Discovery of a Compact Companion to a Nearby Star

Abstract

Radial velocity (RV) searches for exoplanets have surveyed many of the nearest and brightest stars for long-term velocity variations indicative of a companion body. Such surveys often detect high-amplitude velocity signatures of objects that lie outside the planetary mass regime, most commonly those of a low-mass star. Such stellar companions are frequently discarded as false-alarms to the main science goals of the survey, but high-resolution imaging techniques can be employed to either directly detect or place significant constraints on the nature of the companion object. Here, we present the discovery of a compact companion to the nearby star HD~118475. Our Anglo-Australian Telescope (AAT) RV data allow the extraction of the full Keplerian orbit of the companion, found to have a minimum mass of 0.445~$M_{\odot }$. Follow-up speckle imaging observations at the predicted time of maximum angular separation rule out a main sequence star as the source of the RV signature at the 3.3$\sigma$ significance level, implying that the companion must be a low-luminosity compact object, most likely a white dwarf. We provide an isochrone analysis combined with our data that constrain the possible inclinations of the binary orbit. We discuss the eccentric orbit of the companion in the context of tidal circularization timescales and show that non-circular orbit was likely inherited from the progenitor. Finally, we emphasize the need for utilizing such an observation method to further understand the demographics of white dwarf companions around nearby stars.

7 pages, 3 figures, 2 tables, accepted for publication in the Astrophysical Journal

References in corpus (9)

• The Gaia mission
• The Transiting Exoplanet Survey Satellite
• White Dwarf Cosmochronology in the Solar Neighborhood
• The white dwarf binary pathways survey - II. Radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR4
• The Pan-Pacific Planet Search VII: The most eccentric planet orbiting a giant star
• Simulations for Multi-Object Spectrograph Planet Surveys
• Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars
• Stellar Companions to the Exoplanet Host Stars HD 2638 and HD 164509
• Exclusion of Stellar Companions to Exoplanet Host Stars

Cited by in corpus (7)

• Self-lensing Discovery of a $0.2M_{\odot }$ White Dwarf in an Unusually Wide Orbit Around a Sun-like Star
• Detection of Planetary and Stellar Companions to Neighboring Stars via a Combination of Radial Velocity and Direct Imaging Techniques
• The Pan-Pacific Planet Search. VIII. Complete results and the occurrence rate of planets around low-luminosity giants
• Speckle Imaging Characterization of Radial Velocity Exoplanet Systems
• Dynamical Masses and Ages of Sirius-like Systems
• HST/FGS Trigonometric Parallaxes of M-dwarf Eclipsing Binaries
• Orbital Refinement and Stellar Properties for the HD 9446, HD 43691, and HD 179079 Planetary Systems