HST-GHRS OBSERVATIONS OF BETA PICTORIS - ADDITIONAL EVIDENCE FOR INFALLING COMETS

Variable redshifted absorption features observed in the spectrum of be ta Pictoris have been attributed to comet-like bodies falling towards the star. The high quality data obtained in December 1992 at the unpre cedented resolution and sensitivity of the GHRS reinforces the model t hat both the changes in spectral line shapes as well as the very prese nce of C I, C IV and CO observed in the environment of beta Pic may be explained by the evaporation of several kilometer-sized bodies as the y approach the star. Because the spectrum of beta Pic varied substanti ally at the time the observations were done, and because the number of available lines in the UV is much larger than in the visible, it is p ossible to strongly confirm the proposed scenario. The observations cl early reveal and confirm three types of absorption features presenting different dynamical behaviour: i) a stable one, at the stellar radial velocity and corresponding to a permanent gaseous cloud around the st ar, ii) slowly varying ones, at modest shifts of few tens km s(-1) whi ch should be related to the evolution of the plasma near the star afte r its ejection away from the infalling bodies, and iii) the ones prese nting rapid changes at highly redshifted velocities directly produced by the infalling and evaporating bodies. The stable as well as the slo wly varying features represent a puzzle. A model for the origin of the se structures is discussed.