31st Annual Meeting of the DPS, October 1999
Session 5. Extra-solar Planets: Dynamics and Detection
Contributed Oral Parallel Session, Monday, October 11, 1999, 10:30am-12:00noon, Sala Kursaal

## [5.06] Statistics of Low-Mass Companions to Stars: Implicatons for Their Origin

D.C. Black, T.F. Stepinski (Lunar and Planetary Institute)

One of the more significant results from observational astronomy over the past few years has been the detection, primarily via radial velocity studies, of low-mass companions (LMCs) to solar-like stars. The commonly held interpretation of these is that the majority are extrasolar planets" whereas the rest are brown dwarfs, the distinction made on the basis of apparent discontinuity in the distribution of M \sin i for LMCs as revealed by a histogram. We report here results from formal statistical analysis of M \sin i, as well as the orbital elements data for available LMCs, to test the assertion that the LMCs population is heterogeneous. The outcome is mixed. Solely on the basis of the distribution of M \sin i a heterogeneous model is preferable, although no unique best-fit mixture can be determined. On the basis of the distribution of orbital periods and eccentricities a homogeneous model is strongly preferable. Overall, we find that a definitive statement asserting that LMCs population is heterogeneous is, at present, unjustified. In addition we compare statistics of LMCs with a compatible sample of stellar binaries. We find a remarkable statistical similarity between these two populations. This similarity coupled with marked populational dissimilarity between LMCs and acknowledged planets motivates us to suggest a common origin hypothesis for all LMCs and selected stellar binaries as an alternative to the prevailing interpretation. We discuss merits of such a hypothesis and indicate a possible scenario for the formation of LMCs.