We have determined a dynamical mass for the companion to HD 33636 which indicates it is a low-mass star instead of an exoplanet. Our result is based on an analysis of Hubble Space Telescope (HST) astrometry and ground-based radial velocity data. We have obtained high-cadence radial velocity measurements spanning 1.3 years of HD 33636 with the Hobby-Eberly Telescope at McDonald Observatory. We combined these data with previously published velocities to create a data set that spans nine years. We used this data set to search for, and place mass limits on, the existence of additional companions in the HD 33636 system. Our high-precision astrometric observations of the system with the HST Fine Guidance Sensor 1r span 1.2 years. We simultaneously modeled the radial velocity and astrometry data to determine the parallax, proper motion, and perturbation orbit parameters of HD 33636. Our derived parallax, pi = 35.6 +/- 0.2 mas, agrees within the uncertainties with the Hipparcos value. We find a perturbation period P = 2117.3 +/- 0.8 days, semimajor axis a_A = 14.2 +/- 0.2 mas, and system inclination i = 4.1 +/- 0.1 deg. Assuming the mass of the primary star M_A = 1.02 +/- 0.03 M_sun, we obtain a companion mass M_B = 142 +/- 11 M_jup = 0.14 +/- 0.01 M_sun. The much larger true mass of the companion relative to its minimum mass estimated from the spectroscopic orbit parameters (M sin i = 9.3 M_jup) is due to the near face-on orbit orientation. This result demonstrates the value of follow-up astrometric observations to determine the true masses of exoplanet candidates detected with the radial velocity method.
Interferometric Astrometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: Detection Limits for sub-Stellar Companions
Interferometric Astrometry of the Low-mass Binary Gl 791.2 (= HU Del) Using Hubble Space Telescope Fine Guidance Sensor 3: Parallax and Component Masses
The orbits of the quadruple star system 88 Tau A from PHASES differential astrometry and radial velocity
我们使用了Palomar高精度天体测量搜索系外行星系统项目的高精度差分天体测量和涵盖20年时间跨度的径向速度测量来确定88 Tau A系统的轨道参数。金牛座88是一个复杂的多星系统，共有6颗恒星;我们研究了其中最亮的4颗，由两对短周期恒星组成，它们的轨道周期为18年。我们提出的第一个轨道解的短周期对之一，并确定组件的质量和距离系统的百分之几的水平。此外，我们的天体测量使我们能够首次确定轨道的相互倾斜。我们发现子系统是不共面的。
Interferometric Astrometry of the Detached White Dwarf - M Dwarf Binary Feige 24 Using Hubble Space Telescope Fine Guidance Sensor 3: White Dwarf Radius and Component Mass Estimates
Ground-Based CCD Astrometry with Wide Field Imagers. I. [Observations just a few years apart allow decontamination of field objects from members in two Globular clusters.]
