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Astron. Astrophys. 347, 550-555 (1999)
1. Introduction
HD 112989 = 37 Com, is a fifth-magnitude single giant star, with a spectral type G9III to G9III-II. Tomkin et al. (1976) have found an unusually low 12C/13C ratio of about 3.4, significantly lower than the solar value, indicating clearly that the composition of the atmosphere of this star was altered by material processed by the CNO cycle in its interior and subsequently dredged-up to the surface by an extensive convective envelope. Such finding shows that HD 112989 seems to be very probably a fairly evolved and well-mixed star. Brown et al. (1989) reported a normal content of Lithium for this star, in agreement with the standard predictions.
On the basis of a large set of differential UBV photometric observations Strassmeier & Hall (1988a) have found light variations which could presumably be due to spots on its surface, but have found no evidence of periodicity. The star's behavior in the Strömgren by filters was investigated by Lockwood et al. (1997) on a 10 year interval. They reported changes in the short-term variability rate and the presence of a long-term variability.
According to Maggio et al. (1990) HD 112989 is a normal X-ray emitter, presenting the same characteristic behavior of ordinary late G and early K giant stars. The ROSAT all-sky survey (Hunsch et al., 1998) also found that the star is a moderate X-ray emitter compared with the other single G and K giants from the catalogue. Reimers et al. (1996) have reported the absence of CS CaII H&K lines in the spectrum of such star.
In this work we present new spectroscopic and photometric observations for this unusual giant star, as well as a discussion on its evolutionary status.
© European Southern Observatory (ESO) 1999
Online publication: June 30, 1999
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