Analysis of Two Eclipsing Hot SubdwarfBinaries with a Low Mass Stellar and a BrownDwarf Companion

摘要

The formation of hot subdwarf stars (sdBs), which are core helium-burning stars located on the extended horizontal branch, is still not understood. Many of the known hot subdwarf stars reside in close binary systems with short orbital periods between a few hours and a few days with either M star or white dwarf companions. Common envelope ejection is the most probable formation channel. Among these, eclipsing systems are of special importance because it is possible to constrain the parameters of both components tightly by combining spectroscopic and light curve analyses. We report the discovery of two eclipsing binaries with a brown dwarf (< 0.07 M_⊙ ) and a 0.15 M_⊙late main sequence star companion in close orbits around sdB stars.