Exocomet Gas: Now You See It, Now You Don't

We present high spectral resolution observations of circumstellar gas present in the disks surrounding young (< 50 Myr old) A-type stars. By monitoring absorption due to the CaII K (3933Å), NaI D (5890Å) and CaII IR Triplet (8542Å) lines on a nightly basis we have detected significant variations in both their strength and velocity structure. This type of behavior, first seen in the exoplanet-harboring Beta Pictoris system, is thought to be due to the evaporation of gas by small planetesimals (‘exocomets’) on their grazing approach to the central star. In particular, we trace the evolution of absorption features that appear and disappear in the spectra of the A3V star 2 And (HD 217782) and the A0V star 5 Vul (HD 182919) on time-scales of hours, days and months. These observations represent the first simultaneous observations of the three afore-mentioned absorption lines in systems containing circumstellar gas and dust disks.