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Session 78 - Stars - Young and Old, Large and Small.
Display session, Wednesday, January 15
We have carried out a simultaneous observing campaign on the prototypical Be star \lambda Eri using ground stations and ROSAT, ASCA, IUE, and Voyager spacecrafts during the week of February-March 1995; a smaller campaign was carried out the following September. In late February \lambda Eri showed extraordinary disk-wind activity. ROSAT/HRI monitoring disclosed no large flares such as ROSAT observed in 1991 in \lambda Eri. Possible low amplitude fluctuations in the 1995 data occurred at the same time with unusual activity in H\alpha, HeI \lambda6678, HeII \lambda1640, CIII, and the CIV doublet. The helium line activity suggests that mass ejection occurred at the base of the wind. The strong CIII and CIV lines implies that shock interactions originated in the wind flow. It is not clear that the X-ray fluctuations are directly related to the increases in wind line absorption.
Within hours of the mild X-ray flux variations found by ROSAT on February 28, the Voyager UVS observed a ``ringing" that decayed over three 3-hr. cycles. The amplitude of these fluctuations was large (50%) at \lambda\lambda950-1100, decreased rapidly with wavelength, and faded to nondetection above \lambda1300. Various considerations indicate that these continuum variations were not due to an instrumentl pathology in the UVS. Rather, they appear to be due to a time-dependent flux deficit in the \lambda\lambda1250 during the minima of these cycles. We outline a scenario in which dense plasma over the star's surface is alternately heated and cooled quasi-periodically to produce the flux changes. Additional examples of this new phenomenon are needed. Amateur astronomers can make a significant contribution to the understanding of flickering in Be star light curves during their outburst phases.
We also draw attention to an increase in the emission of the H\alpha line that occurred at about the same time the FUV ringing started. This increased emission hints that \sim50,000K plasma near the star's surface can infuence the circumstellar disc some distance away by its increased Lyman continuum flux.
Program listing for Wednesday