Non-lte model atmosphere analysis of the large magellanic cloud supersoft x-ray source CAL 83

Thierry Lanz, Gisela A. Telis, Marc Audard, Frits Paerels, Andrew P. Rasmussen, Ivan Hubeny

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

We present a non-LTE (NLTE) model atmosphere analysis of Chandra High Resolution Camera (HRC-S) and Low Energy Transmission Grating (LETG) and XMM-Newton Reflection Grating Spectrometer (RGS) spectroscopy of the prototypical supersoft source CAL 83 in the Large Magellanic Cloud. Taken with a 16 month interval, the Chandra and XMM-Newton spectra are very similar. They reveal a very rich absorption-line spectrum from the hot white dwarf photosphere but no spectral signatures of a wind. We also report a third X-ray off-state during a later Chandra observation, demonstrating the recurrent nature of CAL 83. Moreover, we found evidence of short-timescale variability in the soft X-ray spectrum. We completed the analysis of the LETG and RGS spectra of CAL 83 with new NLTE line-blanketed model atmospheres that explicitly include 74 ions of the 11 most abundant species. We successfully matched the Chandra and XMM-Newton spectra assuming a model composition with LMC metallicity. We derived the basic stellar parameters of the hot white dwarf, but the current state of atomic data in the soft X-ray domain precludes a detailed chemical analysis. We have obtained the first direct spectroscopic evidence that the white dwarf is massive (MWD ≳ M⊙). The short timescale of the X-ray off-states is consistent with a high white dwarf mass. Our analysis thus provides direct support for supersoft sources as likely progenitors of Type la supernovae (SNe Ia).

Original languageEnglish (US)
Pages (from-to)517-526
Number of pages10
JournalAstrophysical Journal
Volume619
Issue number1 I
DOIs
StatePublished - Jan 20 2005

Keywords

  • Binaries: close
  • Stars: atmospheres
  • Stars: fundamental parameters
  • White dwarfs
  • X-rays: binaries
  • X-rays: individual (CAL 83)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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