Disks of Be Stars & Their Pulsations &. Qingkang Li Department of Astronomy Beijing Normal University The Third Workshop of SONG, April, 2010. Collaborators: J. C. Brown, Dept. of Physics and Astronomy, University of Glasgow, UK
Department of Astronomy
Beijing Normal University
The Third Workshop of SONG, April, 2010
Superbubble in the
Large Magellanic CloudWind-Blown Bubbles in ISM
Pulsating starsin the HR diagram
βCep variables: pulsation periods P~2-10 hrs, low-order p and g modes, B0-B2
Slowly pulsating B (SPB) stars: P∽10-50 hrs, high-order g modes, B3-B9
Pulsating Be stars: P~similar to SPB up to 100-200 hrs
Be stars are non-supergiant B-type stars whose spectra have, or had at some time, one or more Balmer lines in emission. The mystery of the "Be phenomenon" is that the emission, which is well understood to originate from a flattened circumstellar disk (e.g. Struve, 1931), can come and go episodically on time scales of days to decades.
H low-order p and g modes, B0-B2b
How do Be stars
1. What source of energy elevates matter to orbits well above the stellar surface?
2. How does the matter obtain the angular momentum and orbit around the star with Keplerian speed with no observed outflow?
3. How are the very high observed disk density attained?
(1) Wind compressed disk model
(Bjorkman, Cassinelli, 1993, ApJ, 409, 429)
(2) Episodic mass ejection model follows:
(Ando, 1986, A&A, 163, 97; Owocki & Cranmer, 2002, ASP 259, 512, 951; Cranmer, 2009, ApJ, 701, 396)
Observations confirm that Be star line-profile variability is due to the non-radial pulsations (NRP). Some mixed modes of NRP (retrograde) are associated with the transport of angular momentum up to the surface and beyond, saying, pulsational energy may leak out of a hot star into circumstellar medium.
(Cassinelli, et al., 2002, ApJ, 578, 951)
(Brown, et al., 2004, MNRAS, 352, 1061)
Painted by John C. Brown follows: