FK Comae--The Kinematical Determination of its Age and Evolutionary Status.

The variable star FK Com is a rapidly rotating G giant (P rot = 2.40 days) with strong Hα and Cα II H + K line emissions. The large angular momentum of FK Com cannot be explained through the evolution of a single star, but high-precision radial-velocity studies so far have failed to show it to be a close binary system. Therefore, it has been proposed by Bopp and Rucinski (1981) that FK Com is a single star that coalesced from a close binary according to the evolutionary scheme of Webbink (1976). On the other hand, Walter and Basri (1982) have proposed that FK Com is a terminally evolving Algol-type binary with a secondary component of such low mass that it has not been detected. in the present study we have estimated the age of the star from its UVW space motions. The space-velocity components (U = + 46 km/s, V = - 67 km/s, W = - 11 km/s) and resultant space motion of S = 82 km/s (relative to the Sun) were determined from the star's proper motion, radial velocity, and assumed distance of 250 pc. From its space motion and distance above the Galactic plane (z = 245 ± 50 pc), FK Com appears to be a member of the old disk population stars with an inferred age between ≍ 5-10 &*times; l0^9 yr. The age inferred for FK Com lends support to the hypothesis that it evolved from the recent coalescence of a close binary in which the original mass of the primary component was ≍1 - 1.5 M sun.

Main Author: Guinan, Edward F.
Other Authors: Robinson, Craig R.
Language: English
Published: 1985
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