| What's New
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Binary Stars
Hα-Emitting Sources
Phase-Referenced Imaging
Coherent Integration
Other Results
Binary Stars
θ¹ Orionis C
- Massive O7 primary
- Improved star acquisition system allows observation of V ≥ 5 binaries
- NPOI observations indicate longer period, lower eccentricity orbit
- Ref: Patience et al. 2008, ApJ, 674, L97
Algol
- First simultaneous optical (NPOI) & radio (VLBA) mas-resolution images
- Goal: absolute NPOI astrometry via image registration
contours = NPOI image over 6 hours
grayscale = 8 GHz VLBA
red dot = secondary position
- Ref: Zavala et al. 2007, AAS, 211, 5719
Hα-Emitting Sources
χ Ophiuchi
- Hα visibilities calibrated via continuum channels
- Spectroscopy from Lowell 1.1 m telescope
- Constrains full non-LTE numerical disk model
- Variation in gas density like that predicted for viscous disks
Other
- Similar analysis for other Be stars observed by NPOI (κ Dra, β Psc, υ Cyg)
- Ref: Jones et al. 2008, ApJ, 687, 598
Phase-Referenced Imaging
β Lyrae
- Visual binary & calibrator (nearly) unresolved →~ 0 interferometric phase
- Allows correction for instrumental & atmospheric phase effects & obtain
differential phases in channel containing Hα emission line
- Hα-channel phases + calibrated V²'s (incoherent integration) → complex visibilities
- Hα emission then imaged using standard radio interferometry techniques
- Images show Hα-emitting regions relative to continuum photocenter vs orbital phase
Hα Imaging of β Lyrae
- β Lyrae is an eclipsing Be star with strong Hα and HeI line emission.
- The system is composed of a giant B6-8 star that is filling its Roche lobe and
sending gas to a disk that surrounds and hides a main sequence B star.
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05/19 phase=0.24
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05/26 phase=0.78
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Hα images of β Lyrae. The green dot shows the continuum photocenter.
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β Lyrae Orbit
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- Orbit oriented along PA=68.8°, perpendicular to radio jet (Umana et al. 2000) and optical
polarization angle (Hoffman et al. 98).
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- Ref: Schmitt et al. 2009, ApJ, 691, 984
Coherent Integration
- Fringe tracking technique that imposes smooth time variation & measures
vacuum delay & atmospheric path delay
- Allows coherent integration over 30 sec NPOI observations
- Phase on each baseline not subject to the calibration uncertainty of amplitudes
→ Quantities derived from phases can be estimated accurately
Example: Diameters from visibility null
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For λ of zero-crossing:
θ(λ) = 1.22 λ/B
υ Oph: θ(0.8μm) = 2.6451 ± 0.0083
(1 part in 318)
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(Phase information for coherent integration bootstrapped from shorter baselines)
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- Ref: Jorgensen et al. 2007, AJ, 134, 1544
Other Results
Rapid Rotators
- Ref: Yoon et al. 2008, ApJ, 681, 570
- Vega's composition reanalyzed using full spectral synthesis based on Roche model derived
from NPOI observations
- Peculiar (λ Boötis-type) composition
- Rapid rotation leads to full mixing resulting in small mass and greater age
Artificial Satellites
- Interferometric detection of "glinting" GEO satellite DIRECTV-9S
- Fringe amplitude consistent with size scale ~1.3 m in E-W direction
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