Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21542824d&link_type=abstract
American Astronomical Society, AAS Meeting #215, #428.24; Bulletin of the American Astronomical Society, Vol. 42, p.348
Astronomy and Astrophysics
Astrophysics
Scientific paper
Classical "Be” stars are massive, rapidly rotating stars having gaseous circumstellar decretion disks which are known to sometimes dissipate and regenerate. Since the mechanism for forming these disks is not known, observing these stars when they transition between a "Be” phase and a normal B star phase can help constrain what causes the disks to form. We have analyzed 15 years of spectroscopic and spectropolarimetric data from the Ritter and Pine Bluff Observatories of two "Be” stars, 60 Cygni and Pi Aquarii, during which such a transition phase from Be to B star occurred. The time-scale of 60 Cyg's disk loss was 1000 days, during which the disk emission declined monotonically, while Pi Aqr's disk loss episode lasted 2440 days and was interrupted by two major injection events of new disk material. We used the wavelength dependence of polarization during each stars disk-less phase to determine the interstellar polarization. Analysis of the intrinsic polarization and H-alpha equivalent width measurements show that both disks faded in an inside-out manner, with timescales much longer than the orbital periods of their binary companions. We also detect small deviations away from the overall disk position angle in our polarization data; we speculate that this might be indicative of either a warp in the inner disk region or the injection of new disk material at an inclined orbit to the plane of the pre-existing disk. We also present our initial efforts to model time dependent behavior of our spectropolarimetric data using 3D Monte Carlo Radiative transfer codes.
JPW acknowledges support from NSF Astronomy & Astrophysics Postdoctoral Fellowship AST 08-02230, and ZHD acknowledges support from the UW Pre-MAP program. HPOL observations were supported under NASA contract NAS5-26777 with University of Wisconsin-Madison. Observations at Ritter Observatory have been supported by the NSF under PREST grant AST 04-40784.
Bjorkman Jon E.
Bjorkman Karen S.
Draper Zachary H.
Kowalski Adam F.
Meade Marilyn R.
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