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2025

1. Sikora, J., Rowe, J., Splinter, J., Barat, S., Dang, L., Cowan, N., Barclay, T., Colon, K., Desert, J., Kane, S., Llama, J., Shivkumar, H., Stassun, K., Quintana, E., 2025, AJ, 170, 105, Seasonal Changes in the Atmosphere of HD 80606 b Observed with JWST's NIRSpec/G395H
   Abstract

   High-eccentricity gas giant planets serve as unique laboratories for studying the thermal and chemical properties of H/He-dominated atmospheres. One of the most extreme cases is HD 80606 ba hot Jupiter orbiting a Sun-like star with an eccentricity of 0.93which experiences an increase in incident flux of nearly 3 orders of magnitude as the starplanet separation decreases from 0.88 au at apoastron to 0.03 au at periastron. We observed the planet's periastron passage using JWST's NIRSpec/G395H instrument (2.85.2 m) during a 21 hr window centered on the eclipse. We find that, as the planet passes through periastron, its emission spectrum transitions from a featureless blackbody to one in which CO, CH₄, and H₂O absorption features are visible. We detect CH₄ during postperiapse phases at 4.110.7 depending on the phase and on whether a flux offset is included to account for NRS1 detector systematics. Following periapse, H₂O and CO are also detected at 4.25.5 and 3.74.4, respectively. Furthermore, we rule out the presence of a strong temperature inversion near the IR photosphere based on the lack of obvious emission features throughout the observing window. General circulation models had predicted an inversion during periapse passage. Our study demonstrates the feasibility of studying hot Jupiter atmospheres using partial phase curves obtained with NIRSpec/G395H.

2. Brinkman, C., Weiss, L., Huber, D., Lee, R., Kolecki, J., Tenn, G., Zhang, J., Narayanan, S., Polanski, A., Dai, F., Bean, J., Beard, C., Brady, M., Brodheim, M., Brown, M., Chontos, A., Deich, W., Edelstein, J., Fulton, B., Giacalone, S., Gibson, S., Gilbert, G., Halverson, S., Handley, L., Hill, G., Holcomb, R., Holden, B., Householder, A., Howard, A., Isaacson, H., Kaye, S., Laher, R., Lanclos, K., Ong, J., Payne, J., Petigura, E., Pidhorodetska, D., Poppett, C., Roy, A., Rubenzahl, R., Saunders, N., Schwab, C., Seifahrt, A., Shaum, A., Sirk, M., Smith, C., Smith, R., Stefansson, G., Sturmer, J., Thorne, J., Turtelboom, E., Tyler, D., Valliant, J., Van Zandt, J., Walawender, J., Yee, S., Yeh, S., Zink, J., 2025, AJ, 170, 109, The Compositions of Rocky Planets in Close-in Orbits Tend to Be Earth-like
   Abstract

   Hundreds of exoplanets between 1 and 1.8 times the size of Earth have been discovered on close-in orbits. However, these planets show such a diversity in densities that some appear to be made entirely of iron, while others appear to host gaseous envelopes. To test this diversity in composition, we update the masses of five rocky exoplanets (HD 93963 A b, Kepler-10 b, Kepler-100 b, Kepler-407 b, and TOI-1444 b) and present the confirmation of a new planet (TOI-1011) using 187 high-precision radial velocities from Gemini/MAROON-X and Keck/KPF. Our updated planet masses suggest compositions closer to that of Earth than previous literature values for all planets in our sample. In particular, we report that two previously identified "super-Mercuries" (Kepler-100 b and HD 93963 A b) have lower masses that suggest less iron-rich compositions. We then compare the ratio of iron to rock-building species with the abundance ratios of those elements in their host stars. These updated planet compositions do not suggest a steep relationship between planet and host star compositions, contradictory to previous results, and suggest that planets and host stars have similar abundance ratios.

3. Vincenzi, M., Kessler, R., Shah, P., Lee, J., Davis, T., Scolnic, D., Armstrong, P., Brout, D., Camilleri, R., Chen, R., Galbany, L., Lidman, C., Moller, A., Popovic, B., Rose, B., Sako, M., Sanchez, B., Smith, M., Sullivan, M., Wiseman, P., Abbott, T., Aguena, M., Allam, S., Andrade-Oliveira, F., Bocquet, S., Brooks, D., Carnero Rosell, A., Carretero, J., da Costa, L., Pereira, M., Diehl, H., Doel, P., Everett, S., Flaugher, B., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Lahav, O., Lee, S., Marshall, J., Mena-Fernandez, J., Miquel, R., Muir, J., Myles, J., Palmese, A., Plazas Malagon, A., Porredon, A., Samuroff, S., Sanchez, E., Sanchez Cid, D., Sevilla-Noarbe, I., Suchyta, E., Tarle, G., To, C., Tucker, D., Vikram, V., Walker, A., Weaverdyck, N., Weller, J., 2025, MNRAS, 541, 2585, Comparing the DES-SN5YR and Pantheon+ SN cosmology analyses: investigation based on 'evolving dark energy or supernovae systematics'?
   Abstract

