Context. Luminous BA-type supergiants are the brightest stars in the visible that can be observed in distant galaxies and are potentially accurate distance indicators. The impact of the variability of the stellar winds on the distance determination remains poorly understood.
Aims: Our aim is to probe the inhomogeneous structures in the stellar wind using spectro-interferometric monitoring.
Methods: We present a spatially resolved, high-spectral resolution (R = 12 000) K-band temporal monitoring of the bright supergiant
Results: A systematic visibility decrease is observed across the Brγ line indicating that at a radius of about 1.25 R∗ the photospheric absorption is filled by emission from the wind. During the 2006-2007 period the Brγ and likely the continuum forming regions were larger than in the 2009-2010 epoch. Using CMFGEN we infer a mass-loss rate change of about 20% between the two epochs. We also find time variations in the differential visibilities and phases. The 2006-2007 period is characterised by noticeable variations in the differential visibilities in Doppler position and width and by weak variations in differential and closure phase. The 2009-2010 period is much quieter with virtually no detectable variations in the dispersed visibilities but a strong S-shaped signal is observed in differential phase coinciding with a strong ejection event discernible in the optical spectra. The differential phase signal that is sometimes detected is reminiscent of the signal computed from hydrodynamical models of corotating interaction regions. For some epochs the temporal evolution of the signal suggests the rotation of the circumstellar structures.
Astronomy and Astrophysics
- Pub Date:
- June 2014
- techniques: high angular resolution;
- techniques: interferometric;
- stars: mass-loss;
- stars: individual: Rigel;
- stars: rotation;
- circumstellar matter;
- Astrophysics - Solar and Stellar Astrophysics
- Paper accepted in the A&