Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993adspr..13...12w&link_type=abstract
Advances in Space Research (ISSN 0273-1177), vol. 13, no. 12, p.(12)399-(12)402
Astronomy and Astrophysics
Astronomy
9
Carbon, Helium, Hydrogen, Light (Visible Radiation), Oxygen, Planetary Nebulae, Stellar Atmospheres, Stellar Models, Stellar Spectra, White Dwarf Stars, X Ray Astronomy, Proportional Counters, Rosat Mission, Sky Surveys (Astronomy), Thermodynamic Equilibrium, X Ray Telescopes
Scientific paper
We summarize the analysis of a new PG 1159 star, i.e., a hydrogen deficient pre-white dwarf detected in the ROSAT X-Ray Telescope all sky survey. The X-ray source RX J2117.1+3412 is relatively faint (approximately 0.33 cnt/s) and was selected for optical identification on the basis of its extreme X-ray softness. With V=13.2, the counterpart of the X-ray source is in the optical; the second brightest member of the PG 1159 class. CCD imagery reveals that the star is surrounded by an old highly excited planetary nebula of faint surface brightness. Optical line profiles of He II, C IV, and O VI and the overall optical and ROSAT Position-Sensitive Proportional Counter (PSPC) (0.1-2.4 keV) energy distributions are compared to predictions of non-local thermodynamic equilibrium (NLTE) model atmospheres. We find an excellent agreement between the atmospheric parameters derived from optical and soft X-ray data. The effective temperature of the star is extremely high (150,000 K). Abundances of He, C and O are found to be consistent with those derived in other PG 1159 stars, whereas the surface gravity is significantly smaller in RX J2117.1+3412. New optical spectra presented here show the presence of ultra-high excitation lines of O VIII.
Motch Ch.
Pakull Manfred W.
Werner Kirstin
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