Exocomets: A spectroscopic survey
  While exoplanets are now routinely detected, the detection of small bodies in
extrasolar systems remains challenging. Since the discovery of sporadic events
interpreted as exocomets (Falling Evaporating Bodies) around $\beta$ Pic in the
early 80s, only $\sim$20 stars have been reported to host exocomet-like events.
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. 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 have been collected in 14 observing campaigns expanding over 2 years from
both hemispheres. We have analysed the Ca ii K&H and Na i D lines in order to
search for non-photospheric absorptions originated in the circumstellar
environment, and for variable events that could be caused by outgassing of
exocomet-like bodies. We have detected non-photospheric absorptions towards 50%
of the sample, attributing a circumstellar origin to half of the detections
(i.e. 26% of the sample). Hot circumstellar gas is detected in the metallic
lines inspected via narrow stable absorptions, and/or variable
blue-/red-shifted absorption events. Such variable events were found in 18
stars in the Ca ii and/or Na i lines; 6 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 $\beta$ Pic. While we do not find a
significant trend with the age or location of the stars, we do find that the
probability of finding CS gas in stars with larger vsin i is higher. We also
find a weak trend with the presence of near-infrared excess, and with anomalous
($\lambda$ Boo-like) abundances, but this would require confirmation by
expanding the sample.
