed using Zernike polynomials, and the mirror figure is corrected with a set of bending modes. Components of the system that we tested and tuned included the Zernike to Bending Mode transformations. We also started open-loop feed-forward coefficients determination. In early 2012, the PFTA was replaced by M2, and the wavefront sensor moved to its normal location on the Cassegrain instrument assembly. We present early open loop wavefront test results with the full optical system and instrument cube, along with refinements to the overall control loop operating at RC Cassegrain focus.
  25. Bida, T., Dunham, E., Nye, R., Chylek, T., Oliver, R., 2012, SPIE, 8444, 844451, Design, development, and testing of the DCT Cassegrain instrument support assembly
    The 4.3m Discovery Channel Telescope delivers an f/6.1 unvignetted 0.5 field to its RC focal plane. In order to support guiding, wavefront sensing, and instrument installations, a Cassegrain instrument support assembly has been developed which includes a facility guider and wavefront sensor package (GWAVES) and multiple interfaces for instrumentation. A 2-element, all-spherical, fused-silica corrector compensates for field curvature and astigmatism over the 0.5 FOV, while reducing ghost pupil reflections to minimal levels. Dual roving GWAVES camera probes pick off stars in the outer annulus of the corrected field, providing simultaneous guiding and wavefront sensing for telescope operations. The instrument cube supports 5 co-mounted instruments with rapid feed selection via deployable fold mirrors. The corrected beam passes through a dual filter wheel before imaging with the 6K x 6K single CCD of the Large Monolithic Imager (LMI). We describe key development strategies for the DCT Cassegrain instrument assembly and GWAVES, including construction of a prime focus test assembly with wavefront sensor utilized in fall 2011 to begin characterization of the DCT primary mirror support. We also report on 2012 on-sky test results of wavefront sensing, guiding, and imaging with the integrated Cassegrain cube.
  26. Finley, D., Smith, B., DeGroff, B., 2012, SPIE, 8449, 84490S, Incentive contracts for development projects
    Finding a contract vehicle that balances the concerns of the customer and the contractor in a development project can be difficult. The customer wants a low price and an early delivery, with as few surprises as possible as the project progresses. The contractor wants sufficient cost and schedule to cover risk. Both want to clearly define what each party will provide. Many program offices do not want to award cost plus contracts because their funding sources will not allow it, their boards do not want an open ended commitment, and they feel like they lose financial control of the project. A fixed price incentive contract, with a mutually agreed upon target cost, provides the owner with visibility into the project and input into the execution of the project, encourages both parties to save costs, and stimulates a collaborative atmosphere by aligning the respective interests of customers and contractors.
  27. Lotz, P., Lacasse, M., Godwin, R., 2012, SPIE, 8451, 845108, Discovery Channel Telescope software component template and state design: principles and implementation
    The Discovery Channel Telescope is a 4.3m astronomical research telescope in northern Arizona constructed through a partnership between Discovery Communications and Lowell Observatory. The control software for the telescope and observatory systems consists of stand-alone, state-based components that respond to triggers (external signals or internal data changes). Component applications execute on Windows, real-time, and FPGA targets. The team has developed a template for a system component, the implementation of which has yielded large gains in productivity, robustness, and maintainability. These benefits follow from the dependence of the template on common, well-tested code, allowing a developer to focus on application-specific particulars unencumbered by details of infrastructure elements such as communication, and from the separation of concerns the architecture provides, ensuring that modifications are straightforward, separable, and consequently relatively safe. We describe a repeatable design process for developing a state machine design, and show how this translates directly into a concrete implementation utilizing several design patterns, illustrating this with examples from components of the functioning active optics system. We also present a refined top-level state machine design and rules for highly independent component interactions within and between hierarchies that we propose offer a general solution for large component-based control systems.
  28. Raiteri, C., Villata, M., Smith, P., Larionov, V., Acosta-Pulido, J., Aller, M., D'Ammando, F., Gurwell, M., Jorstad, S., Joshi, M., Kurtanidze, O., Lahteenmaki, A., Mirzaqulov, D., Agudo, I., Aller, H., Arevalo, M., Arkharov, A., Bach, U., Benitez, E., Berdyugin, A., Blinov, D., Blumenthal, K., Buemi, C., Bueno, A., Carleton, T., Carnerero, M., Carosati, D., Casadio, C., Chen, W., Di Paola, A., Dolci, M., Efimova, N., Ehgamberdiev, S., Gomez, J., Gonzalez, A., Hagen-Thorn, V., Heidt, J., Hiriart, D., Holikov, S., Konstantinova, T., Kopatskaya, E., Koptelova, E., Kurtanidze, S., Larionova, E., Larionova, L., Leon-Tavares, J., Leto, P., Lin, H., Lindfors, E., Marscher, A., McHardy, I., Molina, S., Morozova, D., Mujica, R., Nikolashvili, M., Nilsson, K., Ovcharov, E., Panwar, N., Pasanen, M., Puerto-Gimenez, I., Reinthal, R., Richter, G., Ros, J., Sakamoto, T., Schwartz, R., Sillanpaa, A., Smith, N., Takalo, L., Tammi, J., Taylor, B., Thum, C., Tornikoski, M., Trigilio, C., Troitsky, I., Umana, G., Valcheva, A., Wehrle, A., 2012, A&A, 545, A48, Variability of the blazar 4C 38.41 (B3 1633+382) from GHz frequencies to GeV energies
    Context. After years of modest optical activity, the quasar-type blazar 4C 38.41 (B3 1633+382) experienced a large outburst in 2011, which was detected throughout the entire electromagnetic spectrum, renewing interest in this source.
    Aims: We present the results of low-energy multifrequency monitoring by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) consortium and collaborators, as well as those of spectropolarimetric/spectrophotometric monitoring at the Steward Observatory. We also analyse high-energy observations of the Swift and Fermi satellites. This combined study aims to provide insights into the source broad-band emission and variability properties.
    Methods: We assemble optical, near-infrared, millimetre, and radio light curves and investigate their features and correlations. In the optical, we also analyse the spectroscopic and polarimetric properties of the source. We then compare the low-energy emission behaviour with that at high energies.
    Results: In the optical-UV band, several results indicate that there is a contribution from a quasi-stellar-object (QSO) like emission component, in addition to both variable and polarised jet emission. In the optical, the source is redder-when-brighter, at least for R 16. The optical spectra display broad emission lines, whose flux is constant in time. The observed degree of polarisation increases with flux and is higher in the red than the blue. The spectral energy distribution reveals a bump peaking around the U band. The unpolarised emission component is likely thermal radiation from the accretion disc that dilutes the jet polarisation. We estimate its brightness to be RQSO ~ 17.85-18 and derive the intrinsic jet polarisation degree. We find no clear correlation between the optical and radio light curves, while the correlation between the optical and -ray flux apparently fades in time, likely because of an increasing optical to -ray flux ratio.
    Conclusions: As suggested for other blazars, the long-term variability of 4C 38.41 can be interpreted in terms of an inhomogeneous bent jet, where different emitting regions can change their alignment with respect to the line of sight, leading to variations in the Doppler factor . Under the hypothesis that in the period 2008-2011 all the -ray and optical variability on a one-week timescale were due to changes in , this would range between ~7 and ~21. If the variability were caused by changes in the viewing angle only, then would go from ~2.6 to ~5. Variations in the viewing angle would also account for the dependence of the polarisation degree on the source brightness in the framework of a shock-in-jet model.

    The radio-to-optical data collected by the GASP-WEBT collaboration are stored in the GASP-WEBT archive; for questions regarding their availability, please contact the WEBT President Massimo Villata.

  29. Xiao, H., Covey, K., Rebull, L., Charbonneau, D., Mandushev, G., O'Donovan, F., Slesnick, C., Lloyd, J., 2012, ApJS, 202, 7, A Census of Rotation and Variability in L1495: A Uniform Analysis of Trans-atlantic Exoplanet Survey Light Curves for Pre-main-sequence Stars in Taurus
    We analyze light curves obtained by the Trans-atlantic Exoplanet Survey (TrES) for a field centered on the L1495 dark cloud in Taurus. The Spitzer Taurus Legacy Survey catalog identifies 179 bona fide Taurus members within the TrES field; 48 of the known Taurus members are detected by TrES, as well as 26 candidate members identified by the Spitzer Legacy team. We quantify the variability of each star in our sample using the ratio of the standard deviation of the original light curve (orig.) to the standard deviation of a light curve that has been smoothed by 9 or 1001 epochs (9 and 1001, respectively). Known Taurus members typically demonstrate (orig./9) < 2.0, and (orig./1001) < 5, while field stars reveal (orig./9) ~ 3.0 and (orig./1001) ~ 10, as expected for light curves dominated by unstructured white noise. Of the 74 Taurus members/candidates with TrES light curves, we detect significant variability in 49 sources. Adapting a quantitative metric originally developed to assess the reliability of transit detections, we measure the amount of red and white noise in each light curve and identify 18 known or candidate Taurus members with highly significant period measurements. These appear to be the first periods measured for four of these sources (HD 282276, CX Tau, FP Tau, TrES J042423+265008), and in two other cases, the first non-aliased periods (LkCa 21 and DK Tau AB). For the remainder, the TrES measurements typically agree very well (P < 1%) with previously reported values. Including periods measured at lower confidence for 15 additional sources, we report periods for 11 objects where no previous periods were found, including 8 confirmed Taurus members. We also identify 10 of the 26 candidate Taurus members that demonstrate variability levels consistent with being bona fide T Tauri stars. A Kolomgorov-Smirnov (K-S) test confirms that these new periods confirm the distinction between the rotation period distributions of stars with and without circumstellar disks, with only a 10% probability of the two populations sharing the same parent period distribution. K-S tests do suggest, however, that the updated Taurus period distribution now more closely resembles those measured in other young star-forming clusters (i.e., NGC 2264, NGC 6530, and the ONC). This improved agreement may reflect the exclusion of long rotation periods which are detected in Taurus at lower significance, and which may be beyond the limits of detectability in more distant star-forming regions.
  30. Bowler, B., Liu, M., Shkolnik, E., Tamura, M., 2012, ApJ, 756, 69, Planets around Low-mass Stars (PALMS). II. A Low-mass Companion to the Young M Dwarf GJ 3629 Separated by 0.2"
    We present the discovery of a 0.2" companion to the young M dwarf GJ 3629 as part of our high-contrast adaptive optics imaging search for giant planets around low-mass stars with the Keck-II and Subaru telescopes. Two epochs of imaging confirm that the pair is comoving and reveal signs of orbital motion. The primary exhibits saturated X-ray emission which, together with its UV photometry from GALEX, points to an age younger than ~300 Myr. At these ages the companion lies below the hydrogen burning limit with a model-dependent mass of 46 16 M Jup based on the system's photometric distance of 22 3 pc. Resolved YJHK photometry of the pair indicates a spectral type of M7 2 for GJ 3629 B. With a projected separation of 4.4 0.6 AU and an estimated orbital period of 21 5 yr, GJ 3629 AB is likely to yield a dynamical mass in the next several years, making it one of only a handful of brown dwarfs to have a measured mass and an age constrained from the stellar primary.

    Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  31. Schaefer, G., Prato, L., Simon, M., Zavala, R., 2012, ApJ, 756, 120, Orbit and Stellar Properties of the Young Triple V807 Tau
    We present new orbital measurements of the pre-main-sequence triple system, V807 Tau, using adaptive optics imaging at the Keck Observatory. We computed an orbit for the close pair, V807 Tau Ba-Bb, with a period of 12.312 0.058 years and a semi-major axis of 38.59 0.16 mas. By modeling the center of mass motion of the components in the close pair relative to the wide component, V807 Tau A, we measured a mass ratio of 0.843 0.050 for Bb/Ba. Combined with the total mass from the relative orbit, we derived individual masses of M Ba = 0.564 0.018 (d/140 pc)3 M and M Bb = 0.476 0.017 (d/140 pc)3 M at an average distance of 140 pc to the Taurus star-forming region. We computed spectral energy distributions to determine the luminosities of the three components. We also measured their spectral types, effective temperatures, and rotational velocities based on spatially resolved spectra obtained at the Keck Observatory. If the rotational axes are aligned, then the projected rotational velocities imply that V807 Tau Ba and Bb are rotating much faster than V807 Tau A. The uncertainty in the stellar effective temperatures and distance to the system currently limit the comparison of our dynamical mass measurements with predictions based on evolutionary tracks for pre-main-sequence stars. We also report preliminary results from a program to map the 3.6 cm radio emission from V807 Tau using the Very Long Baseline Array. With continued monitoring, these observations will provide a precise parallax for placing the dynamical masses on an absolute scale.
  32. Zhang, H., Hunter, D., Elmegreen, B., Gao, Y., Schruba, A., 2012, IAUS, 284, 345, Radial variations of the SFHs of dwarf irregular galaxies
    The LITTLE THINGS project has compiled multi-wavelength data (including VLA hi-line emission maps, GALEX FUV/NUV imagery, UBV, narrow-band H, and Spitzer images) for a representative sample of nearby dwarf irregular (dIrr) galaxies. The broadband data are used to constrain the radial variations of the star formation (SF) rate (SFR) averaged over the past 0.1 Gyr, 1 Gyr and a Hubble time, with a complete library of model SF histories (SFHs). The recent SF of more than ~ 80% of the dIrrs in our sample has been concentrated in the inner disk, and the SF in the outer disk has been markedly suppressed. This outside-in shrinking of the star-forming disk leaves a down-bending (double exponential) stellar mass surface density (*) distribution. Our findings in dIrrs are in contrast to the inside-out disk growth scenario suggested for luminous spiral galaxies.
  33. Porter, S., Grundy, W., 2012, Icar, 220, 947, KCTF evolution of trans-neptunian binaries: Connecting formation to observation
    Recent observational surveys of trans-neptunian binary (TNB) systems have dramatically increased the number of known mutual orbits. Our Kozai Cycle Tidal Friction (KCTF) simulations of synthetic trans-neptunian binaries show that tidal dissipation in these systems can completely reshape their original orbits. Specifically, solar torques should have dramatically accelerated the semimajor axis decay and circularization timescales of primordial (or recently excited) TNBs. As a result, our initially random distribution of TNBs in our simulations evolved to have a large population of tight circular orbits. This tight circular population appears for a range of TNO physical properties, though a strong gravitational quadrupole can prevent some from fully circularizing. We introduce a stability parameter to predict the effectiveness of KCTF on a TNB orbit, and show that a number of known TNBs must have a large gravitational quadrupole to be stable.
  34. Howard, A., Marcy, G., Bryson, S., Jenkins, J., Rowe, J., Batalha, N., Borucki, W., Koch, D., Dunham, E., Gautier, T., Van Cleve, J., Cochran, W., Latham, D., Lissauer, J., Torres, G., Brown, T., Gilliland, R., Buchhave, L., Caldwell, D., Christensen-Dalsgaard, J., Ciardi, D., Fressin, F., Haas, M., Howell, S., Kjeldsen, H., Seager, S., Rogers, L., Sasselov, D., Steffen, J., Basri, G., Charbonneau, D., Christiansen, J., Clarke, B., Dupree, A., Fabrycky, D., Fischer, D., Ford, E., Fortney, J., Tarter, J., Girouard, F., Holman, M., Johnson, J., Klaus, T., Machalek, P., Moorhead, A., Morehead, R., Ragozzine, D., Tenenbaum, P., Twicken, J., Quinn, S., Isaacson, H., Shporer, A., Lucas, P., Walkowicz, L., Welsh, W., Boss, A., Devore, E., Gould, A., Smith, J., Morris, R., Prsa, A., Morton, T., Still, M., Thompson, S., Mullally, F., Endl, M., MacQueen, P., 2012, ApJS, 201, 15, Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
    We report the distribution of planets as a function of planet radius, orbital period, and stellar effective temperature for orbital periods less than 50 days around solar-type (GK) stars. These results are based on the 1235 planets (formally "planet candidates") from the Kepler mission that include a nearly complete set of detected planets as small as 2 R . For each of the 156,000 target stars, we assess the detectability of planets as a function of planet radius, R p, and orbital period, P, using a measure of the detection efficiency for each star. We also correct for the geometric probability of transit, R sstarf/a. We consider first Kepler target stars within the "solar subset" having T eff = 4100-6100 K, log g = 4.0-4.9, and Kepler magnitude Kp < 15 mag, i.e., bright, main-sequence GK stars. We include only those stars having photometric noise low enough to permit detection of planets down to 2 R . We count planets in small domains of R p and P and divide by the included target stars to calculate planet occurrence in each domain. The resulting occurrence of planets varies by more than three orders of magnitude in the radius-orbital period plane and increases substantially down to the smallest radius (2 R ) and out to the longest orbital period (50 days, ~0.25 AU) in our study. For P < 50 days, the distribution of planet radii is given by a power law, df/dlog R = kRR with kR = 2.9+0.5 - 0.4, = -1.92 0.11, and R R p/R . This rapid increase in planet occurrence with decreasing planet size agrees with the prediction of core-accretion formation but disagrees with population synthesis models that predict a desert at super-Earth and Neptune sizes for close-in orbits. Planets with orbital periods shorter than 2 days are extremely rare; for R p > 2 R we measure an occurrence of less than 0.001 planets per star. For all planets with orbital periods less than 50 days, we measure occurrence of 0.130 0.008, 0.023 0.003, and 0.013 0.002 planets per star for planets with radii 2-4, 4-8, and 8-32 R , in agreement with Doppler surveys. We fit occurrence as a function of P to a power-law model with an exponential cutoff below a critical period P 0. For smaller planets, P 0 has larger values, suggesting that the "parking distance" for migrating planets moves outward with decreasing planet size. We also measured planet occurrence over a broader stellar T eff range of 3600-7100 K, spanning M0 to F2 dwarfs. Over this range, the occurrence of 2-4 R planets in the Kepler field increases with decreasing T eff, with these small planets being seven times more abundant around cool stars (3600-4100 K) than the hottest stars in our sample (6600-7100 K).

    Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology.

  35. Judge, P., Lockwood, G., Radick, R., Henry, G., Shapiro, A., Schmutz, W., Lindsey, C., 2012, A&A, 544, A88, Confronting a solar irradiance reconstruction with solar and stellar data
    Context. A recent paper by Shapiro and colleagues (2011, A&A, 529, A67) reconstructs spectral and total irradiance variations of the Sun during the holocene. Aims. In this note, we comment on why their methodology leads to large (0.5%) variations in the solar TSI on century-long time scales, in stark contrast to other reconstructions which have 0.1% variations. Methods. We examine the amplitude of the irradiance variations from the point of view of both solar and stellar data. Results. Shapiro et al.'s large amplitudes arise from differences between the irradiances computed from models A and C of Fontenla and colleagues, and from their explicit assumption that the radiances of the quiet Sun vary with the cosmic ray modulation potential. We suggest that the upper photosphere, as given by model A, is too cool, and discuss relative contributions of local vs. global dynamos to the magnetism and irradiance of the quiet Sun. We compare the slow (>22 yr) components of the irradiance reconstructions with secular changes in stellar photometric data that span 20 years or less, and find that the Sun, if varying with such large amplitudes, would still lie within the distribution of stellar photometric variations measured over a 10-20 year period. However, the stellar time series are individually too short to see if the reconstructed variations will remain consistent with stellar variations when observed for several decades more. Conclusions. By adopting model A, Shapiro et al. have over-estimated quiet-Sun irradiance variations by about a factor of two, based upon a re-analysis of sub-mm data from the James Clerk Maxwell telescope. But both estimates are within bounds set by current stellar data. It is therefore vital to continue accurate photometry of solar-like stars for at least another decade, to reveal secular and cyclic variations on multi-decadal time scales of direct interest to the Sun.
  36. Vigan, A., Patience, J., Marois, C., Bonavita, M., De Rosa, R., Macintosh, B., Song, I., Doyon, R., Zuckerman, B., Lafreniere, D., Barman, T., 2012, A&A, 544, A9, The International Deep Planet Survey. I. The frequency of wide-orbit massive planets around A-stars
    Breakthrough direct detections of planetary companions orbiting A-type stars confirm the existence of massive planets at relatively large separations, but dedicated surveys are required to estimate the frequency of similar planetary systems. To measure the first estimation of the giant exoplanetary systems frequency at large orbital separation around A-stars, we have conducted a deep-imaging survey of young (8-400 Myr), nearby (19-84 pc) A- and F-stars to search for substellar companions in the ~10-300 AU range. The sample of 42 stars combines all A-stars observed in previous AO planet search surveys reported in the literature with new AO observations from VLT/NaCo and Gemini/NIRI. It represents an initial subset of the International Deep Planet Survey (IDPS) sample of stars covering M- to B-stars. The data were obtained with diffraction-limited observations in H- and Ks-band combined with angular differential imaging to suppress the speckle noise of the central stars, resulting in typical 5 detection limits in magnitude difference of 12 mag at 1'', 14 mag at 2'' and 16 mag at 5'' which is sufficient to detect massive planets. A detailed statistical analysis of the survey results is performed using Monte Carlo simulations. Considering the planet detections, we estimate the fraction of A-stars having at least one massive planet (3-14 MJup) in the range 5-320 AU to be inside 5.9-18.8% at 68% confidence, assuming a flat distribution for the mass of the planets. By comparison, the brown dwarf (15-75 MJup) frequency for the sample is 2.0-8.9% at 68% confidence in the range 5-320 AU. Assuming power law distributions for the mass and semimajor axis of the planet population, the AO data are consistent with a declining number of massive planets with increasing orbital radius which is distinct from the rising slope inferred from radial velocity (RV) surveys around evolved A-stars and suggests that the peak of the massive planet population around A-stars may occur atseparations between the ranges probed by existing RV and AO observations. Finally, we report the discovery of three new close M-star companions to HIP 104365 and HIP 42334.

