On the nature of spectral features in peculiar DQ white dwarfs

Details On the nature of spectral features in peculiar DQ white dwarfs On the nature of spectral features in peculiar DQ white dwarfs

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..274s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 1, p. 274-280

Astronomy and Astrophysics

Astrophysics

39

Polarization, Spectrum Analysis, Swan Bands, White Dwarf Stars, Abundance, Astronomical Polarimetry, Astronomical Spectroscopy, Carbon Compounds, Frequency Shift, Helium, Hydrogen, Stellar Magnetic Fields, Visible Spectrum

Scientific paper

Spectropolarimetric measurements are presented for the DQ white dwarfs ESO 439-162, LHS 1126, and G225-68, whose spectroscopic features in the optical have been interpreted in the past as pressure-shifted or magnetically shifted C2 Swan bands. The results convincingly demonstrate that none of these objects is strongly magnetic, with upper limits of 30, 3, and 2 MG respectively. Since Bergeron et al. (B 94) have recently ruled out the pressure-shift interpretation for LHS 1126 as well, we discuss alternative physical mechanisms for displacing the Swan bands. Although possibilities for explaining the observed shifts may exist, a comparison of the optical spectra (and that of a similar DQ star, LP 77-57) indicates that the locations and shapes of the profiles in all four objects are virtually identical. This last result suggests instead that a different molecular species could be responsible. A detailed chemical equilibrium analysis of H/He/C mixtures under the physical conditions encountered in the atmospheres of these peculiar objects reveals that C2H is a molecule preferentially formed in the photospheric regions. The nature and evolution of these objects are discussed.

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