Is There a Circumbinary Planet around NSVS 14256825?

Abstract

The cyclic behaviour of (O-C) residuals of eclipse timings in the sdB+M eclipsing binary NSVS 14256825 was previously attributed to one or two Jovian-type circumbinary planets. We report 83 new eclipse timings that not only fill in the gaps in those already published but also extend the time span of the (O-C) diagram by three years. Based on the archival and our new data spanning over more than 17 years we re-examined the up to date system (O-C). The data revealed systematic, quasi-sinusoidal variation deviating from an older linear ephemeris by about 100 s. It also exhibits a maximum in the (O-C) near JD 2,456,400 that was previously unknown. We consider two most credible explanations of the (O-C) variability: the light propagation time due to the presence of an invisible companion in a distant circumbinary orbit, and magnetic cycles reshaping one of the binary components, known as the Applegate or Lanza-Rodonó effect. We found that the latter mechanism is unlikely due to the insufficient energy budget of the M-dwarf secondary. In the framework of the third-body hypothesis, we obtained meaningful constraints on the Keplerian parameters of a putative companion and its mass. Our best-fitting model indicates that the observed quasi-periodic (O-C) variability can be explained by the presence of a brown dwarf with the minimal mass of 15 Jupiter masses rather than a planet, orbiting the binary in a moderately elliptical orbit (e 0.175) with the period of ∼ 10 years. Our analysis rules out two planets model proposed earlier.

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

“…In particular the residuals of NSVS 14256825 give a very close fit to the more recent predicted parameters of Nasiroglu et al (2017). However, both systems report only one cycle of a proposed circumbinary companion and drawing firm conclusions would thus be premature.…”

“…More recently Nasiroglu et al (2017) provided 83 new eclipse timings spanning the period 2009 August to 2016 November. Including earlier data, they analysed three data sets and reported that their Dataset C, which excluded data from NSVS, All Sky Automatic Survey (ASAS) and SuperWASP, indicated a possible brown dwarf circumbinary companion.…”

“…Qian et al (2009) also recognised a periodicity in the data but they have not yet specified a value for the period. In their review of this object, Nasiroglu et al (2017) computed new circumbinary parameters and remaining open minded about its presence; they predicted a possible circumbinary brown dwarf with a period of 9.7 years. Future observations will either support the circumbinary hypothesis or provide evidence against it.…”

Searching for planets around eclipsing binary stars using timing method: NSVS 14256825

“…In this study, we present four new eclipse times (Tab. 1) that follow the trend of the (O-C) diagram shown recently by Nasiroglu et al (2017). The observations were performed at the TUBITAK National Observatory (TUG, T100) and at the Adiyaman University Observatory (ADYU60) in Turkey.…”

“…The observations were performed at the TUBITAK National Observatory (TUG, T100) and at the Adiyaman University Observatory (ADYU60) in Turkey. Nasiroglu et al (2017) presented 83 new eclipse timings of NSVS 14256825 which extended the time span of previous (O-C) diagram by three years. It is marked as grey shaded region in Fig.…”