NLTE-analysis of the sdO star ROB 162 in the globular cluster NGC 6397.
Abstract
A high-resolution visual blue spectrum of the subluminous O star ROB 162 in the globular cluster NGC 6397 has been analysed for its atmospheric parameters by means of NLTE model atmospheres. The effective temperature Teff = 51000±2000K, the gravity log g = 4.5±0.2 and a normal helium mass fraction (Y = 0.28 (+0.04, -0.06)) resulted. Spectroscopically, ROB 162 appears not to be a population II counterpart of the field sdO stars. Instead, it resembles a (metal-poor) central star of a planetary nebula (CPN) although no nebula has been found so far. From comparison with evolutionary calculations it is concluded that ROB 162, like the CPNs, is a post-AGB star of 0.55 M_sun; - 0.6 M_sun;. It is conjectured that a hypothetical nebula is already dispersed or too faint to be detected.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 1986
- Bibcode:
- 1986A&A...169..244H
- Keywords:
-
- Globular Clusters;
- Nonequilibrium Thermodynamics;
- O Stars;
- Planetary Nebulae;
- Stellar Models;
- Abundance;
- Asymptotic Giant Branch Stars;
- Atmospheric Models;
- Stellar Evolution;
- Stellar Luminosity;
- Ultraviolet Spectra;
- White Dwarf Stars;
- Astrophysics