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Rotational Velocities for the Brighter A-Type Stars

Published online by Cambridge University Press:  12 April 2016

Helmut A. Abt  and
Nidia I. Morrell
Helmut A. Abt
Affiliation:
Kitt Peak National Observatory, Box 26732, Tucson, AZ 85726-6732, USA
Nidia I. Morrell
Affiliation:
Facultad de Ciencias Astronomica y Geofisicas, Universidad Nacional de La Plata, La Plata, Argentina

Abstract

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In 1968 van den Heuvel showed that the rotational velocities at many A types have peaks below V sin i = 45 km s−1 and above 90 km s−1. We explored this bimodal behavior by obtaining new rotational velocities of 1761 A-type stars with coudé CCD spectra and, to date, new MK classifications for 956 of those. We find that the slow rotators consist of Ap, Am, and short-period binaries while the rapid rotators are normal and λ Bootis stars. The overlap is only 8–10% and can probably be attributed to undetected abnormal stars and binaries.

The λ Bootis stars discovered purely by their having weak λ4481 Mg II constitute about 18% of the early A-type stars but 4% at the late ones. Statistically all such λ Bootis stars have V > 100 km s−1 but they constitute only a small fraction of those stars.

More than half of the stars classified as A2 IV (and some at Al IV and A3 IV) seem to be a hitherto unrecognized class of slowly-rotating abnormal-abundance stars of luminosities like those of class V stars.

Type
IV. Related Stars
Information
International Astronomical Union Colloquium , Volume 138: Peculiar versus Normal Phenomena in A-Type and Related Stars , 1993 , pp. 384 - 393
Copyright
Copyright © Astronomical Society of the Pacific 1993

References

Abt, H.A. 1984, in The MK Process and Stellar Classification, ed. Garrison, R.F. (Toronto: David Dunlap Obs.), 340 Google Scholar
Abt, H.A., & Moyd, K.I. 1973, ApJ, 182, 809 Google Scholar
Charbonneau, P. 1991, ApJ, 372, L33 CrossRefGoogle Scholar
Cowley, A., Cowley, C., Jaschek, M., & Jaschek, C. 1969, AJ, 74, 375 CrossRefGoogle Scholar
Gray, R.O., & Garrison, R.F. 1987, ApJS, 65, 581 Google Scholar
Gray, R.O., & Garrison, R.F. 1989, ApJS, 70, 623 Google Scholar
Henry, R.C., & Hesser, J.E. 1971, ApJS, 23, 421 Google Scholar
Hoffleit, D. 1964, Catalogue of Bright Stars (New Haven: Yale Univ. Obs.)Google Scholar
Michaud, G. 1970, ApJ, 160, 641 Google Scholar
Michaud, G., & Charland, Y. 1986, ApJ, 311, 326 CrossRefGoogle Scholar
Morgan, W.W., Abt, H.A., & Tapscott, J.W. 1978, Revised MK Spectral Atlas for Stars Earlier Than the Sun (Williams Bay: Yerkes Obs. and Tucson: Kitt Peak Nat. Obs.)Google Scholar
Slettebak, A. 1949, ApJ, 110, 498 Google Scholar
Slettebak, A., Collins, G.W. II, Boyce, P.B., White, N.M., & Parkinson, T.D. 1975, ApJS, 29, 137 Google Scholar
van den Heuvel, E.P.J. 1968, BAN, 19, 309 Google Scholar