HS 0705+6700: A new eclipsing sdB binary

Abstract

Abstract. We report the discovery of an eclipsing binary -HS 0705+6700 -being an sdB star with a faint companion. From its light curve the orbital period of 8263.87 s, the mass ratio of the system q = 0.28, the inclination of 84.• 4 and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semi-amplitude of the radial velocity curve K1 = 85.8 km s −1 and a mass function of f (m) = 0.00626 M are determined. A spectroscopic analysis of the blue spectra results in T eff = 28 800 K, log g = 5.40, and log(nHe/nH) = −2.68. These characteristics are typical for sdB stars, as is its mass of 0.48 M . According to its mass (0.13 M ) and radius (0.19 R ), the companion is an M dwarf. The primary is in a core helium burning phase of evolution, and the system must have gone through a common envelope stage when the primary was near the tip of the red giant branch.

Origin of apparent period variations in eclipsing post-common-envelope binaries

“…HS 0705+6700 is an sdB+dM binary discovered to be a detached short-period eclipsing system by Drechsel et al (2001). Qian et al (2009b) (Drechsel et al 2001;Niarchos et al 2003;Németh et al 2005;Kruspe et al 2007).…”

The quest for companions to post-common envelope binaries

“…The residuals of the individual new timings from the elliptic orbit fit are quoted in Table 1. The amplitude of the O-C lin,2 variation, K 3 59 s, suggests a mass of the third body of M 3 12 M Jup , if we adopt a total mass of the binary of 0.62 M , which is similar to those of HS0705 (0.617 M , Drechsel et al 2001) and HW Vir (0.627 M , Lee et al 2009). The value of M 3 varies with the uncertain orbital period P 3 as P −2/3 3 and increases with the unknown inclination i 3 of the third body as 1/sin i 3 .…”

“…Early coverage of HS0705 and NSVS1425 is available from archival data of the Northern Sky Variability Survey (Woźniak et al 2004) 1 , which provides short glimpses of the sky for an extended period of time in 1999, with exposure times between 20 and 80 s. HS0705 was extensively studied from October 2000 on by Drechsel et al (2001). The source was subsequently monitored by Qian et al (2009Qian et al ( , 2010a, and references therein).…”

“…The amplitude of the light-time effect produced by the third body is K 3 = 86 ± 1 s, its orbital period is P 3 = 8.41 ± 0.05 yr, and (Drechsel et al 2001), the semi-major axis of the third object is 3.52 AU and its mass is M 3 = (31.5 ± 1.0)/sin i 3 M Jup , very similar to the values quoted by Qian et al (2010a). This mass is significantly lower than the estimate of Çamurdan et al (2012).…”

“…The 14.7 mag star HS 0705+6700 (in short HS0705) was discovered by Drechsel et al (2001) to be an eclipsing close binary with an orbital period of 2.3 h, consisting of an sdB primary and an M-dwarf secondary. Qian et al (2009Qian et al ( , 2010a summarized all the then available eclipse times and, fitting a sinusoidal to the data, suggested the presence of a brown dwarf orbiting the binary with a period of 7.15 yr.…”