Does Rotation Alone Determine Whether an A-Type Star's Spectrum Is Abnormal or Normal?

Details Does Rotation Alone Determine Whether an A-Type Star's Spectrum Is Abnormal or Normal? Does Rotation Alone Determine Whether an A-Type Star's Spectrum Is Abnormal or Normal?

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...544..933a&link_type=abstract

The Astrophysical Journal, Volume 544, Issue 2, pp. 933-936.

Astronomy and Astrophysics

Astronomy

26

Stars: Binaries: Spectroscopic, Diffusion, Stars: Peculiar, Stars: Rotation

Scientific paper

As noted by Abt & Morrell, virtually all of the metallic line (Am) and peculiar A (Ap) stars have equatorial rotational velocities less than 120 km s-1, and most of the normal A0-F0 main-sequence stars have equatorial rotational velocities greater than 120 km s-1. However, at all spectral types there are some (10%-20%) of the normal stars that have smaller rotational velocities. If this overlap is real, then a star's rotational velocity is insufficient to explain its abnormal or normal spectra. We studied the A5-F0 and A2-A4 stars and found in both cases that there are stars classified as ``normal'' that have unusually weak Ca II K lines and/or that occur in short-period binaries. Therefore, the overlap seems to be due to undetected marginal abnormal stars. Among the A0-A1 stars we find that our inability to distinguish consistently the class IV from the class V stars can explain the overlap because the class IV stars have lower rotational velocities than class V stars. We conclude from statistical arguments that rotation alone can explain the appearance of an A star as either abnormal or normal.

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