The circumstellar environment of Rigel probed at high spatial and spectral resolution
Andreas Kaufer, European Southern Observatory, Santiago, Chile
Olivier Chesneau, A.Spang, C.Colvinter, Observatoire de la Cote d'Azur, Nice, France
Otmar Stahl, ZAH, Landessternwarte, Heidelberg, Germany
Luc Dessart, Laboratoire d'Astrophysique de Marseille, Marseille, France
Raman Prinja, University College London, London, United Kingdom
Rolf Chini, UCN, Antofagasta, Chile

The presence of highly structured circumstellar environments in late B- and early A-type supergiants is well established 
through extensive spectroscopic, photometric, and polarimetric time series observations. The circumstellar structures are 
located within a few stellar radii in the transition zone from the stellar photosphere to the inner wind region of the expanding 
envelopes of the stars. 
The physical mechanisms that generate the observed circumstellar structures remain subject of debate. Coupling of stellar 
surface structures into the inner wind regions combined with rotational modulation is generally favoured with the surface 
structure being results of multi-mode non-radial pulsation patterns or complex magnetic fields structures. However, little 
observational evidence is available to narrow down the underlying mechanisms.
Optical and near-IR interferometry at high spectral resolution has high potential to shed new light on the circumstellar 
environments of massive supergiants. We present results from spectro-interferometric studies of the prototypical late B 
supergiant Rigel (beta Orionis, B8Ia). Rigel has for the first time been monitored over several rotational cycles with the 
AMBER 3-beam combiner instrument at the VLTI in 2006/7 and 2009/10. The observations targeted the photosphere- and 
wind-sensitive Br Gamma line at a resolving power of R=12000. The analysis of the measured interferometric visibilies 
provides constraints on the extension of the line-forming region in photosphere and wind; the observed variabilty of the 
differential phases across the line profile gives indications on the dynamics and the geometry of the circumstellar structures of 
Rigel.