Detection of a tertiary brown dwarf companion in the sdB-type eclipsing binary HS 0705+6700

Details Detection of a tertiary brown dwarf companion in the sdB-type eclipsing binary HS 0705+6700 Detection of a tertiary brown dwarf companion in the sdB-type eclipsing binary HS 0705+6700

2009-03-07

arxiv.org/abs/0903.1357v2

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

10 pages, 3 figures To be published in Astrophysical Journal

Scientific paper

10.1088/0004-637X/695/2/L163

HS 0705+6700 is a short-period (P=2.3 hours), close binary containing a hot sdB-type primary and a fully convective secondary. We have monitored this eclipsing binary for more than 2 years and as a result, 32 times of light minimum were obtained. Based on our new eclipse times together with these compiled from the literature, it is discovered that the O-C curve of HS 0705+6700 shows a cyclic variation with a period of 7.15 years and a semiamplitude of 92.4 s. The periodic change was analyzed for the light-travel time effect that may be due to the presence of a tertiary companion. The mass of the third body is determined to be M3 sin i = 0.0377 (+/-0.0043) Msun when a total mass of 0.617 Msun for HS 0705+6700 is adopted. For orbital inclinations i >= 32.8, the mass of the tertiary component would be below the stable hydrogen-burning limit of M3~0.072 Msun, and thus it would be a brown dwarf. The third body is orbiting the sdB-type binary at a distance shorter than 3.6 astronomical units (AU). HS 0705+6700 was formed through the evolution of a common envelope after the primary becomes a red giant. The detection of a sub-stellar companion in HS 0705+6700 system at this distance from the binary could give some constraints on stellar evolution in such systems and the interactions between red giants and their companions.

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