Oral title: The search for Exocomets

Oral abstract: The environment of pre-main sequence (MS) stars is expected to be rapidly depleted of gas as the star 
evolves. Thus, a replenishment mechanism, i.e. exocomets, is required to explain the presence of gas recently reported 
to be present around some MS stars. Here, we present a high resolution spectroscopic survey of over 100 A to G stars,  
searching for gas in the form of stable and variable non-photospheric absorptions in metallic lines (mainly Ca II and Na I). 
The observations were carried out in both hemispheres at La Palma (Spain), La Luz (México) and La Silla (Chile) 
observatories. The over 2000 spectra obtained, allow us to construct time-series for each star and detect variations of 
the metallic absorptions as the exocomet evaporates when it approaches the star. So far, we have found gas compatible 
with circumstellar origin in almost half of the sample, and variable absorptions in several objects, being some of them 
new detections. The growing number of exocomet-bearing systems detected since the first discovery in the late 80's, will 
allow us to better understand disc evolution, and therefore planet formation.