Institut für Astronomie und Astrophysik Abteilung Astronomie Sand 1, D-72076 Tübingen, Germany
Hinweis: Einige Seiten auf astro.uni-tuebingen.de können veraltet sein und werden nicht mehr aktualisiert. Note: Some webpages at astro.uni-tuebingen.de may be outdated and will no longer be updated.

Preprint 04/01

Spectral analysis of the sdO K648, the exciting star of the planetary nebula Ps1 in the globular cluster M15 (NGC 7078}

T. Rauch (1), U. Heber (2), and K. Werner (1)

(1) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
(2) Dr. Remeis-Sternwarte, Universität Erlangen-Nürnberg, D-96049 Bamberg, Germany

To appear in: Astronomy & Astrophysics

Abstract.

We present a spectral analysis of the sdO central star K648 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 T_eff=39+/-2 kK and log g=3.9+/-0.2. The helium (n_He/n_H=0.08) and oxygen (n_O/n_H=0.001) abundances are about solar while carbon is enriched by a factor of 2.5 (n_C/n_H=0.001). Nitrogen (n_N/n_H=1*10^-6, [N/H]=-2.0) appears at a sub-solar value. However, these metal abundances are much higher than the cluster's metallicity (M15: [Fe/H]=-2.25).The surface composition appears to be a mixture of the original hydrogen-rich material and products of helium burning (3-alpha 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 logT_eff - logg plane with evolutionary calculations a mass of 0.57^+0.02_-0.01 M_sol and a luminosity of 3810+/-1200 L_sol are deduced. Our spectroscopic distance d=11.1^+2.4_-2.9 kpc is in agreement with the distance of M15 as determined by Alves et al. (2000). From the GHRS spectra we measure a radial velocity of v_rad = -130 km/sec.

Key words: Galaxy: globular clusters: individual: M15 - ISM: planetary nebulae: individual: Ps1 - Stars: abundances - Stars: AGB and post-AGB - Stars: evolution - Stars: individual: K648}

Paper (340k gzip'ed Postscript including figures)

[Home Page] [Preprints 2001] [Quick Reference] [Feedback]

| Impressum Last modified 14 Nov 2002