On the nature of the LBV/WR eclipsing binary system HD 5980

 

G. Koenigsberger

 

Centro de Ciencias Físicas, UNAM, Apdo. Postal 48-3, 62251 Cuernavaca, Morelos, México; (gloria@astroscu.unam.mx).

 

Received 2004 February 6
Accepted 2004 March 10.

 

ABSTRACT

HD 5980 is a multiple star system in the Small Magellanic Cloud that underwent a luminous blue variable-like eruption in 1993-1994. The erupting star (star A) forms part of a close eclipsing binary whose companion's (star B) Wolf-Rayet nature has recently been questioned. The data analyzed in this paper cover the period 1979-2002, and support the WNE classification of star B. The orbital phase-dependent variations of ultraviolet P Cygni absorption lines imply that the wind speed of star A is 1700–2200 km s^-1 and that of star B is 2600–3100 km s^-1. These allow an estimate of the wind-wind collision (WWC) shock cone geometry and line profiles from the WWC region. Given the assumed mass-loss rates, only a small fraction of the observed emission line profiles may originate in the WWC region. The star A+starB binary pair is likely the result of evolution with mass transfer and/or evolution with rapid rotation, and provides a magnificent opportunity for studying the processes that occur in massive multiple systems at the stages of stellar evolution just prior to the supernova event.

Key Words: Stars: Binaries (Eclipsing) — Stars: Individual (HD 5980) — Stars: Winds, Outflows — Stars: Wolf-Rayet — Stars: Variables (Luminous Blue Variables).

 

RESUMEN

Se presenta un análisis del sistema múltiple HD 5980 situado en la Nube Menor de Magallanes y de los efectos de la colisión entre los vientos, y se discute su posible ubicación en el diagrama H-R. Los datos analizados comprenden el período 1979-2002 y son consistentes con la clasificación original WNE de la estrella B, la compañera cercana de la estrella A que en 1993-1994 tuvo una erupción. La evolución del sistema probablemente se pueda describir utilizando trazas evolutivas que incluyan los efectos de rotación y/o el intercambio de masa.

 

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ACKNOWLEDGEMENTS

I wish to express my gratitude to J. Cantó, K. Gayley, L. Georgiev, and W. Schmutz for many fruitful discussions; to N. Walborn, O. de Marco, and L. Smith for allowing use of the 1973 digitized data; to J. Petrovic for discussing with me the new mass-transfer evolutionary models; to A. Jones for providing the photometric data of HD 5980; to S. Duffau for providing a determination of the visual magnitude of HD 5980 in 2002; to M. López for help in producing Figure 4; to A. Díaz Azuara, C. Guzmán, E. Sacristón, G. Zavala, L. Hernández, and R. García for computing support; and to the referee, G. Graefner, for his valuable comments and suggestions. This investigation made extensive use of the Multimission Archive at the Space Telescope (MAST) and the NASA Astrophysical Data System (ADS) and was supported by CONACYT grant 36569E and UNAM/DGAPA/PAPIIT grant IN118202. STScI is operated by AURA, under NASA contract NAS5-26555.

 

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