HD 33798 is a chromospherically active, rapidly rotating, lithium-rich, late-type giant. Analysis of 40 radial velocities indicates no periodic velocity variations, suggesting that the star is single, so its rapid rotation (v sin i = 29 km s-1) is highly unusual. Such rotation is inconsistent with the rotational brake hypothesis of Gray [ApJ, 262, 682 (1982); 347, 1021 (1989)] and the results of Rutten & Pylyser [A&A, 191, 227 (1988)]. Although there are many similarities to the supposed pre-main-sequence star HDE 283572, the lithium abundance and space motion of HD 33798 appears to be in a post-main-sequence phase of evolution, but its previous evolutionary history is uncertain. Its space motion is similar to FK Com, suggesting that it is a coalesced binary in the process of spinning down. However, if that is so, its large lithium abundance needs to be explained. A scenario in which the star was a rapidly rotating late B or early A star that has recently crossed the H-R gap and become a convective late-type giant could explain the large lithium abundance but is inconsistent with the space velocity components. A third scenario in which material is transferred from a rapidly rotating core may be the most likely.
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Fekel, Francis C. and Laurence A. Marschall. Chromospherically Active Stars IX HD 33798 = V390 Aurigae: A Lithium-Rich Rapidly Rotating Single Giant. The Astronomical Journal (October 1991) 102(4):1439-1445.
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