Establishing Alpha Oph as a Prototype Rotator: Improved Astrometric Orbit
Sasha Hinkley, John D. Monnier, Ben R. Oppenheimer, Lewis C Roberts, Michael Ireland, Neil Zimmerman, Douglas Brenner, Ian R. Parry, Frantz Martinache, Olivier … 展开作者
Sasha Hinkley, John D. Monnier, Ben R. Oppenheimer, Lewis C Roberts, Michael Ireland, Neil Zimmerman, Douglas Brenner, Ian R. Parry, Frantz Martinache, Olivier Lai, Remi Soummer, Anand Sivaramakrishnan, Charles Beichman, Lynne Hillenbrand, Ming Zhao, James P. Lloyd, David Bernat, Gautam Vasisht, Justin R. Crepp, Laurent Pueyo, Michael Shao, Marshall D. Perrin, David L. King, Antonin Bouchez, Jennifer E. Roberts, Richard Dekany, Rick Burruss
The nearby star Alpha Oph (Ras Alhague) is a rapidly rotating A5IV star spinning at ~89% of its breakup velocity. This system has been imaged extensively by interferometric techniques, giving a precise geometric model of the star's oblateness and the resulting temperature variation on the stellar surface. Fortuitously, Alpha Oph has a previously known stellar companion, and characterization of the orbit provides an independent, dynamically-based check of both the host star and the companion mass. Such measurements are crucial to constrain models of such rapidly rotating stars. In this study, we combine eight years of Adaptive Optics imaging data from the Palomar, AEOS, and CFHT telescopes to derive an improved, astrometric characterization of the companion orbit. We also use photometry from these observations to derive a model-based estimate of the companion mass. A fit was performed on the photocenter motion of this system to extract a component mass ratio. We find masses of 2.40^{0.23}_{0.37} solar masses and 0.85^{0.06}_{0.04} solar masses for Alpha Oph A and Alpha Oph B, respectively. Previous orbital studies of this system found a mass too high for this system, inconsistent with stellar evolutionary calculations. Our measurements of the host star mass are more consistent with these evolutionary calculations, but with slightly higher uncertainties. In addition to the dynamically-derived masses, we use IJHK photometry to derive a model-based mass for Alpha Oph B, of 0.77 +/- 0.05 solar masses marginally consistent with the dynamical masses derived from our orbit. Our model fits predict a periastron passage on 2012 April 19, with the two components having a ~50 milliarcsec separation from March to May 2012. A modest amount of interferometric and radial velocity data during this period could provide a mass determination of this star at the few percent level.
A Century of Radial Velocity and Astrometric Monitoring of 70 Oph AB: New PFS Data and Constraints on Planetary Companions
University of Michigan（密歇根大学）；University of California, Riverside（加州大学河滨分校）；Carnegie Institution for Science（卡内基科学研究所）；California Institute of Technology（加州理工学院）
Modeling Multi-Wavelength Stellar Astrometry. II. Determining Absolute Inclinations, Gravity Darkening Coefficients, and Spot Parameters of Single Stars with SIM Lite
Full orbital solution and dynamical masses for a new shell-Be + sdOB binary AN Col
European Organisation for Astronomical Research in the Southern Hemisphere (ESO)（欧洲南方天文台）；Georgia State University（佐治亚州立大学）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心）；Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas（圣保罗大学，天文学、地球物理学和大气科学研究所）