    Based on observations collected at the European Southern Observatory, Chile, ESO programs 081.C-0519, 083.C-0706, 084.C-0605, 087.C-0559, 088.C-0477, and at the Gemini North observatory, Gemini programs GN-2007B-Q-59, GN-2008A-Q-77, GN-2008B-Q-64, GN-2009A-Q-80, GN-2009B-Q-93.Table A.1 is available in electronic form at http://www.aanda.orgTables 1, 3, and A.1 are also available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A9

  37. Hayashida, M., Madejski, G., Nalewajko, K., Sikora, M., Wehrle, A., Ogle, P., Collmar, W., Larsson, S., Fukazawa, Y., Itoh, R., Chiang, J., Stawarz, .., Blandford, R., Richards, J., Max-Moerbeck, W., Readhead, A., Buehler, R., Cavazzuti, E., Ciprini, S., Gehrels, N., Reimer, A., Szostek, A., Tanaka, T., Tosti, G., Uchiyama, Y., Kawabata, K., Kino, M., Sakimoto, K., Sasada, M., Sato, S., Uemura, M., Yamanaka, M., Greiner, J., Kruehler, T., Rossi, A., Macquart, J., Bock, D., Villata, M., Raiteri, C., Agudo, I., Aller, H., Aller, M., Arkharov, A., Bach, U., Benitez, E., Berdyugin, A., Blinov, D., Blumenthal, K., Bottcher, M., Buemi, C., Carosati, D., Chen, W., Di Paola, A., Dolci, M., Efimova, N., Forne, E., Gomez, J., Gurwell, M., Heidt, J., Hiriart, D., Jordan, B., Jorstad, S., Joshi, M., Kimeridze, G., Konstantinova, T., Kopatskaya, E., Koptelova, E., Kurtanidze, O., Lahteenmaki, A., Lamerato, A., Larionov, V., Larionova, E., Larionova, L., Leto, P., Lindfors, E., Marscher, A., McHardy, I., Molina, S., Morozova, D., Nikolashvili, M., Nilsson, K., Reinthal, R., Roustazadeh, P., Sakamoto, T., Sigua, L., Sillanpaa, A., Takalo, L., Tammi, J., Taylor, B., Tornikoski, M., Trigilio, C., Troitsky, I., Umana, G., 2012, ApJ, 754, 114, The Structure and Emission Model of the Relativistic Jet in the Quasar 3C 279 Inferred from Radio to High-energy -Ray Observations in 2008-2010
    We present time-resolved broadband observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. While investigating the previously reported -ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears to be delayed with respect to the -ray emission by about 10 days. X-ray observations reveal a pair of "isolated" flares separated by ~90 days, with only weak -ray/optical counterparts. The spectral structure measured by Spitzer reveals a synchrotron component peaking in the mid-infrared band with a sharp break at the far-infrared band during the -ray flare, while the peak appears in the millimeter (mm)/submillimeter (sub-mm) band in the low state. Selected spectral energy distributions are fitted with leptonic models including Comptonization of external radiation produced in a dusty torus or the broad-line region. Adopting the interpretation of the polarization swing involving propagation of the emitting region along a curved trajectory, we can explain the evolution of the broadband spectra during the -ray flaring event by a shift of its location from ~1 pc to ~4 pc from the central black hole. On the other hand, if the -ray flare is generated instead at sub-pc distance from the central black hole, the far-infrared break can be explained by synchrotron self-absorption. We also model the low spectral state, dominated by the mm/sub-mm peaking synchrotron component, and suggest that the corresponding inverse-Compton component explains the steady X-ray emission.
  38. Mace, G., Prato, L., Torres, G., Wasserman, L., Mathieu, R., McLean, I., 2012, AJ, 144, 55, Dynamical Measurements of the Young Upper Scorpius Triple NTTS 155808-2219
    The young, low-mass, triple system NTTS 155808-2219 (ScoPMS 20) was previously identified as a ~17 day period single-lined spectroscopic binary (SB) with a tertiary component at 0.21 arcsec. Using high-resolution infrared spectra, acquired with NIRSPEC on Keck II, both with and without adaptive optics (AO), we measured radial velocities (RVs) of all three components. Reanalysis of the single-lined visible light observations, made from 1987 to 1993, also yielded RV detections of the three stars. Combining visible light and infrared data to compute the orbital solution produces orbital parameters consistent with the single-lined solution and a mass ratio of q = 0.78 0.01 for the SB. We discuss the consistency between our results and previously published data on this system, our RV analysis with both observed and synthetic templates, and the possibility that this system is eclipsing, providing a potential method for the determination of the stars' absolute masses. Over the ~20 year baseline of our observations, we have measured the acceleration of the SB's center of mass in its orbit with the tertiary. Long-term, AO imaging of the tertiary will eventually yield dynamical data useful for component mass estimates.
  39. Grundy, W., Benecchi, S., Rabinowitz, D., Porter, S., Wasserman, L., Skiff, B., Noll, K., Verbiscer, A., Buie, M., Tourtellotte, S., Stephens, D., Levison, H., 2012, Icar, 220, 74, Mutual events in the Cold Classical transneptunian binary system Sila and Nunam
    Hubble Space Telescope observations between 2001 and 2010 resolved the binary components of the Cold Classical transneptunian object (79360) Sila-Nunam (provisionally designated 1997 CS29). From these observations we have determined the circular, retrograde mutual orbit of Nunam relative to Sila with a period of 12.50995 0.00036 days and a semimajor axis of 2777 19 km. A multi-year season of mutual events, in which the two near-equal brightness bodies alternate in passing in front of one another as seen from Earth, is in progress right now, and on 2011 February 1 UT, one such event was observed from two different telescopes. The mutual event season offers a rich opportunity to learn much more about this barely-resolvable binary system, potentially including component sizes, colors, shapes, and albedo patterns. The low eccentricity of the orbit and a photometric lightcurve that appears to coincide with the orbital period are consistent with a system that is tidally locked and synchronized, like the Pluto-Charon system. The orbital period and semimajor axis imply a system mass of (10.84 0.22) 1018 kg, which can be combined with a size estimate based on Spitzer and Herschel thermal infrared observations to infer an average bulk density of 0.72-0.23+0.37 g cm, comparable to the very low bulk densities estimated for small transneptunian binaries of other dynamical classes.
  40. Bowler, B., Liu, M., Shkolnik, E., Dupuy, T., Cieza, L., Kraus, A., Tamura, M., 2012, ApJ, 753, 142, Planets around Low-mass Stars (PALMS). I. A Substellar Companion to the Young M Dwarf 1RXS J235133.3+312720
    We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2farcs4 (~120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0+2 -1. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of ~10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 10 pc) indicate it is likely a member of the ~50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the ~200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 6 M Jup for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages.

    Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  41. Zhang, H., Hunter, D., Elmegreen, B., 2012, ApJ, 754, 29, H I Power Spectra and the Turbulent Interstellar Medium of Dwarf Irregular Galaxies
    H I spatial power spectra were determined for a sample of 24 nearby dwarf irregular galaxies selected from the Local Irregulars That Trace Luminosity Extremes-The H I Nearby Galaxy Survey sample. The two-dimensional power spectral indices asymptotically become a constant for each galaxy when a significant part of the line profile is integrated. For narrow channel maps, the power spectra become shallower as the channel width decreases, and this shallowing trend continues to our single channel maps. This implies that even the highest velocity resolution of 1.8 km s-1 is not smaller than the thermal dispersion of the coolest, widespread H I component. The one-dimensional power spectra of azimuthal profiles at different radii suggest that the shallower power spectra for narrower channel width is mainly contributed by the inner disks, which indicates that the inner disks have proportionally more cooler H I than the outer disks. Galaxies with lower luminosity (MB > -14.5 mag) and star formation rate (SFR, log(SFR (M yr-1)) < -2.1) tend to have steeper power spectra, which implies that the H I line-of-sight depths can be comparable with the radial length scales in low-mass galaxies. A lack of a correlation between the inertial-range spectral indices and SFR surface density implies that either non-stellar power sources are playing a fundamental role in driving the interstellar medium turbulent structure or the nonlinear development of turbulent structures has little to do with the driving sources.

    Based on data from the LITTLE THINGS Survey (D. A. Hunter et al., in preparation).

