Spectral analysis of the sdO K 648, the exciting star of the planetary nebula Ps 1 in the globular cluster M 15 (NGC 7078)*
Institut für Astronomie und Astrophysik, Universität Tübingen, 72076 Tübingen, Germany
2 Dr. Remeis-Sternwarte, Universität Erlangen-Nürnberg, 96049 Bamberg, Germany
Corresponding author: T. Rauch, firstname.lastname@example.org
Accepted: 29 October 2001
We present a spectral analysis of the sdO central star K 648 based on medium-resolution optical and high-resolution UV spectra. The photospheric parameters are determined by means of state-of-the-art NLTE model atmosphere techniques. We found and . The helium () and oxygen () abundances are about solar while carbon is enriched by a factor of 2.5 (). Nitrogen (, ) appears at a sub-solar value. However, these metal abundances are much higher than the cluster's metallicity (M 15: ). The surface composition appears to be a mixture of the original hydrogen-rich material and products of helium burning ( process) which have been mixed up to the surface. The abundances of He, C, and N are consistent with the nebular abundance, while O is considerably more abundant in the photosphere than in the nebula. From a comparison of its position in the – plane with evolutionary calculations a mass of and a luminosity of are deduced. Our spectroscopic distance is in agreement with the distance of M 15 as determined by Alves et al. (2000). From the GHRS spectra we measure a radial velocity of .
Key words: Galaxy: globular clusters: individual: M 15 / ISM: planetary nebulae: individual: Ps 1 / stars: abundances / stars: AGB and post-AGB / stars: evolution / stars: individual: K 648
Based on observations obtained at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy, on data retrieved from the International Ultraviolet Explorer (IUE) Final Archive, on observations made with the Hubble Space Telescope (HST, GO Proposal ID: 3513, PI: Heber), and on HST data retrieved from the ST-ECF archive.
© ESO, 2002