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HST Spectroscopy of PG 1159 Stars: the Boundary of the GW VIR Instability Strip

Dreizler, S.

Our recent analysis of PG 1159 stars, mainly based on the HST spectroscopy, is presented. The results allow several conclusions regarding the boundary of the GW Vir instability strip and the driving mechanism for these pulsations.

HST Observation of GD 358

Kepler, S. O.; Winget, D. E.; Koester, D. +5 more

The success of asteroseismology lies in the correct identification of the star's normal modes of oscillation. Winget et al. (1994) identified the normal modes of a helium white dwarf pulsator, GD 358, through the frequency distribution of the pulsation. Robinson et al. (1995) described a new mode identification method by comparing the pulsation am…

Hst/uv Periodic Variations in the Intermediate Polar FO AQR

Mukai, K.; de Martino, D.; Buckley, D. A. H. +3 more

A preliminary analysis of high temporal HST UV spectroscopy, as well as SAAO BVRI photometry, has revealed that FO Aqr, differently from all previous observations, has changed from a spin dominated to an orbital dominated variability, both in lines and continuum. The spectral dependence of the orbital continuum, however, has not changed with time.…

HST Observations of Carbon and Hydrogen in DB White Dwarfs

Provencal, J. L.; Shipman, H. L.

The differences in the structure of DA and DB white dwarfs hinge on the asteroseismological analysis of GD 358. However, spectroscopic investigation of this important white dwarf found spectral peculiarities, notably a very low hydrogen abundance and the presence of carbon. These results initiated further investigation of chemical composition of D…