Detecting Exoplanets in S Type Systems Around Eclipsing Binary Stars

How eclipse time variations, eclipse duration variations and radial velocities can reveal S-type planets in close eclipsing binaries 

Authors:

Oshagh et al

Abstract:

While about a dozen transiting planets have been found in wide orbits around an inner, close stellar binary (so-called P-type planets), no planet has yet been detected orbiting only one star (a so-called S-type planet) in an eclipsing binary. This is despite a large number of eclipsing binary systems discovered with the Kepler telescope. Here we propose a new detection method for these S-type planets, which uses a correlation between the stellar radial velocities (RVs), eclipse timing variations (ETVs) and eclipse duration variations (EDVs). We test the capability of this technique by simulating a realistic benchmark system and demonstrate its detectability with existing high-accuracy RV and photometry instruments. We illustrate that with a small number of RV observations, the RV–ETV diagrams allows us to distinguish between prograde and retrograde planetary orbits and also the planetary mass can be estimated if the stellar cross-correlation functions can be disentangled. We also identify a new (though minimal) contribution of S-type planets to the Rossiter–McLaughlin effect in eclipsing stellar binaries. We finally explore possible detection of exomoons around transiting luminous giant planets and find that the precision required to detect moons in the RV curves of their host planets is of the order of cm s−1 and therefore not accessible with current instruments.

CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk

CoRoT 223992193: Investigating the variability in a low-mass, pre-main sequence eclipsing binary with evidence of a circumbinary disk

Authors:

Gillen et al

Abstract:

CoRoT 223992193 is the only known low-mass, pre-main sequence eclipsing binary that shows evidence of a circumbinary disk. The system displays complex photometric and spectroscopic variability over a range of timescales and wavelengths. Using two optical CoRoT runs, and infrared Spitzer 3.6 and 4.5 μm observations (simultaneous with the second CoRoT run), we model the out-of-eclipse light curves. The large scale structure in both CoRoT light curves is consistent with the constructive and destructive interference of starspot signals at two slightly different periods. Using the stellar vsini 's, we infer different rotation periods: the primary is consistent with synchronisation and the secondary is slightly supersynchronous. Comparison of the raw data to the residuals of our spot model in colour-magnitude space indicates additional contributions consistent with variable dust emission and obscuration. We also identify short-duration flux dips preceding secondary eclipse in all three CoRoT and Spitzer bands. We construct a model of the inner regions of the binary and propose that these dips could be caused by partial occultation of the central binary by the accretion stream onto the primary star. Analysis of 15 VLT/FLAMES Hα profiles reveal an emission profile associated with each star: the majority is consistent with chromospheric emission but higher velocity emission is also seen, which could be due to prominences or accretion-related phenomena. In addition, simultaneous u and r-band observations from CFHT/MEGACam reveal a short-lived u-band excess consistent with either an accretion hot spot or stellar flare. The photometric and spectroscopic variations are complex but are consistent with the picture of two active stars possibly undergoing non-steady, low-level accretion; the system's very high inclination provides a new view of such variability.

Three Brown Dwarfs in Eclipsing Binaries Found

Substellar companions in low-mass eclipsing binaries NSVS 01286630, NSVS 02502726, and NSVS 07453183

Abstract:

Wolf et al

Abstract:

Aims.

As part of our long-term observational project we aim to measure very precise mid-eclipse times for low-mass eclipsing binaries, which are needed to accurately determine their period changes. Over two hundred new precise times of minimum light recorded with CCD were obtained for three eclipsing binaries with short orbital periods: NSVS 01286630 (), NSVS 02502726 (), and NSVS 07453183 ().

Methods.

O−C diagrams of studied stars were analysed using all reliable timings, and new parameters of the light-time effect were obtained.

Results.

We derived for the first time or improved the very short orbital periods of third bodies of between one and seven years for all measured low-mass systems. We calculated that the lowest masses of the third components are between those of red and brown dwarfs. The multiplicity of these systems also plays an important role in the precise determination of their physical parameters. This research is part of an ongoing collaboration between professional astronomers and the Czech Astronomical Society, Variable Star and Exoplanet Section.

Are Time Variations in Close Binary Systems Indicate Exoplanet Presence?

Eclipsing time variations in close binary systems: Planetary hypothesis vs. Applegate mechanism

Authors:

Völschow et al

Abstract:

The observed eclipsing time variations in post-common-envelope binaries (PCEBs) can be interpreted as potential evidence for massive Jupiter-ke planets, or as a result of magnetic activity, leading to quasi-periodic changes in the quadrupole moment of the secondary star. The latter is commonly referred to as the Applegate mechanism. Following Brinkworth et al. (2006), we employ here an improved version of Applegate's model including the angular momentum exchange between a finite shell and the core of the star. The framework is employed to derive the general conditions under which the Applegate mechanism can work, and is subsequently applied to a sample of 16 close binary systems with potential planets, including 11 PCEBs. Further, we present a detailed derivation and study of analytical models which allow for an straightforward extension to other systems. Using our full numerical framework, we show that the Applegate mechanism can clearly explain the observed eclipsing time variations in 4 of the systems, while the required energy to produce the quadrupole moment variations is too high in at least 8 systems. In the remaining 4 systems, the required energy is comparable to the available energy produced by the star, which we consider as borderline cases. Therefore, the Applegate mechanism cannot uniquely explain the observed period time variations for this entire population. Even in systems where the required energy is too high, the Applegate mechanism may provide an additional scatter, which needs to be considered in the derivation and analysis of planetary models.

Eclipsing Binary FL Lyr has a Circumbinary Jupiter Analog Gas Giant

An Exo-Jupiter Candidate in the Eclipsing Binary FL Lyr

Authors:

Kozyreva et al

Abstract:

Light curves of the eclipsing binary FL Lyr acquired by the Kepler space telescope are analyzed. Eclipse timing measurements for FL Lyr testify to the presence of a third body in the system. Preliminary estimates of its mass and orbital period are greater than 2 MJupiter and greater than 7 yrs. The times of primary minimum in the light curve of FL Lyr during the operation of the Kepler mission are presented.

Eclipsing Binary CoRoT 223992193 Appears to Have a Circumpibary Protoplanetary Disk

A circumbinary disc model for the variability of the eclipsing binary CoRoT 223992193

Authors:

Terquem et al

Abstract:

We calculate the flux received from a binary system obscured by a circumbinary disc. The disc is modelled using two dimensional hydrodynamical simulations, and the vertical structure is derived by assuming it is isothermal. The gravitational torque from the binary creates a cavity in the disc's inner parts. If the line of sight along which the system is observed has a high inclination I, it intersects the disc and some absorption is produced. As the system is not axisymmetric, the resulting light curve displays variability. We calculate the absorption and produce light curves for different values of the dust disc aspect ratio H/r and mass of dust in the cavity Mdust. This model is applied to the high inclination (I=85∘) eclipsing binary CoRoT 223992193, which shows 5-10% residual photometric variability after the eclipses and a spot model are subtracted. We find that such variations for I∼85∘ can be obtained for H/r=10−3 and Mdust≥10−12 M⊙. For higher H/r, Mdust would have to be close to this lower value and I somewhat less than 85∘. Our results show that such variability in a system where the stars are at least 90% visible at all phases can be obtained only if absorption is produced by dust located inside the cavity. If absorption is dominated by the parts of the disc located close to or beyond the edge of the cavity, the stars are significantly obscured.