Exocomets: A spectroscopic survey^⋆

¹ Dpto. Física Teórica, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain
e-mail: isabel.rebollido@uam.es
² Observatorio Astrónomico de Calar Alto, CAHA, 04550 Gérgal, Almería, Spain
³ Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus Camino Bajo del Castillo, s/n, Villanueva de la Cañada, 28692 Madrid, Spain
⁴ INAF, Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁵ STAR Institute, Université de Liège, F.R.S.-FNRS, 19c Allée du Six Août, 4000 Liège, Belgium
⁶ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, 5030 Casilla, Valparaíso, Chile
⁷ Núcleo Milenio de Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
⁸ European Space Astronomy Centre (ESA), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁹ Université de Toulouse, UPS-OMP, IRAP, Toulouse 31400, France
¹⁰ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21212, USA
¹¹ Steward Observatory, Department of Astronomy, University of Arizona, Tucson, AZ 85721, USA
¹² Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
¹³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁴ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
¹⁵ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
¹⁶ Aurora Technology B.V. for ESA, ESA-ESAC, Villanueva de la Cañada, 28691 Madrid, Spain
¹⁷ Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain

Received: 11 June 2019
Accepted: 23 March 2020

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) around β Pic 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 II K&H and Na I D 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 II and/or Na I lines; 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 II K line are similar to those observed in β Pic. 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 larger v sin i is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (λ Boo-like) abundances, but this would require confirmation by expanding the sample.