Far-Ultraviolet Spectroscopy of PG 1159 Stars with the Hopkins Ultraviolet Telescope

Details Far-Ultraviolet Spectroscopy of PG 1159 Stars with the Hopkins Ultraviolet Telescope Far-Ultraviolet Spectroscopy of PG 1159 Stars with the Hopkins Ultraviolet Telescope

Aug 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...502..858k&link_type=abstract

Astrophysical Journal v.502, p.858

Astronomy and Astrophysics

Astronomy

27

Line Identifications, Stars: Abundances, Stars: Agb And Post-Agb, Ultraviolet: Stars, Stars: White Dwarfs

Scientific paper

We present for the first time systematic far-ultraviolet (FUV) spectroscopy that extends down to the hydrogen Lyman edge for five representative PG 1159 stars (H1504+65, K1-16, PG 1424+535, PG 1707+427, and PG 1159-035). In addition, we have observed the hottest known DO white dwarf (KPD 0005+5106) and the hot hydrogen-rich central star of the planetary nebula Sh 2-216. The medium-resolution spectra were taken with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission in 1995. We have performed line identifications and non-LTE model atmosphere fits. The results confirm earlier analyses of optical and UV data and complement recent Hubble Space Telescope Goddard High-Resolution Spectrograph UV spectroscopy. The following conclusions are drawn from the HUT data. The absence of absorption lines from the He II Balmer series finally proves the helium deficiency in H1504+65 and confirms its nature as a naked C/O stellar core. The detection of a P Cygni profile from the O VI resonance line in the spectrum of the central star of K1-16 allows a first reliable determination of the mass-loss rate from a PG 1159 star. It suggests that the wind is radiation driven. The spectra of the pulsator/nonpulsator pair PG 1707+427 and PG 1424+535 reveal differences, which could not be detected with optical spectroscopy, in the photospheric parameters. In particular, we announce the detection in the pulsator PG 1707+427 of nitrogen, which is a remarkable phenomenon among PG 1159 stars. Also, in the prototype itself we find hints for photospheric nitrogen. The hot DO KPD 0005+5106 exhibits H2 absorption lines similar to those found in the spectrum of the central star Sh 2-216. This may signify the presence of an old planetary nebula surrounding the DO star.

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