CAOSP abstracts, Volume: 27, No.: 3, year: 1998
- Author(s): STEPIEN, K.
- Journal: Contributions of the Astronomical Observatory Skalnate Pleso,
vol. 27, no. 3, p. 205-212.
- Date: 04/1998
- Title: Why are magnetic Ap stars slowly rotating?
- Keyword(s): STARS: ROTATION, STARS: CHEMICALLY PECULIAR, STARS: EARLY TYPE
- Pages: 205 -- 212
Observational data on rotation of Ap stars suggest that the bulk of
their rotation rates orm a separate Maxwellian distribution with
an average value 3-4 times lower than the normal star distribution.
No evidences for a significant angular momentum (AM) loss on the main
sequence (MS) have been found. It is thus concluded that Ap stars must
lose a large fraction of their initial angular momentum (AM) in the
pre-MS phase of evolution, most probably as a result of the interaction
of their primordial magnetic fields with accretion disks and stellar
winds. The observationally most acceptable values of accretion rate
from the disk, 10^(-8) M_(Sun)/year, of mass loss rate via a magnetized wind,
10^(-8) M_(Sun)/year, and of the surface magnetic field, 1 kG on the ZAMS,
result in the AM loss in full agreement with observations. There exists
a separate group of extremely slowly rotating Ap stars, with periods of the
order of 10-100 years. They are too numerous to come from the distribution
describing the bulk of Ap stars. It is conjectured that their extremely low
rotation rates are the result of additional AM loss on the MS.
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