  42. Schmid, C., Abuter, R., Merand, A., Sahlmann, J., Alonso, J., Andolfato, L., van Belle, G., Delplancke, F., Derie, F., Di Lieto, N., Frahm, R., Gitton, P., Gomes, N., Haguenauer, P., Justen, B., Leveque, S., Menardi, S., Morel, S., Muller, A., Phan Duc, T., Pozna, E., Ramirez, A., Schuhler, N., Segransan, D., 2012, SPIE, 8445, 84450F, Status of PRIMA for the VLTI: heading to astrometry
    The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Since January 2011 the integration and individual testing of the different subsystem has come to a necessary minimum. At the same time the astrometric commissioning phase has begun. In this contribution we give an update on the status of the facility and present some highlights and difficulties on our way from first dual-feed fringe detection to first astrometric measurements. We focus on technical and operational aspects. In particular, within the context of the latter we are going to present a modified mode of operation that scans across the fringes. We will show that this mode, originally only intended for calibration purposes, facilitates the detection of dual-fringes.
  43. Jorgensen, A., Schmitt, H., van Belle, G., Mozurkewich, D., Hutter, D., Armstrong, J., Baines, E., Restaino, S., Hall, T., 2012, SPIE, 8445, 844519, Coherent integration in optical interferometry
    Optical Interferometry has long been limited by low SNR making it nearly impossible to measure the small visibilities required to make resolved images. Although the SNR exists in the raw data, much SNR is lost in the conventional squared-visibility processing. In modern interferometers fringes are recorded simultaneously at many wavelengths and baselines. This makes phase-referencing possible, which is the key to coherent integration, which in turns can greatly improve the SNR of measurements, making small-amplitude resolving measurements possible. In this paper we will detail the theory of coherent integration. We will also explain why coherent integration should, in most cases, be carried out during post-processing in software rather than in real-time in hardware. We will then compare it to conventional processing approaches for some data from the Navy Optical Interferometer. We will demonstrate how coherent integration can improve the accuracy of observations.
  44. Schmitt, H., Mozurkewich, D., Armstrong, J., Jorgensen, A., Baines, E., Restaino, S., Hindsley, R., van Belle, G., 2012, SPIE, 8445, 84452P, Simulated imaging with an interferometer on a boom
    We simulate the observations of a red supergiant star and an asteroid with an optical interferometer mounted on a boom. This instrument has an advantage over more traditional interferometers because it significantly reduces the number of reflections and surfaces, thus allowing one to combine a larger number of telescopes without a significant loss of sensitivity. We investigate two telescope arrays distributed on a hexagonal pattern, one that produces a non redundant coverage of the uv-plane and one that produces a redundant coverage of the uv-plane. These simulated observations are combined with traditional aperture synthesis techniques to reconstruct images and determine the accuracy of these images relative to the original ones.
  45. Encrenaz, T., Greathouse, T., Roe, H., Richter, M., Lacy, J., Bezard, B., Fouchet, T., Widemann, T., 2012, A&A, 543, A153, HDO and SO2 thermal mapping on Venus: evidence for strong SO2 variability
    We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10-12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344-1370 cm-1 range (around 7.35 m) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60-80 km). Four HDO lines and tens of SO2 lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO2 and SO2/CO2 line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H2O mixing ratio is found to be 1.5 +/-0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO2 maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO2 mixing ratio strongly varies on a timescale of 24 h. The maximum SO2 mixing ratio ranges between 75 +/-25 ppb and 125 +/-50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.
  46. Debes, J., Kilic, M., Faedi, F., Shkolnik, E., Lopez-Morales, M., Weinberger, A., Slesnick, C., West, R., 2012, ApJ, 754, 59, Detection of Weak Circumstellar Gas around the DAZ White Dwarf WD 1124-293: Evidence for the Accretion of Multiple Asteroids
    Single metal-polluted white dwarfs with no dusty disks are believed to be actively accreting metals from a circumstellar disk of gas caused by the destruction of asteroids perturbed by planetary systems. We report, for the first time, the detection of circumstellar Ca II gas in absorption around the DAZ WD 1124-293, which lacks an infrared excess. We constrain the gas to >7 R WD and <32000 AU, and estimate it to be at ~54 R WD, well within WD 1124-293's tidal disruption radius. This detection is based on several epochs of spectroscopy around the Ca II H and K lines ( = 3968 A, 3933 A) with the MIKE spectrograph on the Magellan/Clay Telescope at Las Campanas Observatory. We confirm the circumstellar nature of the gas by observing nearby sightlines and finding no evidence for gas from the local interstellar medium. Through archival data we have measured the equivalent width of the two photospheric Ca lines over a period of 11 years. We see <5%-7% epoch-to-epoch variation in equivalent widths over this time period, and no evidence for long term trends. The presence of a circumstellar gas implies a near edge-on inclination to the system, thus we place limits to short period transiting planetary companions with R > R using the Wide Angle Search for Planets survey. The presence of gas in orbit around WD 1124-293 implies that most DAZs could harbor planetary systems. Since 25%-30% of white dwarfs show metal line absorption, the dynamical process for perturbing small bodies must be robust.

    This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

  47. Rivero Gonzalez, J., Puls, J., Massey, P., Najarro, F., 2012, A&A, 543, A95, Nitrogen line spectroscopy in O-stars. III. The earliest O-stars
    Context. The classification scheme proposed by Walborn et al. (2002, AJ, 123, 2754), based primarily on the relative strengths of the N iv4058 and N iii4640 emission lines, has been used in a variety of studies to spectroscopically classify early O-type stars. Owing to the lack of a solid theoretical basis, this scheme has not yet been universally accepted though.
    Aims: We provide first theoretical predictions for the N iv4058/N iii4640 emission line ratio in dependence of various parameters, and confront these predictions with results from the analysis of a sample of early-type LMC/SMC O-stars.
    Methods: Stellar and wind parameters of our sample stars are determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the helium and nitrogen ionization balance. Corresponding synthetic spectra are calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind.
    Results: Though there is a monotonic relationship between the N iv/N iii emission line ratio and the effective temperature, all other parameters being equal, theoretical predictions indicate additional dependencies on surface gravity, mass-loss, metallicity, and, particularly, nitrogen abundance. For a given line ratio (i.e., spectral type), more enriched objects should be typically hotter. These basic predictions are confirmed by results from the alternative model atmosphere code cmfgen. The effective temperatures for the earliest O-stars, inferred from the nitrogen ionization balance, are partly considerably hotter than indicated by previous studies. Consistent with earlier results, effective temperatures increase from supergiants to dwarfs for all spectral types in the LMC. The relation between observed N iv4058/N iii4640 emission line ratio and effective temperature, for a given luminosity class, turned out to be quite monotonic for our sample stars, and to be fairly consistent with our model predictions. The scatter within a spectral sub-type is mainly produced by abundance effects.
    Conclusions: Our findings suggest that the Walborn et al. (2002, AJ, 123, 2754) classification scheme is able to provide a meaningful relation between spectral type and effective temperature, as long as it is possible to discriminate for the luminosity class. In terms of spectral morphology, this might be difficult to achieve in low-Z environments such as the SMC, owing to rather low wind-strengths. According to our predictions, the major bias of the classification scheme is due to nitrogen content, and the overall spectral type-Teff relation for low-metallicity (e.g., SMC) O-stars might be non-monotonic around O3.5/O4.

    Based on (i) observations collected at the European Southern Observatory Very Large Telescope, under programmes 68.D-0369, 171.D-0237 (FLAMES), and 67.D-0238, 70.D-0164, 074.D-0109 (UVES); (ii) observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programmes 6417, 7739, and 9412; and (iii) observations gathered with the 6.5 m Magellan telescopes at the Las Campanas Observatory, Chile.Appendices A and B are available in electronic form at http://www.aanda.org

  48. Morales-Calderon, M., Stauffer, J., Stassun, K., Vrba, F., Prato, L., Hillenbrand, L., Terebey, S., Covey, K., Rebull, L., Terndrup, D., Gutermuth, R., Song, I., Plavchan, P., Carpenter, J., Marchis, F., Garcia, E., Margheim, S., Luhman, K., Angione, J., Irwin, J., 2012, ApJ, 753, 149, YSOVAR: Six Pre-main-sequence Eclipsing Binaries in the Orion Nebula Cluster
    Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for ~2400 candidate Orion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass (1 Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 M ) and longest-period (ISOY J053505.71-052354.1, P ~ 20 days) PMS EBs currently known. In two cases (1 Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.
  49. von Braun, K., Boyajian, T., Kane, S., Hebb, L., van Belle, G., Farrington, C., Ciardi, D., Knutson, H., ten Brummelaar, T., Lopez-Morales, M., McAlister, H., Schaefer, G., Ridgway, S., Collier Cameron, A., Goldfinger, P., Turner, N., Sturmann, L., Sturmann, J., 2012, ApJ, 753, 171, The GJ 436 System: Directly Determined Astrophysical Parameters of an M Dwarf and Implications for the Transiting Hot Neptune
    The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet in a 2.6 day orbit. We present results of our interferometric measurements to directly determine the stellar diameter (R sstarf = 0.455 0.018 R ) and effective temperature (T EFF = 3416 54 K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ 436's stellar mass (M sstarf = 0.507+0.071 - 0.062 M ), stellar density (* = 5.37+0.30 - 0.27 ), planetary radius (Rp = 0.369+0.015 - 0.015 R Jupiter), and planetary mass (Mp = 0.078+0.007 - 0.008 M Jupiter), implying a mean planetary density of p = 1.55+0.12 - 0.10 Jupiter. These values are generally in good agreement with previous literature estimates based on assumed stellar mass and photometric light curve fitting. Finally, we examine the expected phase curves of the hot Neptune GJ 436b, based on various assumptions concerning the efficiency of energy redistribution in the planetary atmosphere, and find that it could be constrained with Spitzer monitoring observations.
  50. Buie, M., Tholen, D., Grundy, W., 2012, AJ, 144, 15, The Orbit of Charon is Circular
    We present a detailed analysis of the orbit of Charon where we show its orbit to be circular. This analysis explores the effects of surface albedo variations on the astrometry and the resulting errors in the orbital elements. We present two new epochs of data from the Hubble Space Telescope taken in 2008 and 2010 and combine that with a re-analysis of previously published data from 1992 and 2002. Our adopted two-body Keplerian orbital elements for Charon are P = 6.3872273 0.0000003 days, a = 19573 2 km, e = 0., i = 96.218 0.008 deg, L = 4.50177 0.00018 rad, and = 3.89249 0.00012 rad for an epoch of JDT = 2452600.5 in the J2000 reference frame. The 1 upper limit to the eccentricity is 7.5 10-5. The predicted uncertainty in the position of Charon relative to Pluto at the time of the New Horizons encounter based on this orbit is 8 km.
  51. Levesque, E., Massey, P., 2012, AJ, 144, 2, Spectral Types of Red Supergiants in NGC 6822 and the Wolf-Lundmark-Melotte Galaxy
    We present moderate-resolution spectroscopic observations of red supergiants (RSGs) in the low-metallicity Local Group galaxies NGC 6822 (Z = 0.4 Z ) and Wolf-Lundmark-Melotte (WLM; Z = 0.1 Z ). By combining these observations with reduction techniques for multislit data reduction and flux calibration, we are able to analyze spectroscopic data of 16 RSGs in NGC 6822 and spectrophotometric data of 11 RSGs in WLM. Using these observations, we determine spectral types for these massive stars, comparing them to Milky Way and Magellanic Cloud RSGs and thus extending observational evidence of the abundance-dependent shift of RSG spectral types to lower metallicities. In addition, we have uncovered two RSGs with unusually late spectral types (J000158.14-152332.2 in WLM, with a spectral type of M3 I, and J194453.46-144552.6 in NGC 6822, with a spectral type of M4.5 I) and a third RSG (J194449.96-144333.5 in NGC 6822) whose spectral type has varied from an M2.5 in 1997 to a K5 in 2008. All three of these stars could potentially be members of a recently discovered class of extreme RSG variables.

