Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.3705c&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #37.05; Bulletin of the American Astronomical Society, Vol. 24, p.787
Astronomy and Astrophysics
Astronomy
Scientific paper
In this paper we discuss the possible existence of zonal wind-belts in the atmospheres of rapidly rotating early type stars analogous to the type found in planetary atmospheres. Unlike previous investigations into differential rotation, the velocity field yielded by these wind belts is assumed to be an atmospheric phenomenon and therefore does not significantly alter the shape or flux distribution resulting from gravity darkening. However, the modification to the surface gravity and velocity field brought about by the presence of such winds can be expected to affect the shapes of rotationally broadened lines. While the changes in the line profiles are generally small, they significantly complicate the interpretation of small departures of such profiles from classical rotationally broadened line profiles. Our estimates of the velocity stem from the assumption of a relation between the magnitude and latitudinal wavenumber of the zonal velocity field, in addition to the assumption that the flow is close to being ``geostrophic,'' i.e. where the pressure gradient nearly balances the local coriolis forces. From this basis, we construct a series of barotropic atmosphere models for the surface velocity field. Following earlier efforts we then construct line profiles for Mg II (4481), He I (4471), and the first three Balmer lines appropriate for these models. We compare integrated line profiles for these models exhibiting varying numbers of zonal belts with the line profiles of uniformly rotating models. Various characteristics of the line profiles such as half widths (FWHM) and equivalent widths are given. Qualitative changes in the shapes of the profiles can be related to the direction of the zonal winds with respect to the underlying angular motion of the model. We also obtain theoretical atmospheric quantities such as Johnson and Stromgren photometric indices, absolute magnitudes, and net polarization information, and make comparisons with the uniformly rotating models.
Collins George W. II
Cranmer Steven R.
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