High-resolution extreme ultraviolet spectroscopy of G191-B2B: Structure of the stellar photosphere and the surrounding interstellar medium

M. A. Barstow, R. G. Cruddace, M. P. Kowalski, N. P. Bannister, D. Yentis, J. S. Lapington, J. A. Tandy, I. Hubeny, S. Schuh, S. Dreizler, T. W. Barbee

Research output: Contribution to journalArticle

14 Scopus citations

Abstract

We have continued our detailed analysis of the high-resolution (R = 4000) spectroscopic observation of the DA white dwarf G191-B2B, obtained by the Joint Astrophysical Plasma-dynamic Experiment (J-PEX) normal incidence sounding rocket-borne telescope, comparing the observed data with theoretical predictions for both homogeneous and stratified atmosphere structures. We find that the former models give the best agreement over the narrow waveband covered by J-PEX, in conflict with what is expected from previous studies of the lower resolution but broader wavelength coverage Extreme Ultraviolet Explorer spectra. We discuss the possible limitations of the atomic data and our understanding of the stellar atmospheres that might give rise to this inconsistency. In our earlier study, we obtained an unusually high ionization fraction for the ionized He II present along the line of sight to the star. In the present paper, we obtain a better fit when we assume, as suggested by Space Telescope Imaging Spectrograph results, that this Hen resides in two separate components. When one of these is assigned to the local interstellar cloud, the implied He ionization fraction is consistent with measurements along other lines of sight. However, the resolving power and signal-to-noise available from the instrument configuration used in this first successful J-PEX flight are not sufficient to clearly identify and prove the existence of the two components.

Original languageEnglish (US)
Pages (from-to)1273-1278
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Volume362
Issue number4
DOIs
StatePublished - Oct 1 2005

Keywords

  • ISM: general
  • Stars: atmospheres
  • Ultraviolet: stars
  • White dwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Barstow, M. A., Cruddace, R. G., Kowalski, M. P., Bannister, N. P., Yentis, D., Lapington, J. S., Tandy, J. A., Hubeny, I., Schuh, S., Dreizler, S., & Barbee, T. W. (2005). High-resolution extreme ultraviolet spectroscopy of G191-B2B: Structure of the stellar photosphere and the surrounding interstellar medium. Monthly Notices of the Royal Astronomical Society, 362(4), 1273-1278. https://doi.org/10.1111/j.1365-2966.2005.09394.x