    This paper is based on data gathered with the 6.5 m Magellan telescopes located at Las Campanas, Chile.

  52. Fares, R., Donati, J., Moutou, C., Jardine, M., Cameron, A., Lanza, A., Bohlender, D., Dieters, S., Martinez Fiorenzano, A., Maggio, A., Pagano, I., Shkolnik, E., 2012, MNRAS, 423, 1006, Magnetic field, differential rotation and activity of the hot-Jupiter-hosting star HD 179949
    HD 179949 is an F8V star, orbited by a giant planet at 8 R every 3.092 514 d. The system was reported to undergo episodes of stellar activity enhancement modulated by the orbital period, interpreted as caused by star-planet interactions (SPIs). One possible cause of SPIs is the large-scale magnetic field of the host star in which the close-in giant planet orbits.

    In this paper we present spectropolarimetric observations of HD 179949 during two observing campaigns (2009 September and 2007 June). We detect a weak large-scale magnetic field of a few gauss at the surface of the star. The field configuration is mainly poloidal at both observing epochs. The star is found to rotate differentially, with a surface rotation shear of d= 0.216 0.061 rad d-1, corresponding to equatorial and polar rotation periods of 7.62 0.07 and 10.3 0.8 d, respectively. The coronal field estimated by extrapolating the surface maps resembles a dipole tilted at 70. We also find that the chromospheric activity of HD 179949 is mainly modulated by the rotation of the star, with two clear maxima per rotation period as expected from a highly tilted magnetosphere. In 2009 September, we find that the activity of HD 179949 shows hints of low-amplitude fluctuations with a period close to the beat period of the system.

  53. Georgy, C., Ekstrom, S., Meynet, G., Massey, P., Levesque, E., Hirschi, R., Eggenberger, P., Maeder, A., 2012, A&A, 542, A29, Grids of stellar models with rotation. II. WR populations and supernovae/GRB progenitors at Z = 0.014
    Context. In recent years, many very interesting observations have appeared concerning the positions of Wolf-Rayet (WR) stars in the Hertzsprung-Russell diagram (HRD), the number ratios of WR stars, the nature of Type Ibc supernova (SN) progenitors, long and soft gamma ray bursts (LGRB), and the frequency of these various types of explosive events. These observations represent key constraints on massive star evolution.
    Aims: We study, in the framework of the single-star evolutionary scenario, how rotation modifies the evolution of a given initial mass star towards the WR phase and how it impacts the rates of Type Ibc SNe. We also discuss the initial conditions required to obtain collapsars and LGRB.
    Methods: We used a recent grid of stellar models computed with and without rotation to make predictions concerning the WR populations and the frequency of different types of core-collapse SNe. Current rotating models were checked to provide good fits to the following features: solar luminosity and radius at the solar age, main-sequence width, red-giant and red-supergiant (RSG) positions in the HRD, surface abundances, and rotational velocities.
    Results: Rotating stellar models predict that about half of the observed WR stars and at least half of the Type Ibc SNe may be produced through the single-star evolution channel. Rotation increases the duration of the WNL and WNC phases, while reducing those of the WNE and WC phases, as was already shown in previous works. Rotation increases the frequency of Type Ic SNe. The upper mass limit for Type II-P SNe is ~19.0 M for the non rotating models and ~16.8 M for the rotating ones. Both values agree with observations. Moreover, present rotating models provide a very good fit to the progenitor of SN 2008ax. We discuss future directions of research for further improving the agreement between the models and the observations. We conclude that the mass-loss rates in the WNL and RSG phases are probably underestimated at present. We show that up to an initial mass of 40 M, a surface magnetic field inferior to about 200 G may be sufficient to produce some braking. Much lower values are needed at the red supergiant stage. We suggest that the presence/absence of any magnetic braking effect may play a key role in questions regarding rotation rates of young pulsars and the evolution leading to LGRBs.
  54. Jensen, A., Redfield, S., Endl, M., Cochran, W., Koesterke, L., Barman, T., 2012, ApJ, 751, 86, A Detection of H in an Exoplanetary Exosphere
    We report on a search for H absorption in four exoplanets. Strong features at H are observed in the transmission spectra of both HD 189733b and HD 209458b. We attempt to characterize and remove the effects of stellar variability in HD 189733b, and along with an empirical Monte Carlo test the results imply a statistically significant transit-dependent feature of (- 8.72 1.48) 10-4 integrated over a 16 A band relative to the adjacent continuum. We interpret this as the first detection of this line in an exoplanetary atmosphere. A previous detection of Ly in HD 189733b's atmosphere allows us to calculate an excitation temperature for hydrogen, T exc = 2.6 104 K. This calculation depends significantly on certain simplifying assumptions. We explore these assumptions and argue that T exc is very likely much greater than the radiative equilibrium temperature (the temperature the planet is assumed to be at based on stellar radiation and the planetary distance) of HD 189733b. A large T exc implies a very low density that is not in thermodynamic equilibrium with the planet's lower atmosphere. We argue that the n = 2 hydrogen required to cause H absorption in the atmosphere is created as a result of the greater UV flux at HD 189733b, which has the smallest orbit and most chromospherically active central star in our sample. Though the overall integration of HD 209458b's transmission spectrum over a wide band is consistent with zero, it contains a dramatic, statistically significant feature in the transmission spectrum with reflectional symmetry. We discuss possible physical processes that could cause this feature. Our remaining two targets (HD 147506b and HD 149026b) do not show any clear features, so we place upper limits on their H absorption levels.
  55. Stansberry, J., Grundy, W., Mueller, M., Benecchi, S., Rieke, G., Noll, K., Buie, M., Levison, H., Porter, S., Roe, H., 2012, Icar, 219, 676, Physical properties of trans-neptunian binaries (120347) Salacia-Actaea and (42355) Typhon-Echidna
    We report new Hubble Space Telescope and Spitzer Space Telescope results concerning the physical properties of the trans-neptunian object (TNO) binaries (120347) Salacia-Actaea (formerly 2004 SB60), and (42355) Typhon-Echidna (formerly 2002 CR46). The mass of the (120347) Salacia-Actaea system is 4.66 0.22 1020 kg. The semi-major axis, period, and eccentricity of the binary orbit are a = 5619 87 km, P = 5.49380 0.00016 days, and e = 0.0084 0.0076, respectively. In terms of the ratio of the semimajor axis to the radius of the Hill sphere, a/rH, (120347) Salacia-Actaea is the tightest TNO binary system with a known orbit. Based on hybrid Standard Thermal Model (hybrid-STM) fits to the data, the effective diameter and V-band geometric albedo of the system are D = 954 109 km (making it one of the largest known TNOs), and pV=3.57-0.72+1.03%. Thermophysical models for (120347) Salacia suggest that it probably has a thermal inertia 5 J m-2 s-1/2 K-1, although we cannot rule out values as high as 30 J m-2 s-1/2 K-1. Based on the magnitude difference between Salacia and Actaea, = 2.37 0.06, we estimate their individual diameters to be d1 = 905 103 km and d2 = 303 35 km. The mass density of the components is =1.16-0.36+0.59 g/cm3. Hybrid-STM fits to new Spitzer data for Typhon-Echidna give an effective diameter and V-band geometric albedo for the system of D = 157 34 km, and pV=6.00-2.08+4.10%. Thermophysical models for (42355) Typhon suggest somewhat lower albedos (probably no higher than about 8.2%, as compared to the hybrid-STM upper limit of 10.1%). Taken together with the previously reported mass, this diameter indicates a density of =0.60-0.29+0.72g/cm3, consistent with the very low densities of most other TNOs smaller than 500 km diameter. Both objects must have significant amounts of void space in their interiors, particularly if they contain silicates as well as water-ice (as is expected). The ensemble of binary-TNO densities suggests a trend of increasing density with size, with objects smaller than 400 km diameter all having densities less than 1 g/cm3, and those with diameters greater than 800 km all having densities greater than 1 g/cm3. If the eccentricity of the binary orbit of (42355) Typhon-Echidna is not due to recent perturbations, considerations of tidal evolution suggest that (42355) Typhon-Echidna must have a rigidity close to that of solid water ice, otherwise the orbital eccentricity of the system would have been damped by now.
  56. Roe, H., Grundy, W., 2012, Icar, 219, 733, Buoyancy of ice in the CH4-N2 system
    In an initial laboratory exploration of the CH4 + N2 system we demonstrate that under equilibrium conditions ice will float when the molar percentage abundance of N2 in the liquid is 15.
  57. Grundy, W., 2012, ocpd, 13, Resolved Binaries in the Kuiper Belt: Optimally Scheduling Observations For Orbit Determination
    No abstract found.
  58. Roe, H., 2012, AREPS, 40, 355, Titan's Methane Weather
    Conditions in Titan's troposphere are near the triple point of methane, the second most abundant component of its atmosphere. Our understanding of Titan's lower atmosphere has shifted considerably in the past decade. Ground-based observations, Hubble Space Telescope images, and data returned from the Cassini and Huygens spacecraft show that Titan's troposphere hosts a methane-based meteorology in direct analogy to the water-based meteorology of Earth. What once was thought to be a quiescent place, lacking in clouds or localized weather and changing only subtly on long seasonal timescales, is now understood to be a dynamic system with significant weather events regularly occurring against the backdrop of dramatic seasonal changes. Although the observational record of Titan's weather covers only a third of its 30-year seasonal cycle, Titan's atmospheric processes appear to be more closely analogous to those of Earth than to those of any other object in our solar system.
  59. Tegler, S., Grundy, W., Olkin, C., Young, L., Romanishin, W., Cornelison, D., Khodadadkouchaki, R., 2012, ApJ, 751, 76, Ice Mineralogy across and into the Surfaces of Pluto, Triton, and Eris
    We present three near-infrared spectra of Pluto taken with the Infrared Telescope Facility and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phasesone highly diluted by nitrogen and the other rich in methane. For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1% 0.5%, 7.1% 0.4%, and 8.2% 0.3% for sub-Earth longitudes of 10, 125, and 257. Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. For Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0% 0.1% and 5.3% 0.4% for sub-Earth longitudes of 138 and 314. Application of the Wilcoxon rank sum test to our measurements finds the differences are not statistically significant. For Eris, we find a bulk, hemisphere-averaged, methane abundance of 10% 2%. Pluto, Triton, and Eris do not exhibit a trend in methane-nitrogen mixing ratio with depth into their surfaces over the few centimeter range probed by these observations. This result is contrary to the expectation that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth.
  60. Oszkiewicz, D., Bowell, E., Wasserman, L., Muinonen, K., Penttila, A., Pieniluoma, T., Trilling, D., Thomas, C., 2012, Icar, 219, 283, Asteroid taxonomic signatures from photometric phase curves
    We explore the correlation between an asteroid's taxonomy and photometric phase curve using the H, G12 photometric phase function, with the shape of the phase function described by the single parameter G12. We explore the usability of G12 in taxonomic classification for individual objects, asteroid families, and dynamical groups. We conclude that the mean values of G12 for the considered taxonomic complexes are statistically different, and also discuss the overall shape of the G12 distribution for each taxonomic complex. Based on the values of G12 for about half a million asteroids, we compute the probabilities of C, S, and X complex membership for each asteroid. For an individual asteroid, these probabilities are rather evenly distributed over all of the complexes, thus preventing meaningful classification. We then present and discuss the G12 distributions for asteroid families, and predict the taxonomic complex preponderance for asteroid families given the distribution of G12 in each family. For certain asteroid families, the probabilistic prediction of taxonomic complex preponderance can clearly be made. In particular, the C complex preponderant families are the easiest to detect, the Dora and Themis families being prime examples of such families. We continue by presenting the G12-based distribution of taxonomic complexes throughout the main asteroid belt in the proper element phase space. The Nysa-Polana family shows two distinct regions in the proper element space with different G12 values dominating in each region. We conclude that the G12-based probabilistic distribution of taxonomic complexes through the main belt agrees with the general view of C complex asteroid proportion increasing towards the outer belt. We conclude that the G12 photometric parameter cannot be used in determining taxonomic complex for individual asteroids, but it can be utilized in the statistical treatment of asteroid families and different regions of the main asteroid belt.
  61. Konopacky, Q., Ghez, A., Fabrycky, D., Macintosh, B., White, R., Barman, T., Rice, E., Hallinan, G., Duchene, G., 2012, ApJ, 750, 79, Rotational Velocities of Individual Components in Very Low Mass Binaries
    We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s-1), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349-25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes lsim3.5 AU, have component v sin i values that differ by greater than 3. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A-BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A-Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349-25AB and 2MASS 0746+20AB, are also known radio sources.
  62. Drout, M., Massey, P., Meynet, G., 2012, ApJ, 750, 97, The Yellow and Red Supergiants of M33
    Yellow and red supergiants are evolved massive stars whose numbers and locations on the Hertzsprung-Russell (H-R) diagram can provide a stringent test for models of massive star evolution. Previous studies have found large discrepancies between the relative number of yellow supergiants (YSGs) observed as a function of mass and those predicted by evolutionary models, while a disagreement between the predicted and observed locations of red supergiants (RSGs) on the H-R diagram was only recently resolved. Here, we extend these studies by examining the YSG and RSG populations of M33. Unfortunately, identifying these stars is difficult as this portion of the color-magnitude diagram is heavily contaminated by foreground dwarfs. We identify the RSGs through a combination of radial velocities and a two-color surface gravity discriminant, and after re-characterizing the rotation curve of M33 with our newly selected RSGs, we identify the YSGs through a combination of radial velocities and the strength of the O I 7774 triplet. We examine ~1300 spectra in total and identify 121 YSGs (a sample that is unbiased in luminosity above log (L/L ) ~ 4.8) and 189 RSGs. After placing these objects on the H-R diagram, we find that the latest generation of Geneva evolutionary tracks shows excellent agreement with the observed locations of our RSGs and YSGs, the observed relative number of YSGs with mass, and the observed RSG upper mass limit. These models therefore represent a drastic improvement over previous generations.

    Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. MMT telescope time was granted by NOAO, through the Telescope System Instrumentation Program (TSIP). TSIP is funded by the National Science Foundation (NSF). This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory.

  63. Nielsen, E., Liu, M., Wahhaj, Z., Biller, B., Hayward, T., Boss, A., Bowler, B., Kraus, A., Shkolnik, E., Tecza, M., Chun, M., Clarke, F., Close, L., Ftaclas, C., Hartung, M., Males, J., Reid, I., Skemer, A., Alencar, S., Burrows, A., de Gouveia Dal Pino, E., Gregorio-Hetem, J., Kuchner, M., Thatte, N., Toomey, D., 2012, ApJ, 750, 53, The Gemini NICI Planet-Finding Campaign: Discovery of a Multiple System Orbiting the Young A Star HD 1160
    We report the discovery of two low-mass companions to the young A0V star HD 1160 at projected separations of 81 5 AU (HD 1160 B) and 533 25 AU (HD 1160 C) by the Gemini NICI Planet-Finding Campaign. Very Large Telescope images of the system taken over a decade for the purpose of using HD 1160 A as a photometric calibrator confirm that both companions are physically associated. By comparing the system to members of young moving groups and open clusters with well-established ages, we estimate an age of 50+50 - 40 Myr for HD 1160 ABC. While the UVW motion of the system does not match any known moving group, the small magnitude of the space velocity is consistent with youth. Near-IR spectroscopy shows HD 1160 C to be an M3.5 0.5 star with an estimated mass of 0.22+0.03 - 0.04 M , while NIR photometry of HD 1160 B suggests a brown dwarf with a mass of 33+12 - 9 M Jup. The very small mass ratio (0.014) between the A and B components of the system is rare for A star binaries, and would represent a planetary-mass companion were HD 1160 A to be slightly less massive than the Sun.
  64. Hsieh, H., Yang, B., Haghighipour, N., Novakovic, B., Jedicke, R., Wainscoat, R., Denneau, L., Abe, S., Chen, W., Fitzsimmons, A., Granvik, M., Grav, T., Ip, W., Kaluna, H., Kinoshita, D., Kleyna, J., Knight, M., Lacerda, P., Lisse, C., Maclennan, E., Meech, K., Micheli, M., Milani, A., Pittichova, J., Schunova, E., Tholen, D., Wasserman, L., Burgett, W., Chambers, K., Heasley, J., Kaiser, N., Magnier, E., Morgan, J., Price, P., Jrgensen, U., Dominik, M., Hinse, T., Sahu, K., Snodgrass, C., 2012, AJ, 143, 104, Observational and Dynamical Characterization of Main-belt Comet P/2010 R2 (La Sagra)
    We present observations of the recently discovered comet-like main-belt object P/2010 R2 (La Sagra) obtained by Pan-STARRS1 and the Faulkes Telescope-North on Haleakala in Hawaii, the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on Mauna Kea, the Danish 1.54 m telescope (operated by the MiNDSTEp consortium) at La Silla, and the Isaac Newton Telescope on La Palma. An antisolar dust tail is observed to be present from 2010 August through 2011 February, while a dust trail aligned with the object's orbit plane is also observed from 2010 December through 2011 August. Assuming typical phase darkening behavior, P/La Sagra is seen to increase in brightness by >1 mag between 2010 August and December, suggesting that dust production is ongoing over this period. These results strongly suggest that the observed activity is cometary in nature (i.e., driven by the sublimation of volatile material), and that P/La Sagra is therefore the most recent main-belt comet to be discovered. We find an approximate absolute magnitude for the nucleus of HR = 17.9 0.2 mag, corresponding to a nucleus radius of ~0.7 km, assuming an albedo of p = 0.05. Comparing the observed scattering surface areas of the dust coma to that of the nucleus when P/La Sagra was active, we find dust-to-nucleus area ratios of Ad /AN = 30-60, comparable to those computed for fellow main-belt comets 238P/Read and P/2008 R1 (Garradd), and one to two orders of magnitude larger than for two other main-belt comets (133P/Elst-Pizarro and 176P/LINEAR). Using optical spectroscopy to search for CN emission, we do not detect any conclusive evidence of sublimation products (i.e., gas emission), finding an upper limit CN production rate of Q CN < 6 1023 mol s-1, from which we infer an H2O production rate of Q_H_2O\,{<}\,10^{26} mol s-1. Numerical simulations indicate that P/La Sagra is dynamically stable for >100 Myr, suggesting that it is likely native to its current location and that its composition is likely representative of other objects in the same region of the main belt, though the relatively close proximity of the 13:6 mean-motion resonance with Jupiter and the (3,-2,-1) three-body mean-motion resonance with Jupiter and Saturn mean that dynamical instability on larger timescales cannot be ruled out.

    Some data presented herein were obtained at the Isaac Newton Group of telescopes on La Palma as part of Program I/2010B/P14, at the Gemini Observatory under program GN-2011B-Q-17, with the Danish 1.54 m telescope at the ESO La Silla Observatory, and at the W. M. Keck Observatory. The Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration, and was made possible by the generous financial support of the W. M. Keck Foundation.

