A ~40 year variability cycle in the LBV/WR binary system HD 5980 ?
G. Koenigsberger, L. Georgiev, D.J. Hillier, N. Morrell, R. Barba' and R. Gamen
Instituto de Ciencias Fisicas, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico; Department of Astronomy, University of Pittsburg; Las Campanas Observatory, The Carnegie Observatories; Departamento de Fisica, Universidad de la Serena; Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata.
The massive Wolf-Rayet stellar system HD 5980 in the Small Magellanic Cloud entered a sudden and brief 1--3 mag eruptive state in the mid-1990s. The cause of the instability is not yet understood, but mechanisms similar to those in luminous blue variables are suspected. Using a previously unreported set of spectroscopic data obtained in 1955--1967 and recently acquired optical and HST/STIS spectra, we find that: 1) the brief eruptions of 1993 and 1994 occurred at the beginning of an extended (on the order of decades) high state of activity characterized by large emission-line intensities; 2) the level of activity is currently subsiding; and 3) another strong emission-line episode appears to have occurred between 1960--1965, suggesting the possibility that the long-term cyclical variability may be recurrent on an approximate 40 year timescale. These characteristics suggest the possible classification of HD 5980 as an S Doradus-type variable. The effects due to binary interactions in the system are discussed, and we tentatively suggest that the short duration and relatively hot spectral type (WN11/B1.5I) observed during maximum in the visual light curve may be attributed to these interactions.
Reference: AJ, 139, 2600 (2010)
Status: Manuscript has been accepted