Astronomy and Astrophysics, volume 307, 860-868 (1996/3-3)
High resolution UV spectroscopy of two hot (pre-) white dwarfs with the Hubble Space Telescope. KPD0005+5106 and RXJ2117+3412.
WERNER K., DREIZLER S., HEBER U., RAUCH T., FLEMING T.A., SION E.M. and VAUCLAIR G.
Abstract (from CDS):
High resolution UV spectra of KPD0005+5106 and RX J2117+3412 have been obtained with the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope. The data were subject to a non-LTE model atmosphere analysis. For KPD0005+5106, the hottest known helium-rich white dwarf, the C and N abundances as well as an upper limit for O have been determined (log(C/He)=-3, log(N/He)=-6, log(O/He)←5.5, by number), improving results from previous studies. These abundances are severely at odds with diffusion/radiative forces theory. They are possible primordial relics of their ancestral progenitor in the post-AGB phase. Besides the photospheric lines with a velocity shift of +35km/s we find a distinct interstellar/circumstellar absorption line system shifted by -15km/s. Difficulties are encountered with line profile fits to the spectrum of RX J2117+3412, an extremely hot hydrogen-deficient (PG1159-type) central star. Some of the strong C IV and O VI lines are too narrow to match the observations. Either the neglect of wind-effects in our models or the lack of reliable line broadening data may be responsible for this. A weak O V 1371A line is detected which suggests, that the effective temperature is higher than thought before (Teff=170000K). This means that RX J2117+3412 is the hottest known PG1159 star together with H1504+65. Interstellar and photospheric line spectra are clearly separated, with shifts of -19 and +23km/s, respectively. Both stars exhibit a strong O VIII emission line near 2977A, which cannot be of photospheric origin but probably arises from shock fronts along a stellar wind. The line widths are of the order of 150km/s. In addition, KPD0005+5106 shows another, equally strong emission feature near 2982A which either stems from photospheric N V or from non-photospheric C V.
stars: abundances - stars: evolution - stars: individual: RX J2117+3412 (RX J2117.1+3412) - stars: individual: KPD 0005+5106 - white dwarfs - ultraviolet: stars
RX J2117+3412 = RX J2117.1+3412
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