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Post Info TOPIC: NSVS 14256825
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RE: NSVS 14256825
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Title: Is there a circumbinary planet around NSVS 14256825?
Author: Ilham Nasiroglu, Krzysztof Gozdziewski, Aga Slowikowska, Krzysztof Krzeszowski, Michal Zejmo, Staszek Zola, Huseyin Er, Waldemar Ogloza, Marek Drozdz, Dorota Koziel-Wierzbowska, Bartlomiej Debski, Nazil Karaman

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-Rodono 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 (~ 0.175) with the period of ~ 10 years. Our analysis rules out two planets model proposed earlier.

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Blobrana


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Title: On the dynamical stability of the proposed planetary system orbiting NSVS 14256825
Authors: Robert A. Wittenmyer, Jonathan Horner, Jonathan Marshall

We present a detailed dynamical analysis of the orbital stability of the two circumbinary planets recently proposed to orbit the evolved eclipsing binary star system NSVS 14256825. As is the case for other recently proposed circumbinary planetary systems detected through the timing of mutual eclipses between the central binary stars, the proposed planets do not stand up to dynamical scrutiny. The proposed orbits for the two planets are extremely unstable on timescales of less than a thousand years, regardless of the mutual inclination between the planetary orbits. For the scenario where the planetary orbits are coplanar, a small region of moderate stability was observed, featuring orbits that were somewhat protected from destabilisation by the influence of mutual 2:1 mean-motion resonance between the orbits of the planets. Even in this stable region, however, the systems tested typically only survived on timescales of order 1 million years, far shorter than the age of the system.
Our results suggest that, if there are planets in the NSVS 14256825 system, they must move on orbits dramatically different to those proposed in the discovery work. More observations are clearly critically required in order to constrain the nature of the suggested orbital bodies.

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Blobrana


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Title: A photometric and spectroscopic study of NSVS 14256825: the second sdOB+dM eclipsing binary
Authors: L. A. Almeida, F. Jablonski, J. Tello, C. V. Rodrigues

We present an analysis of UBVR_{C}I_{C}JH photometry and phase-resolved optical spectroscopy of NSVS 14256825, an HW Vir type binary. The members of this class consist of a hot subdwarf and a main-sequence low-mass star in a close orbit (P_{orb} ~ 0.1 d). Using the primary-eclipse timings, we refine the ephemeris for the system, which has an orbital period of 0.11037 d. From the spectroscopic data analysis, we derive the effective temperature, T_1 = 40000 ±500 K, the surface gravity, \log g_1 = 5.50 ±0.05, and the helium abundance, n(He)/n(H)=0.003 ±0.001, for the hot component. Simultaneously modelling the photometric and spectroscopic data using the Wilson-Devinney code, we obtain the geometrical and physical parameters of NSVS 14256825. Using the fitted orbital inclination and mass ratio (i = 82\fdg5 ±0\fdg3 and q = M_2/M_1 = 0.260 ±0.012, respectively), the components of the system have M_1 = 0.419 ±0.070 solar masses, R_1 = 0.188 ±0.010 solar radii, M_2 = 0.109 ±0.023 solar masses, and R_2 = 0.162 ±0.008 solar radii. From its spectral characteristics, the hot star is classified as an sdOB star.

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