Detection of a strong transient blue-shifted absorption component in the beta Pictoris disk

We present high-resolution spectra (1.0 km s-1 FWHM) of the circumstellar Ca K line towards ß Pictoris obtained on 1997 June 19 and 20. On the former date a strong absorption component was found at a heliocentric velocity of vhelio = +8 km s-1, that is blueshifted by 14 km s-1 with respect to the main, ‘stable’, circumstellar component at vhelio = +22 km s-1. To our knowledge, this is the first detection of a blueshifted Ca II component with a strength comparable to the more frequently observed redshifted events. On the following night a blueshifted component was still present, but its strength had decreased significantly; in addition, a strong redshifted component had appeared at vhelio = +54 km s-1 which was absent on the previous night. The implications of these observations for the evaporating ‘comet’ model of spectral variations in the ß Pictoris disc are discussed