Long-Term Variability in the Wind in the Be Star λ Eridani

Details Long-Term Variability in the Wind in the Be Star λ Eridani Long-Term Variability in the Wind in the Be Star λ Eridani

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...18111909p&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #119.09; Bulletin of the American Astronomical Society, Vol. 25, p.742

Astronomy and Astrophysics

Astronomy

1

Scientific paper

lambda Eridani is an active Be star that displays recurrent episodes of fairly weak Hα emission, various identifiable types of transient activity during periods of activity and quiescence (Smith 1989, ApJS 71, 357), and a variable wind. To gain more insight into the causes(s) for episodic mass loss in Be stars, we have used archival IUE data and ground-based CCD observations from the Coude Feed and McMath telescopes at KPNO to study the variability in the wind and Hα emitting region in lambda Eri from 1983--90. During this interval of time the equivalent width of the C IV wind line varied from 1.8-3.5 Angstroms. When the wind is enhanced there is a prominent narrow component (NC) in C IV that displays an outflow velocity of 800--1000 km s(-1) and a strength up to 0.30 EWtot (most of the gain in EW of C IV is in the NC). The mass loss rate from the region producing the NC is ~ 7 times 10(-11) M_sun yr (-1) if the NC arises in a shocked annulus of height and radial thickness ~ 1R_{*} and ~ 0.1 R _{*}, respectively, ~ 1 R_{*} above the stellar surface. The observations clearly show that epochs of enhanced wind are accompanied by episodes of Hα emission. Two outbursts with good IUE and Hα coverage (1987-88) suggest that enhancement in the wind precedes the appearance of Balmer emission and that the largest outflow velocities in the wind are found prior to peak wind strength. Six discrete wind-Hα outbursts have been identified in the time interval studied and a period search code suggests a timescale of ~ 1.3 yr for the activity episodes. The duration of an individual outburst varies somewhat from 0.1--0.4 yr and the major outburst of late 1987 appeared to be double-peaked. The IUE and ground-based observations demonstrate that the variability seen in the wind and Balmer lines result from a common physical mechanism that initiates a mass loss episode. The evolution of a typical outburst in the context of the wind-compressed disk model for Be stars (J. Bjorkman 1992, PhD thesis) will be discussed. This project has been supported in part by NASA grants NSG 5422 (GJP), NAG5-1783 (CAG), and NAS5-28749 (MAS).

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