High angular resolution imaging and infrared spectroscopy of CoRoT candidates

Abstract

Context. Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. In the case of the CoRoT space mission, the majority of the false-positives are removed by a detailed analysis of the light curves and by seeing-limited imaging in-and out-of-transit. However, the critical question is how many of the candidates that passed all these tests are false-positives. Such false-positives can be caused by eclipsing binaries, which are either related or unrelated to the targets. Aims. For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. Our aim is to search for companion candidates that had not been recognized in previous observations. Methods. We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES. Results. We found previously unknown stars within 2 of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28−35% of the remaining candidates are found to possess companions that are bright enough to be false-positives. Conclusions. Given that the companion candidates cluster around the targets and that the J − K colours are consistent with physical companions, we conclude that the companion candidates are more likely to be physical companions rather than unrelated field stars.

III.7 Planets orbiting stars more massive than the Sun

“…The aim of these observations was to find out whether there are any stars within a few arcsec from the target that are bright enought to be FPs (see Guenther et al 2013 for details on this method). We detected two previously unknown stars.…”

Friends of Hot Jupiters. Iii. An Infrared Spectroscopic Search for Low-Mass Stellar Companions

“…Bardalez Gagliuffi et al (2014) analyzed a sample of 815 M and L dwarf spectra taken with IRTF SpeX in order to locate blended stellar companions with relatively low effective temperatures (also see Burgasser et al 2010). Guenther et al (2013) used CRIRES on the Very Large Telescope to identify approximately twenty planet-hosting stars in the CoRoT sample with blended spectra from close stellar companions. Kolbl et al (2015) observed planet-hosting stars from the Kepler survey with optical Keck HIRES spectroscopy in order to search for binary companions with relative radial velocities greater than 10 km s −1 such that the secondary absorption lines are Doppler shifted.…”

A planet in a polar orbit of 1.4 solar-mass star

“…Although it has been argued that the exclusion of FPs at distances larger than 1-2 arcsec is sufficient to show that the star is the transiting object, detailed studies show that AO-imaging is essential for confirming transiting planets, otherwise the probability for FPs is unacceptably high (Guenther et al 2013 [13]). We thus obtained images with PISCES, the adaptive optics imager of the Large Binocular Telescope (LBT).…”