Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems

TL;DR

This study investigates stellar companions in 131 exoplanet systems, revealing that at least 23% have stellar companions, including new discoveries, and that planets can exist in diverse stellar environments including binaries and triples.

Contribution

It provides the first comprehensive assessment of stellar multiplicity in all known radial-velocity exoplanet systems as of 2005, including new companion discoveries and catalog verifications.

Findings

At least 23% of systems have stellar companions.

Discovered new stellar companions to HD 38529 and HD 188015.

Found evidence that some catalog entries are not gravitationally bound.

Abstract

We present results of a reconnaissance for stellar companions to all 131 radial-velocity-detected candidate extrasolar planetary systems known as of July 1, 2005. CPM companions were investigated using the multi-epoch DSS images, and confirmed by matching the trigonometric parallax distances of the primaries to companion distances estimated photometrically. We also attempt to confirm or refute companions listed in the Washington Double Star Catalog, the Catalogs of Nearby Stars, in Hipparcos results, and in Duquennoy & Mayor (1991). Our findings indicate that a lower limit of 30 (23%) of the 131 exoplanet systems have stellar companions. We report new stellar companions to HD 38529 and HD 188015, and a new candidate companion to HD 169830. We confirm many previously reported stellar companions, including six stars in five systems that are recognized for the first time as companions to exoplanet hosts. We have found evidence that 20 entries in the Washington Double Star Catalog are not gravitationally bound companions. At least three, and possibly five, of the exoplanet systems reside in triple star systems. Three exoplanet systems have potentially close-in stellar companions ~ 20 AU away from the primary. Finally, two of the exoplanet systems contain white dwarf companions. This comprehensive assessment of exoplanet systems indicates that solar systems are found in a variety of stellar multiplicity environments - singles, binaries, and triples; and that planets survive the post-main-sequence evolution of companion stars.