MULTISITE CONTINUOUS SPECTROSCOPY .5. RAPID PHOTOSPHERIC VARIABILITY IN THE BE-STAR-48 PERSEI FROM THE MUSICOS 1989 CAMPAIGN

Rapid variability in the photospheric He I 6678 line of the Be star 48 Per (HD 25940, HR 1273) has been detected from 258 high S/N CCD spect ra taken with four 1.5-2.0 meter telescopes over three consecutive nig hts during the multisite spectroscopic MUSICOS 1989 campaign. 48 Per i s a rather moderate-V sin i star, known to have presented slight long- term variations in the intensity of Balmer emission lines and in the V /R ratio. It is shown that the MUSICOS 1989 observations preceded a ne w activity phase. Search for line-profile variations, hereafter Ipv, w as performed with time-series analysis using two methods (TF+CLEAN and Least-Squares) and with analysis of residuals. Weak blue-to-red and r ed-to-blue moving subfeatures with the same acceleration have been det ected in the residuals. Their presence confirms that this star is seen under a moderate angle of inclination, i similar to 40 degrees, in ag reement with estimates based on fundamental stellar parameters. A 6.04 c/d frequency, associated with the moving subfeatures mentioned above , has been firmly established from time-series analysis and correspond s more closely, in the frame of non-radial pulsations (NRP), to a tess eral mode (\m\ = l - 1 = 9 +/- 2). Two other possible frequencies (0.8 5 and 2.77 c/d) have been detected but need to be confirmed with new o bservations obtained over a longer time span. Despite additional spect ra obtained at Haute Provence Observatory, we could not confirm the pr evious value of the orbital period or the amplitude of the radial velo city,curve of 48 Per, and therefore it was premature to search for tid ally-forced oscillations.