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Fast Hα Variations on a Rapidly Rotating Spotted Star

  • R. D. Robinson (a1) and A. Collier Cameron (a2)

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The star AB Dor (HD 36705) was first identified as an interesting object because of its strong Call H and K emission features (Bidelman and MacConnell 1973; Houk and Cowley 1975). It has a spectral class of G8 and appears to be a single star, since no radial velocity variations have thus far been detected, despite numerous attempts (e.g. Collier 1982; Innis et al. 1985a). Probably the most unusual and important feature about the star is its rapid rotational velocity, with a Vsini of 80 km s-1 (Collier 1982), which is more than 20 times that of a normal star of similar spectral class. AB Dor also shows a substantial photometric wave, commonly interpreted as indicating the presence of starspots. This wave has a typical amplitude of 0.05 to 0.15 magnitudes in V and a period of 0.514 days (e.g. Innis et al. 1985b). Combining this with the Vsini value gives a lower limit of 0.76 R for the stellar radius, while assuming the radius of a normal G8 dwarf yields an axial inclination of 60° ± 10°.

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References

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Bidelman, W. P. and MacConnell, D. J., 1973, Astron. J., 78, 687.
Collier, A. C., 1982, Mon. Not. R. Astron. Soc., 200, 489.
Collier Cameron, A., Bedford, D. K., Lloyd Evans, T., Rucinski, S. M., Vilhu, O. and White, N. E., 1986, in 4th Cambridge workshop on cool stars, stellar systems and the Sun, ed. Zeilik, M., in press.
Houk, N. and Cowley, A. P., 1975, Michigan Catalogue of 2 dimensional spectral types for the HD stars, Univ. Michigan, Ann Arbor, Vol. 1.
Innis, J. L., Nelson, G. J., Coates, D. W. and Thompson, K., 1985a, Inf. Bull. Var. Stars, 2667.
Innis, J. L., Robinson, R. D., Coates, D. W., and Thompson, K., 1985b, Proc. Astron. Soc. Aust., 6, 156.
Innis, J. L., Thompson, K., Coates, D. W., 1986, preprint.
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Rucinski, S. M., 1982, Inf. Bull. Var Stars, 2203.
Slee, O. B., Nelson, G. J., Innis, J. L., Stewart, R. T., Vaughan, A. and Wright, A. E., 1986, Proc. Astron. Soc. Ausi., 6, 312.
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Vogt, S. S. and Penrod, G. D., 1983b, Astrophys. J., 275, 661.

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