Browsing by Author "Schmidt, GD"

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    Magnetic white dwarfs from the Sloan Digital Sky Survey: The first data release
    (2003) Schmidt, GD; Harris, HC; Liebert, J; Eisenstein, DJ; Anderson, SF; Brinkmann, J; Hall, PB; Harvanek, M; