Observational Constraints on the HD 5980 Wind-Wind Collision

Abstract

Se presentan observaciones recientes del sistema m´ultiple HD 5980 ubicado en la Nube Menor de Magallanes que se complementan con los resultados de observaciones efectuadas desde los a˜nos 1950s. Encontramos que la componente Star A, que actualmente posee el espectro dominante tipo Wolf-Rayet, siempre ha sido la estrella con el viento m´as intenso. Las variaciones en los perfiles de l´ıneas en emisi´on se explican con una combinaci´on de los siguientes procesos: eclipses atmosf´ericos, emisi´on y absorci´on proveniente de la zona de interacci´on de los vientos, y ocultamiento de regiones de esta misma zona. Las observaciones de 2017-2020 indican un incremento en el nivel de actividad comparado con los a˜nos 2010-2015.

Analysis of spectral line profile variations observed over 6 decades in the WolfRayet system HD 5980 lead to the conclusion that Star A, the variable member of the system, has always dominated the wind collision zone (WCZ), contrary to suggestions that before 1994 the stronger wind belonged to its close companion, Star B. The observed variations are caused by a combination of physical occultations, wind eclipses and emission and absorption originating in the WCZ. The effects caused by the leading WCZ branch, which folds around Star B, are clearly seen as it crosses our line of sight to Star A during the secondary eclipse. These effects can inform on the WCZ velocity and density structures. We speculate that differences in line profiles at the same orbital phase but at different epochs may be linked to changes in the WCZ radiative properties. The 2017-2020 spectra indicate that HD 5980 was in a higher activity state than during 2010-2015.