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Register a new userWhere Are The Circumbinary Planets of Contact Binaries?
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Up to present date, no circumbinary planet around contact binaries were discovered neither by transit method nor by the minima times variation, although they are known having third component stars around. We thus ask: where are the circumbinary planets of contact binaries? By considering the physical and geometrical parameters we simulated the light curves of contact binaries with possible transiting circumbinary jovian planets. It seems either the circumbinary jovian planets are not formed around contact binaries, probably due to dynamical effects of the binary and third component stars, or they are present but the discovery of such planets were not possible so far due to larger distortions then expected in the photometric data and in the minima times.
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The period changes of contact binaries obtained by the analysis of eclipse minima timing are found mostly chaotic in nature. However, they are representable by a few cyclic changes superposed on a secular change. The cyclic changes are caused most probably by the third components revolving around the contact binaries. Some typical examples of the period changes of contact binaries are presented in the present contribution.
The massive stars in the Galactic center inner arcsecond share analogous properties with the so-called Hot Jupiters. Most of these young stars have highly eccentric orbits, and were probably not formed in-situ. It has been proposed that these stars acquired their current orbits from the tidal disruption of compact massive binaries scattered toward the proximity of the central supermassive black hole. Assuming a binary star formed in a thin gaseous disk beyond 0.1 pc from the central object, we investigate the relevance of disk-satellite interactions to harden the binding energy of the binary, and to drive its inward migration. A massive, equal-mass binary star is found to become more tightly wound as it migrates inwards toward the central black hole. The migration timescale is very similar to that of a single-star satellite of the same mass. The binarys hardening is caused by the formation of spiral tails lagging the stars inside the binarys Hill radius. We show that the hardening timescale is mostly determined by the mass of gas inside the binarys Hill radius, and that it is much shorter than the migration timescale. We discuss some implications of the binarys hardening process. When the more massive (primary) components of close binaries eject most their mass through supernova explosion, their secondary stars may attain a range of eccentricities and inclinations. Such processes may provide an alternative unified scenario for the origin of the kinematic properties of the central cluster and S-stars in the Galactic center as well as the high velocity stars in the Galactic halo.
The abundance and properties of planets orbiting binary stars - circumbinary planets - are largely unknown because they are difficult to detect with currently available techniques. Results from the Kepler satellite and other studies indicate a minimum occurrence rate of circumbinary giant planets of ~10 %, yet only a handful are presently known. Here, we study the potential of ESAs Gaia mission to discover and characterise extrasolar planets orbiting nearby binary stars by detecting the binarys periodic astrometric motion caused by the orbiting planet. We expect that Gaia will discover hundreds of giant planets around binaries with FGK dwarf primaries within 200 pc of the Sun, if we assume that the giant planet mass distribution and abundance are similar around binaries and single stars. If on the other hand all circumbinary gas giants have masses lower than two Jupiter masses, we expect only four detections. Gaia is critically sensitive to the properties of giant circumbinary planets and will therefore make the detailed study of their population possible. Gaias precision is such that the distribution in mutual inclination between the binary and planetary orbital planes will be obtained. It also possesses the capacity to establish the frequency of planets across the H-R diagram, both as a function of mass and of stellar evolutionary state from pre-main sequence to stellar remnants. Gaias discoveries can reveal whether a second epoch of planetary formation occurs after the red-giant phase.
Dwarf carbon stars make up the largest fraction of carbon stars in the Galaxy with around 1200 candidates known to date primarily from the Sloan Digital Sky Survey. They either possess primordial carbon-enhancements, or are polluted by mass transfer from an evolved companion such that C/O is enhanced beyond unity. To directly test the binary hypothesis, a radial velocity monitoring survey has been carried out on 28 dwarf carbon stars, resulting in the detection of variations in 21 targets. Using Monte Carlo simulations, this detection fraction is found to be consistent with a 100% binary population and orbital periods on the order of hundreds of days. This result supports the post-mass transfer nature of dwarf carbon stars, and implies they are not likely hosts to carbon planets.
We present an analysis of eclipse timings of the post-common envelope binary NSVS 14256825, which is composed of an sdOB star and a dM star in a close orbit (P_{orb} = 0.110374 days). High-speed photometry of this system was performed between July, 2010 and August, 2012. Ten new mid-eclipse times were analyzed together with all available eclipse times in the literature. We revisited the (O-C) diagram using a linear ephemeris and verified a clear orbital period variation. On the assumption that these orbital period variations are caused by light travel time effects, the (O-C) diagram can be explained by the presence of two circumbinary bodies, even though this explanation requires a longer baseline of observations to be fully tested. The orbital periods of the best solution would be P_c ~ 3.5 years and P_d ~ 6.9 years. The corresponding projected semi-major axes would be a_c i_c ~ 1.9 AU and a_d i_d ~ 2.9 AU. The masses of the external bodies would be M_c ~ 2.9 M_{Jupiter} and M_d ~ 8.1 M_{Jupiter}, if we assume their orbits are coplanar with the close binary. Therefore NSVS 14256825 might be composed of a close binary with two circumbinary planets, though the orbital period variations is still open to other interpretations.
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