StHfi-55: A CARBON MIRA, NOT A SYMBIOTIC BINARY

We carried out a V RCIC photometric monitoring of StHfi 55. In addition, we obtained low resolution absolute spectro-photometry and high resolution Echelle spectroscopy of the star. Our data show that StHfi 55 is a carbon Mira, pulsating with a 395 day period, with = 13.1 mean brightness and ¢V = 2.8 mag amplitude. It has a low reddening of EBiV = 0.15, lies at a distance of 5 kpc from the Sun and 1 kpc from the Galactic plane, and its heliocentric systemic velocity is close to +22 km s i1 . The difierence between the radial velocity of the optical absorption spectrum and that of the Hfi emission is unusually small for a carbon Mira. The spectrum of StHfi 55 can be classifled as C-N5 C26 i . Its 13 C/ 12 C isotopic ratio is normal, and the lines of BaII and other s-type elements, as well as LiI, have the same intensity as in fleld carbon stars of similar spectral type. The Balmer emission lines are very sharp and unlike those seen in symbiotic binaries. Their intensity changes in phase with the pulsation cycles in the same way as seen in fleld carbon Miras. We therefore conclude that StHfi 55 is a bona flde, normal carbon Mira showing no feature supporting a symbiotic binary classiflcation, which has been suggested previously.