Orbital period investigation of some short-period sdB-type eclipsing binaries

Abstract

To understand the properties of orbital period changes of four short period sdB-type eclipsing binaries, HW Vir, HS 0705 + 6700, HS 2231 + 2441, and NSVS 14256825, we have monitored them photometrically since 2006. Apart from HW Vir, it is found that the O-C diagrams of HS 0705 + 6700 and HS 2231 + 2441 can also be described by a cyclic variation superimposed on a downward parabolic curve, indicating a long-term period decrease in the two systems. Therefore, of the four binary systems, longterm period variations have been detected for three ones that can be explained by magnetic braking of the fully convective component stars. This may drive these systems to evolution into normal cataclysmic variables. As for the cyclic period variations observed in the four systems, the light-travel time effect via the presence of a tertiary component is the most possible mechanism to interpret the periodic change, which reveals the presence of extremely low-mass objects

The quest for stable circumbinary companions to post-common envelope sdB eclipsing binaries

“…As noted by Lohr et al (2014), their early and late SuperWASP data is not in good agreement with Qian et al (2010) circumbinary hypothesis suggesting that a linear ephemeris may be more appropriate. Our new data, with minima occurring some 150s before Qian's predictions, support the conclusions of Lohr et al (2014).…”

“…Our new data, together with that from Nasiroglu et al (2017) allowed us to test the circumbinary stellar object hypothesis of Almeida et al (2013). We did not test the claims made by Qian et al (2010), who have yet to publish their parameters, nor have we tested the findings of Beuermann et al (2012) and Hinse et al (2014), where both recognised that their derived circumbinary parameters were poorly constrained. new data and all available historic data we have plotted the (O -C) residuals shown in Fig.…”

“…They determined an ephemeris and suggested this object was similar in many respects to both the prototype sdB/M-dwarf system HW Vir and HS0705+6700. Qian et al (2010) suggested that the binary period of NSVS 14256825 had a cyclical change, but did not provide any supporting evidence. Kilkenny & Koen (2012) provided a further nine times of minima and showed that the orbital period was increasing at a rate of ∼1.2x10 −12 days per orbit.…”

“…A summary of the findings of these investigators is presented in Table 3. Qian et al (2010) predicted a period of 15.7 years for a circumbinary object in a circular orbit around the binary system. However, their Eq.…”

“…Using the de-constructed data from Qian et al (2010) and our new data we have calculated both a linear and quadratic ephemeris over a time span of 12 years and find:…”