期刊
ASTROPHYSICAL JOURNAL
卷 726, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/726/2/104
关键词
instrumentation: adaptive optics; methods: data analysis; stars: individual (HIP86032); techniques: image processing
资金
- NASA
- National Science Foundation [AST-0804417, 0334916, 0215793, 0520822, AST-0707927]
- US Air Force
- Cordelia Corporation, Hilary and Ethel Lipsitz, the Vincent Astor Fund
- National Aeronautics and Space Administration
- Science and Technology Facilities Council [ST/G00269X/1, ST/H00243X/1] Funding Source: researchfish
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0215793, 0334916, 0520822] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0908497] Funding Source: National Science Foundation
- STFC [ST/G00269X/1] Funding Source: UKRI
The nearby star alpha Oph (Ras Alhague) is a rapidly rotating A5IV star spinning at similar to 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(-0.37)(+0.23) M-circle dot and 0.85(-0.04)(+0.06) M-circle dot 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 a Oph B, of 0.77 +/- 0.05 M-circle dot 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 mas separation from 2012 March to May. 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.
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