Large Variations in the Winds of Single Cool Giants: λ Velorum and γ Crucis

Abstract

UV spectra of the ``noncoronal'' single K supergiant λ Vel and of the single M giant γ Cru obtained with IUE and the Hubble Space Telescope at various epochs indicate that the profiles of many lines formed in the wind exhibit striking alterations in shape with time. We parameterize the wind profiles in terms of an empirical optical depth τ_emp by reflecting the red wing about line center and comparing the reflected intensity with that of the blue wing. In the λ Vel wind the terminal velocity v_∞ was found to be close to 40 km s^-1 in 1978, 1982, and 1994, but was at least 20 km s^-1 greater in 1990. The faster wind in 1990 also had a total optical depth that was a factor of 2-6 times greater than at the other epochs.

Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555, and on observations with the International Ultraviolet Explorer.