Variable rotational line broadening in the Be star Achernar
Th. Rivinius1, D. Baade2, R.H.D. Townsend3, A. C. Carciofi4, S. Štefl51 ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile
2 ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Garching, Germany, Karl-Schwarzschildstr. 2
3Department of Astronomy, Univ.\ of Wisconsin-Madison, 2535 Sterling Hall, 475 N. Charter Street, Madison, WI 53706, USA4 Instituto de Astronomia, Geofísica e Ciéncias Atmosféricas, Universidade de São Paulo, Brazil
5 ESO/ALMA, Alonso de Córdova 3107, Vitacura, Santiago, Chile
The main theoretical problem for the formation of a Keplerian disk around Be stars is how to supply angular momentum from the star to the disk, even more so since Be stars probably rotate somewhat sub-critically. For instance, nonradial pulsation may transport angular momentum to the stellar surface until (part of) this excess supports the disk formation/replenishment. The nearby Be star Achernar is presently building a new disk and offers an excellent opportunity to observe this process from relatively close-up. Spectra from various sources and epochs are scrutinized to identify the salient stellar parameters characterizing the disk life cycle as defined by H-alpha emission. Variable strength of the non-radial pulsation is confirmed, but does not affect the further results. For the first time it is demonstrated that the photospheric line width does vary in a Be star, by as much as Delta v sin i less than 35km/s. However, contrary to assumptions in which a photospheric spin-up accumulates during the diskless phase and then is released into the disk as it is fed, the apparent photospheric spin-up is positively correlated with the appearance of H-alpha line emission: The photospheric line widths and circumstellar emission increase together, and the apparent stellar rotation declines to the value at quiescence after the H-alpha line emission becomes undetectable.
Accepted by Astronomy&Astrophysics as Letter
or on the web at: arXiv:1309.7286