Oral title: Searching for gas in debris disks

Oral abstract: A debris disk is commonly described as a second generation circumstellar disk composed of dust grains, 
planetesimals and possibly already formed giant planets. It was long thought that debris disks were systems fully 
depleted of gas, but in the last few years the presence of gas has been detected in a handful of them. The nature of this 
gas is still under debate; it may be residual gas (leftover from earlier stages of the disk) or second generation gas 
(generated by FEBs: falling evaporating bodies), however, both possibilities would have great implications in the process 
of planet formation and evolution. An efficient way to detect this gas in debris disks is monitoring gas tracers using multi-
epoch high-resolution optical spectroscopy. A detection of gas in the line of sight of the star shows up as a very narrow 
absorption feature superposed to the photospheric absorption of lines such as Ca\,{\sc ii} or Na\,{\sc i}, which are good 
gas tracers. In the course of my thesis, I've been analysing such absorptions in a large sample of debris disks and I've 
detected several candidates with stable or variable absorption features that are likely produced by FEBs or exocomets. 
The detection of debris disks with exocometary activity implies dynamical instability in the system, which could possibly 
be linked to the presence of an already formed planet stirring/disturbing the rest of the disk. In this talk I present these 
particularly interesting objects that exhibit gas features. I discuss the properties of this gas and its implications on planet 
formation.