   Recent cosmological analyses measuring distances of type Ia supernovae (SNe Ia) and baryon acoustic oscillations (BAO) have all given similar hints at time-evolving dark energy. To examine whether underestimated SN Ia systematics might be driving these results, Efstathiou (2025) compared overlapping SN events between Pantheon+ and DES-SN5YR (20 per cent SNe are in common), and reported evidence for an $\sim$0.04 mag offset between the low- and high-redshift distance measurements of this subsample of events. If this offset is arbitrarily subtracted from the entire DES-SN5YR sample, the preference for evolving dark energy is reduced. In this paper, we show that this offset is mostly due to different corrections for Malmquist bias between the two samples; therefore, an object-to-object comparison can be misleading. Malmquist bias corrections differ between the two analyses for several reasons. First, DES-SN5YR used an improved model of SN Ia luminosity scatter compared to Pantheon+ but the associated scatter-model uncertainties are included in the error budget. Secondly, improvements in host mass estimates in DES-SN5YR also affected SN standardized magnitudes and their bias corrections. Thirdly, and most importantly, the selection functions of the two compilations are significantly different, hence the inferred Malmquist bias corrections. Even if the original scatter model and host properties from Pantheon+ are used instead, the evidence for evolving dark energy from CMB, DESI BAO Year 1 and DES-SN5YR is only reduced from 3.9$\sigma$ to 3.3$\sigma$, consistent with the error budget. Finally, in this investigation, we identify an underestimated systematic uncertainty related to host galaxy property uncertainties, which could increase the final DES-SN5YR error budget by 3 per cent. In conclusion, we confirm the validity of the published DES-SN5YR results.

4. Hartman, Z., van Belle, G., Lepine, S., Everett, M., Medan, I., 2025, AJ, 170, 91, Resolving the Unresolved: Using NESSI to Search for Unresolved Companions in Low-mass Disk Wide Binaries
   Abstract

   Stellar systems consisting of three or more stars are not an uncommon occurrence in the Galaxy. Nearly 50% of solar-type wide binaries with separations >1000 au are actually higher-order multiples with one component being a close binary. Additionally, the higher-order multiplicity fraction appears to be correlated with the physical separation of the widest component. These facts have motivated some of our current theories behind how the widest stellar systems formed, which can have separations on the order of or larger than protostellar cores. However, it is unclear if the correlation between wide binary separation and higher-order multiplicity extends to low-mass binaries. We present initial results of an ongoing speckle imaging survey of nearby low-mass wide binaries. We find an overall higher-order multiplicity fraction for our sample of 42.0% 10.9%. If we include systems where Gaia indicates that a companion is likely present, this fraction increases to 62.0% 14.2%. This is consistent with previous results from both higher-mass stars and a previous result for low-mass wide binaries. However, we do not detect the expected increase in higher-order multiplicity fraction with separation, as was seen with previous studies. We briefly explore why higher-order multiplicity statistics could be different in low-mass stars, and what the significance might be for models of wide binary formation.

5. Koch, E., Leroy, A., Rosolowsky, E., Chomiuk, L., Dalcanton, J., Pingel, N., Sarbadhicary, S., Stanimirovic, S., Walter, F., Archer, H., Bolatto, A., Busch, M., Chen, H., Chown, R., Corbould, H., Cronin, S., Darling, J., Do, T., Meyer, J., Eibensteiner, C., Hunter, D., Indebetouw, R., Jagannathan, P., Kepley, A., Kim, C., Kim, S., Kovacs, T., Marvil, J., Murphy, E., Murray, C., Ott, J., Pisano, D., Putman, M., Rybarczyk, D., Roman-Duval, J., Sandstrom, K., Schinnerer, E., Skillman, E., Smercina, A., Stelea, I., Strader, J., Sun, J., Tallapaneni, D., Tarantino, E., Villanueva, V., Weisz, D., Williams, T., Wong, T., 2025, ApJS, 279, 35, The Karl G. Jansky Very Large Array Local Group L-Band Survey (LGLBS)
   Abstract

   We present the Local Group L-Band Survey, a Karl G. Jansky Very Large Array (VLA) survey producing the highest-quality 21 cm and 12 GHz radio continuum images to date, for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA's spectral multiplexing power, we simultaneously survey the 21 cm line at high 0.4 km s¹ velocity resolution, the 12 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC 6822, IC 10, IC 1613, and the WolfLundmarkMelotte Galaxy, we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of <5 (1020 pc) for the 21 cm line with <10²⁰ cm² column density sensitivity, and even sharper views (<2; 510 pc) of the continuum. Targeting these nearby galaxies (D 1 Mpc) reveals a sharp, resolved view of the atomic gas, including 21 cm absorption, and continuum emission from supernova remnants and H II regions. These data sets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21 cm H I data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest-physical-resolution 21 cm observations of any external galaxies beyond the LMC and SMC.

6. Hunter, D., Zhang, H., Elmegreen, B., Castelloe, E., Ledford, H., Nisley, I., Hatano, R., 2025, AJ, 170, 76, Ultradeep Imaging of Nearby Dwarf Irregular Galaxies: Young Objects in the Far Outer Disk
   Abstract

   Ultradeep UBVI imaging of 10 nearby (7.8 Mpc) noninteracting dwarf irregular galaxies are used to examine their far outer stellar disks. The annulus between 26 mag arcsec² and 29 mag arcsec² in the V band is what we define as the far outer disk and is our focus here. Photometry of distinct objects in the far outer disks, including far-UV images, is used to determine ages of the objects in order to look for those that are young. In three of the galaxies we find objects with high-confidence ages 30 Myr. These objects are too young to have scattered into the far outer disk from the central regions. Therefore, they likely formed in situ. How star-forming gas clouds formed in the extreme environment of the outer stellar disks of dwarfs is a primary unanswered question.

6 publications and 1 citations in 2025.

6 publications and 1 citations total.