  65. Neugent, K., Massey, P., Skiff, B., Meynet, G., 2012, ApJ, 749, 177, Yellow and Red Supergiants in the Large Magellanic Cloud
    Due to their transitionary nature, yellow supergiants (YSGs) provide a critical challenge for evolutionary modeling. Previous studies within M31 and the Small Magellanic Cloud show that the Geneva evolutionary models do a poor job at predicting the lifetimes of these short-lived stars. Here, we extend this study to the Large Magellanic Cloud (LMC) while also investigating the galaxy's red supergiant (RSG) content. This task is complicated by contamination by Galactic foreground stars that color and magnitude criteria alone cannot weed out. Therefore, we use proper-motions and the LMC's large systemic radial velocity (~278 km s-1) to separate out these foreground dwarfs. After observing nearly 2000 stars, we identified 317 probable YSGs, 6 possible YSGs, and 505 probable RSGs. Foreground contamination of our YSG sample was ~80%, while that of the RSG sample was only 3%. By placing the YSGs on the Hertzsprung-Russell diagram and comparing them against the evolutionary tracks, we find that new Geneva evolutionary models do an exemplary job at predicting both the locations and the lifetimes of these transitory objects.
  66. Bailey, J., White, R., Blake, C., Charbonneau, D., Barman, T., Tanner, A., Torres, G., 2012, ApJ, 749, 16, Precise Infrared Radial Velocities from Keck/NIRSPEC and the Search for Young Planets
    We present a high-precision infrared radial velocity (RV) study of late-type stars using spectra obtained with NIRSPEC at the W. M. Keck Observatory. RV precisions of 50 m s-1 are achieved for old field mid-M dwarfs using telluric features for wavelength calibration. Using this technique, 20 young stars in the Pic (age ~ 12 Myr) and TW Hya (age ~ 8 Myr) Associations were monitored over several years to search for low-mass companions; we also included the chromospherically active field star GJ 873 (EV Lac) in this survey. Based on comparisons with previous optical observations of these young active stars, RV measurements at infrared wavelengths mitigate the RV noise caused by star spots by a factor of ~3. Nevertheless, star spot noise is still the dominant source of measurement error for young stars at 2.3 m, and limits the precision to ~77 m s-1 for the slowest rotating stars (v sin i < 6 km s-1), increasing to ~168 m s-1 for rapidly rotating stars (v sin i > 12 km s-1). The observations reveal both GJ 3305 and TWA 23 to be single-lined spectroscopic binaries; in the case of GJ 3305, the motion is likely caused by its 0farcs09 companion, identified after this survey began. The large amplitude, short-timescale variations of TWA 13A are indicative of a hot Jupiter-like companion, but the available data are insufficient to confirm this. We label it as a candidate RV variable. For the remainder of the sample, these observations exclude the presence of any "hot" (P < 3 days) companions more massive than 8 M Jup and any "warm" (P < 30 days) companions more massive than 17 M Jup, on average. Assuming an edge-on orbit for the edge-on disk system AU Mic, these observations exclude the presence of any hot Jupiters more massive than 1.8 M Jup or warm Jupiters more massive than 3.9 M Jup.
  67. Young, E., Becklin, E., Marcum, P., Roellig, T., De Buizer, J., Herter, T., Gusten, R., Dunham, E., Temi, P., Andersson, B., Backman, D., Burgdorf, M., Caroff, L., Casey, S., Davidson, J., Erickson, E., Gehrz, R., Harper, D., Harvey, P., Helton, L., Horner, S., Howard, C., Klein, R., Krabbe, A., McLean, I., Meyer, A., Miles, J., Morris, M., Reach, W., Rho, J., Richter, M., Roeser, H., Sandell, G., Sankrit, R., Savage, M., Smith, E., Shuping, R., Vacca, W., Vaillancourt, J., Wolf, J., Zinnecker, H., 2012, ApJL, 749, L17, Early Science with SOFIA, the Stratospheric Observatory For Infrared Astronomy
    The Stratospheric Observatory For Infrared Astronomy (SOFIA) is an airborne observatory consisting of a specially modified Boeing 747SP with a 2.7 m telescope, flying at altitudes as high as 13.7 km (45,000 ft). Designed to observe at wavelengths from 0.3 m to 1.6 mm, SOFIA operates above 99.8% of the water vapor that obscures much of the infrared and submillimeter. SOFIA has seven science instruments under development, including an occultation photometer, near-, mid-, and far-infrared cameras, infrared spectrometers, and heterodyne receivers. SOFIA, a joint project between NASA and the German Aerospace Center Deutsches Zentrum fur Luft und-Raumfahrt, began initial science flights in 2010 December, and has conducted 30 science flights in the subsequent year. During this early science period three instruments have flown: the mid-infrared camera FORCAST, the heterodyne spectrometer GREAT, and the occultation photometer HIPO. This Letter provides an overview of the observatory and its early performance.
  68. Weistrop, D., Nelson, C., Angione, R., Bachilla, R., Hancock, M., Kaiser, M., 2012, AJ, 143, 98, Characteristics of Star-forming Regions in the Advanced Minor-merger, Luminous Infrared Galaxy NGC 4194
    We report the results of long-slit spectroscopy at position angles 68, 131, and 164 for the minor-merger NGC 4194, a luminous infrared starburst galaxy. The mass within 1.2 kpc of the dynamical center is estimated to be 4.8 109 to 1.7 1010 M , depending on the assumed inclination to the plane of the sky. The star formation rate (SFR) in the areas sampled is 8 M yr-1. The metallicity, log(O/H) + 12, ranges from ~8.8 to >9.0 in regions of significant star formation, suggesting that the metallicity has been enhanced by the current star formation. The star-forming regions range in age from 5 to 9 Myr, with the youngest ages occurring in the regions of high SFR. Electron temperatures and the location of the spectra in emission line diagnostic diagrams suggest the presence of shock waves, presumably due to the presence of supernovae, winds from massive stars, and/or collisions of clouds due to the merger. The presence of massive stars and supernovae is consistent with the ages determined for the star-forming regions. The ages of the continua produced by the stellar population are estimated to range from 10 Myr to 5 Gyr. Much of the stellar population represented in the continua was probably formed before the merger and represents the progenitor galaxies.
  69. Massey, P., Morrell, N., Neugent, K., Penny, L., DeGioia-Eastwood, K., Gies, D., 2012, ApJ, 748, 96, Photometric and Spectroscopic Studies of Massive Binaries in the Large Magellanic Cloud. I. Introduction and Orbits for Two Detached Systems: Evidence for a Mass Discrepancy?
    The stellar mass-luminosity relation is poorly constrained by observations for high-mass stars. We describe our program to find eclipsing massive binaries in the Magellanic Clouds using photometry of regions rich in massive stars, and our spectroscopic follow-up to obtain radial velocities and orbits. Our photometric campaign identified 48 early-type periodic variables, of which only 15 (31%) were found as part of the microlensing surveys. Spectroscopy is now complete for 17 of these systems, and in this paper we present analysis of the first two, LMC 172231 and ST2-28, simple detached systems of late-type O dwarfs of relatively modest masses. Our orbit analysis yields very precise masses (~2%), and we use tomography to separate the components and determine effective temperatures by model fitting, necessary for determining accurate (0.05-0.07 dex) bolometric luminosities in combination with the light-curve analysis. Our approach allows more precise comparisons with evolutionary theory than previously possible. To our considerable surprise, we find a small, but significant, systematic discrepancy: all of the stars are slightly undermassive, by typically 11% (or overluminous by 0.2 dex) compared with that predicted by the evolutionary models. We examine our approach for systematic problems, but find no satisfactory explanation. The discrepancy is in the same sense as the long-discussed and elusive discrepancy between the masses measured from stellar atmosphere analysis with the stellar evolutionary models, and might suggest that either increased rotation or convective overshooting is needed in the models. Additional systems will be discussed in future papers of this series, and will hopefully confirm or refute this trend.

    This paper includes data gathered with the 6.5 m Magellan and 1.0 m Swope Telescopes located at Las Campanas Observatory, Chile, as well as data obtained with the SMARTS Consortium 1.3 and 1.0 m telescopes located at Cerro Tololo Inter-American Observatory, Chile.

  70. van Belle, G., 2012, A&ARv, 20, 51, Interferometric observations of rapidly rotating stars
    Optical interferometry provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Through direct observation of rotationally distorted photospheres at sub-milliarcsecond scales, we are now able to characterize latitude dependencies of stellar radius, temperature structure, and even energy transport. These detailed new views of stars are leading to revised thinking in a broad array of associated topics, such as spectroscopy, stellar evolution, and exoplanet detection. As newly advanced techniques and instrumentation mature, this topic in astronomy is poised to greatly expand in depth and influence.
  71. Bianchi, L., Efremova, B., Hodge, P., Massey, P., Olsen, K., 2012, AJ, 143, 74, A Treasury Study of Star-forming Regions in the Local Group. I. HST Photometry of Young Populations in Six Dwarf Galaxies
    We present a comprehensive study of young stellar populations in six dwarf galaxies in or near the Local Group: Phoenix, Pegasus, Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions, selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc resolution) with the WFPC2 camera on board the Hubble Space Telescope (HST) in six bandpasses from far-UV to I to detect and characterize their hot massive star content. This study is part of HST treasury survey program HST-GO-11079; the general data characteristics and reduction procedures are detailed in this paper and results are presented for the first six galaxies. From a total of 180 HST images, we provide catalogs of the multi-band stellar photometry and derive the physical parameters of massive stars by analyzing it with model-atmosphere colors. We use the results to infer ages, number of massive stars, extinction, and spatial characteristics of the young stellar populations. The hot massive star content varies largely across our galaxy sample, from an inconspicuous presence in Phoenix and Pegasus to the highest relative abundance of young massive stars in Sextans A and WLM. Albeit to a largely varying extent, most galaxies show a very young population (a few Myrs, except for Phoenix), and older ones (a few 107 years in Sextans A, Sextans B, NGC 6822, and WLM, ~108yr in Phoenix and Pegasus), suggesting discrete bursts of recent star formation in the mapped regions. The hot massive star content (indicative of the young populations) broadly correlates with the total galaxy stellar mass represented by the integrated optical magnitude, although it varies by a factor of ~3 between Sextans A, WLM, and Sextans B, which have similar MV . Extinction properties are also derived.
  72. Zhao, M., Milburn, J., Barman, T., Hinkley, S., Swain, M., Wright, J., Monnier, J., 2012, ApJL, 748, L8, Detection of KS -band Thermal Emission from WASP-3b
    We report the detection of thermal emission from the hot Jupiter WASP-3b in the KS band, using a newly developed guiding scheme for the WIRC instrument at the Palomar Hale 200 inch telescope. Our new guiding scheme has improved the telescope guiding precision by a factor of ~5-7, significantly reducing the correlated systematics in the measured light curves. This results in the detection of a secondary eclipse with depth of 0.181% 0.020% (9)a significant improvement in WIRC's photometric precision and a demonstration of the capability of Palomar/WIRC to produce high-quality measurements of exoplanetary atmospheres. Our measured eclipse depth cannot be explained by model atmospheres with heat redistribution but favors a pure radiative equilibrium case with no redistribution across the surface of the planet. Our measurement also gives an eclipse phase center of 0.5045 0.0020, corresponding to an ecos of 0.0070 0.0032. This result is consistent with a circular orbit, although it also suggests that the planet's orbit might be slightly eccentric. The possible non-zero eccentricity provides insight into the tidal circularization process of the star-planet system, but might also have been caused by a second low-mass planet in the system, as suggested by a previous transit timing variation study. More secondary eclipse observations, especially at multiple wavelengths, are necessary to determine the temperature-pressure profile of the planet's atmosphere and shed light on its orbital eccentricity.
  73. Elmegreen, B., Zhang, H., Hunter, D., 2012, ApJ, 747, 105, In-spiraling Clumps in Blue Compact Dwarf Galaxies
    Giant star formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the blue compact dwarf (BCD) phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. An additional indication that the dense central regions of BCDs are like bulges is the high ratio of the inner disk scale height to the scale length, which is comparable to 1 for four of the galaxies.
  74. Howell, S., Rowe, J., Bryson, S., Quinn, S., Marcy, G., Isaacson, H., Ciardi, D., Chaplin, W., Metcalfe, T., Monteiro, M., Appourchaux, T., Basu, S., Creevey, O., Gilliland, R., Quirion, P., Stello, D., Kjeldsen, H., Christensen-Dalsgaard, J., Elsworth, Y., Garcia, R., Houdek, G., Karoff, C., Molenda-Zakowicz, J., Thompson, M., Verner, G., Torres, G., Fressin, F., Crepp, J., Adams, E., Dupree, A., Sasselov, D., Dressing, C., Borucki, W., Koch, D., Lissauer, J., Latham, D., Buchhave, L., Gautier, T., Everett, M., Horch, E., Batalha, N., Dunham, E., Szkody, P., Silva, D., Mighell, K., Holberg, J., Ballot, J., Bedding, T., Bruntt, H., Campante, T., Handberg, R., Hekker, S., Huber, D., Mathur, S., Mosser, B., Regulo, C., White, T., Christiansen, J., Middour, C., Haas, M., Hall, J., Jenkins, J., McCaulif, S., Fanelli, M., Kulesa, C., McCarthy, D., Henze, C., 2012, ApJ, 746, 123, Kepler-21b: A 1.6 R Earth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070
    We present Kepler observations of the bright (V = 8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 R Earth object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequency-power spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34 0.06 M and 1.86 0.04 R , respectively, as well as yielding an age of 2.84 0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3) that the transit event is caused by a 1.64 0.04 R Earth exoplanet in a 2.785755 0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ~10 M Earth (2). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.

    Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology, the Mayall telescope at Kitt Peak National Observatory, and the WIYN Observatory which is a joint facility of NOAO, University of Wisconsin-Madison, Indiana University, and Yale University.

  75. Crossfield, I., Hansen, B., Barman, T., 2012, ApJ, 746, 46, Ground-based, Near-infrared Exospectroscopy. II. Tentative Detection of Emission from the Extremely Hot Jupiter WASP-12b
    We report the tentative detection of the near-infrared emission of the hot Jupiter WASP-12b with the low-resolution prism on Infrared Telescope Facility/SpeX. We find a K - H contrast color of 0.137% 0.054%, corresponding to a blackbody of temperature 2400+1500 - 500 K and consistent with previous, photometric observations. We also revisit WASP-12b's energy budget on the basis of secondary eclipse observations: the dayside luminosity is a relatively poorly constrained (2.0-4.3) 1030 erg s-1, but this still allows us to predict a day/night effective temperature contrast of 200-1000 K (assuming AB = 0). Thus, we conclude that WASP-12b probably does not have both a low albedo and low recirculation efficiency. Our results show the promise and pitfalls of using single-slit spectrographs for characterization of extrasolar planet atmospheres, and we suggest future observing techniques and instruments which could lead to further progress. Limiting systematic effects include the use of too narrow a slit on one nightwhich observers could avoid in the futureand chromatic slit losses (resulting from the variable size of the seeing disk) and variations in telluric transparencywhich observers cannot control. Single-slit observations of the type we present remain the best option for obtaining > 1.7 m spectra of transiting exoplanets in the brightest systems. Further and more precise spectroscopy is needed to better understand the atmospheric chemistry, structure, and energetics of this, and other, intensely irradiated planet.
  76. Boyajian, T., McAlister, H., van Belle, G., Gies, D., ten Brummelaar, T., von Braun, K., Farrington, C., Goldfinger, P., O'Brien, D., Parks, J., Richardson, N., Ridgway, S., Schaefer, G., Sturmann, L., Sturmann, J., Touhami, Y., Turner, N., White, R., 2012, ApJ, 746, 101, Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars
    We have executed a survey of nearby, main-sequence A-, F-, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars with an average precision of ~1.5%. We present new measures of the bolometric flux, which in turn leads to an empirical determination of the effective temperature for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale model isochrones to constrain the masses and ages of the stars. These results are compared to indirect estimates of these quantities obtained by collecting photometry of the stars and applying them to model atmospheres and evolutionary isochrones. We find that for most cases, the models overestimate the effective temperature by ~1.5%-4% when compared to our directly measured values. The overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than ~1.3 M . Additionally, we compare our measurements to a large sample of eclipsing binary stars, and excellent agreement is seen within both data sets. Finally, we present temperature relations with respect to (B - V) and (V - K) colors as well as spectral type, showing that calibration of effective temperatures with errors ~1% is now possible from interferometric angular diameters of stars.
  77. Zhang, H., Hunter, D., Elmegreen, B., Gao, Y., Schruba, A., 2012, AJ, 143, 47, Outside-in Shrinking of the Star-forming Disk of Dwarf Irregular Galaxies
    We have studied multi-band surface brightness profiles of a representative sample of 34 nearby dwarf irregular galaxies. Our data include Galaxy Evolution Explorer (GALEX) FUV/NUV, UBV, and H and Spitzer 3.6 m images. These galaxies constitute the majority of the LITTLE THINGS survey (Local Irregulars That Trace Luminosity ExtremesThe H I Nearby Galaxy Survey). By modeling the azimuthal averages of the spectral energy distributions with a complete library of star formation histories, we derived the stellar mass surface density distributions and the star formation rate averaged over three different timescales: the recent 0.1 Gyr, 1 Gyr, and a Hubble time. We find that, for ~80% (27 galaxies) of our sample galaxies, radial profiles (at least in the outer part) at shorter wavelengths, corresponding to younger stellar populations, have shorter disk scale lengths than those at longer wavelengths, corresponding to older stellar populations. This indicates that the star-forming disk has been shrinking. In addition, the radial distributions of the stellar mass surface density are well described as piece-wise exponential profiles, and ~80% of the galaxies have steeper mass profiles in the outer disk than in the inner region. The steep radial decline of the star formation rate in the outer parts compared to that in the inner disks gives a natural explanation for the down-bending stellar mass surface density profiles. Within the inner disks, our sample galaxies on average have constant ratios of recent star formation rate to stellar mass with radius. Nevertheless, ~35% (12 galaxies, among which 7 have baryonic mass lsim108 M ) of the sample exhibit negative slopes across the observed disk, which is in contrast with the so-called inside-out disk growth scenario suggested for luminous spiral galaxies. The tendency of star formation to become concentrated toward the inner disks in low-mass dwarf irregular galaxies is interpreted as a result of their susceptibility to environmental effects and regulation through stellar feedback.

    Based on data from the LITTLE THINGS Survey (D. A. Hunter et al. 2012, in preparation), funded in part by the National Science Foundation through grants AST-0707563, AST-0707426, AST-0707468, and AST-0707835 to US-based LITTLE THINGS team members and with generous support from the National Radio Astronomy Observatory.

  78. Slanger, T., Chanover, N., Sharpee, B., Bida, T., 2012, Icar, 217, 845, O/O 2 emissions in the Venus nightglow
    The oxygen green line is one of the most characteristic features in the terrestrial visible nightglow; it can be seen in the Venus nightglow, but with much greater intensity variation than in the terrestrial case. Here we synthesize our current understanding of the green line in the Venus nightglow and discuss what might be expected observationally in the rising phase of solar cycle 24.
  79. Zhao, M., Monnier, J., Swain, M., Barman, T., Hinkley, S., 2012, ApJ, 744, 122, Ground-based Detections of Thermal Emission from CoRoT-1b and WASP-12b
    We report a new detection of the H-band thermal emission of CoRoT-1b and two confirmation detections of the Ks-band thermal emission of WASP-12b at secondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth of 0.145% 0.049% with a 3 percentile between 0.033% and 0.235%. This depth is consistent with the previous conclusions that the planet has an isothermal region with inefficient heat transport from day side to night side, and has a dayside thermal inversion layer at high altitude. The two Ks-band detections of WASP-12b show a joint eclipse depth of 0.299% 0.065%. This result agrees with the measurement of Croll & collaborators, providing independent confirmation of their measurement. The repeatability of the WASP-12b measurements also validates our data analysis method. Our measurements, in addition to a number of previous results made with other telescopes, demonstrate that ground-based observations are becoming widely available for characterization of atmospheres of hot Jupiters.
  80. Horch, E., Bahi, L., Gaulin, J., Howell, S., Sherry, W., Baena Galle, R., van Altena, W., 2012, AJ, 143, 10, Speckle Observations of Binary Stars with the WIYN Telescope. VII. Measures during 2008-2009
    Five hundred thirty-one speckle measures of binary stars are reported. These data were taken mainly during the period 2008 June through 2009 October at the WIYN 3.5 m Telescope at Kitt Peak and represent the last data set of single-filter speckle observations taken in the WIYN speckle program prior to the use of the current two-channel speckle camera. The astrometric and photometric precision of these observations is consistent with previous papers in this series: we obtain a typical linear measurement uncertainty of approximately 2.5 mas, and the magnitude differences reported have typical uncertainties in the range of 0.1-0.14 mag. In combination with measures already in the literature, the data presented here permit the revision of the orbit of A 1634AB (= HIP 76041) and the first determination of visual orbital elements for HDS 1895 (= HIP 65982).

    The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.

  81. Hunter, D., Brinks, E., 2012, ASSP, 28, 261, The LITTLE THINGS Survey
    Dwarf galaxies seem so simple. Yet the processes that lead to star formation on galactic scales are poorly understood. We have, therefore, embarked on a comprehensive study of a sample of 42 dwarf irregular (dIm) galaxies spanning a range in luminosity in order to unravel the processes which govern star formation in these tiny systems. Our approach begins with assembling a complete dataset on these galaxies, tracing their stellar populations, gas content, dynamics, and star formation indicators. We have been granted 376 h of time with the VLA in the current B, C, and D array configurations to obtain deep HI-line maps of dIm galaxies with high angular and velocity resolution. We will combine these data with optical, UV, and IR data to answer the following questions: (1) What regulates cloud/star formation in tiny galaxies? (2) How is star formation occurring in the outer parts of dwarf galaxies, where the gas is gravitationally stable? (3) And, what happens to the star formation process at breaks in the exponential stellar light profiles?

    82. 81 publications and 5286 citations in 2012.

81 publications and 5286 citations total.

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