DETECTION OF A STRONG TRANSIENT BLUESHIFTED ABSORPTION COMPONENT IN THE BETA-PICTORIS DISC

We present high-resolution spectra (1.0 km s(-1) FWHM) of the circumst ellar Ca K line towards beta Pictoris obtained on 1997 June 19 and 20. On the former date a strong absorption component was found at a helio centric velocity of v(helio) = +8 km s(-1), that is blueshifted by 14 km s(-1) with respect to the main, 'stable', circumstellar component a t v(helio) = +22 km s(-1). To our knowledge, this is the first detecti on of a blueshifted Ca II component with a strength comparable to the more frequently observed redshifted events. On the following night a b lueshifted component was still present, but its strength had decreased significantly; in addition, a strong redshifted component had appeare d at v(helio) = +54 km s(-1) which was absent on the previous night. T he implications of these observations for the evaporating 'comet' mode l of spectral variations in the beta Pictoris disc are discussed.