Statistics of low-mass companions to stars: Implications for their origin

One of the more significant results from observational astronomy over the p ast few years has been the detection, primarily via radial velocity studies , of low-mass companions (LMCs) to solar-like stars. The commonly held inte rpretation of these is that the majority are "extrasolar planets" whereas t he rest are brown dwarfs, the distinction made on the basis of apparent dis continuity in the distribution of M sin i for LMCs as revealed by a histogr am. We report here results from statistical analysis of M sin i, as well as of the orbital elements data for available LMCs, to test the assertion tha t 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 s trongly preferable. Overall, we find that a definitive statement asserting that LMCs population is heterogeneous is, at present, unjustified. In addit ion we compare statistics of LMCs with a compatible sample of stellar binar ies. We find a remarkable statistical similarity between these two populati ons. This similarity coupled with marked populational dissimilarity between LMCs and acknowledged planets motivates us to suggest a common origin hypo thesis for LMCs and stellar binaries as an alternative to the prevailing in terpretation. We discuss merits of such a hypothesis and indicate a possibl e scenario for the formation of LMCs.