Eclipsing binaries and fast rotators in theKeplersample

Abstract

Context. The Kepler mission has searched for planetary transits in more than two hundred thousand stars by obtaining very accurate photometric data over a long period of time. Among the thousands of detected candidates, the planetary nature of around 15% has been established or validated by different techniques. But additional data are needed to characterize the rest of the candidates and reject other possible configurations. Aims. We started a follow-up program to validate, confirm, and characterize some of the planet candidates. In this paper we present the radial velocity analysis of those that present large variations, which are compatible with being eclipsing binaries. We also study those showing high rotational velocities, which prevents us from reaching the necessary precision to detect planetary-like objects. Methods. We present new radial velocity results for 13 Kepler objects of interest (KOIs) obtained with the CAFE spectrograph at the Calar Alto Observatory and analyze their high-spatial resolution (lucky) images obtained with AstraLux and the Kepler light curves of some interesting cases. Results. We have found five spectroscopic and eclipsing binaries (group A). Among them, the case of KOI-3853 is of particular interest. This system is a new example of the so-called heartbeat stars, showing dynamic tidal distortions in the Kepler light curve. We have also detected duration and depth variations of the eclipse. We suggest possible scenarios to explain such an effect, including the presence of a third substellar body possibly detected in our radial velocity analysis. We also provide upper mass limits to the transiting companions of six other KOIs with high rotational velocities (group B). This property prevents the radial velocity method from achieving the necessary precision to detect planetary-like masses. Finally, we analyze the large radial velocity variations of two other KOIs, which are incompatible with the presence of planetary-mass objects (group C). These objects are likely to be stellar binaries. However, a longer timespan is needed to complete their characterization.

SOPHIE velocimetry ofKeplertransit candidates

“…We thus checked the v sin i value by using the Fourier transform method (see Simón-Díaz & Herrero 2007, and reference therein). From the first zero in the Fourier transform of various isolated spectral lines in the co-added SOPHIE spectrum, we found v sin i = 66.0 ± 2.5 km s −1 and v macro = 18.1 ± 5.5 km s −1 , consistent with the value v sin i = 70.0 ± 5.0 km s −1 given by Lillo-Box et al (2015) 5 . The final value for the projected rotational velocity will be given in Sect.…”

“…2.2 are of better quality with more measurements. It is also consistent with the maximum projected mass of 25.2 M Jup determined by Lillo-Box et al (2015). We performed the same analysis assuming an eccentric orbit, setting the eccentricity to its 3σ upper limit of 0.72.…”

Search for light curve modulations amongKeplercandidates

“…Massive planets from the Exoplanet Catalogue (exoplanet.eu) are plotted as black crosses. Leftward arrows show the upper limits to the masses of the three fast rotators in Lillo-Box et al (2015). Solar metallicity isochrones of Baraffe et al (1998) are also plotted for reference as gray thick lines.…”

KOI-3890: a high-mass-ratio asteroseismic red giant+M-dwarf eclipsing binary undergoing heartbeat tidal interactions

“…The potential binary star nature of this system was first suggested in Lillo-Box et al (2015), who collected 22 radial velocities using the CAFE spectrograph (Aceituno et al 2013). While the phase coverage in Lillo-Box et al (2015) is limited, the authors place constraints on the minimum eccentricity e ≥ 0.33 and minimum radial velocity amplitude K ≥ 2.5 kms −1 , which is equivalent to a required minimum companion mass of M > 0.0097 ± 0.0014M . This minimum mass is equivalent to M > 10.2M J , and whilst this theoretically allows for a planet-mass object (M 13M J ; Burrows et al 2001) this is more likely to be a binary star system.…”