Exocomets: A spectroscopic survey

Abstract

Context.While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be exocomets (falling evaporating bodies) aroundβPic in the early 1980s, only ∼20 stars have been reported to host exocomet-like events.Aims.We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity.Methods.We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the Ca IIK&H and Na ID lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies.Results.We detected non-photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the Ca IIand/or Na Ilines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the Ca IIK line are similar to those observed inβPic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with largervsiniis higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (λBoo-like) abundances, but this would require confirmation by expanding the sample.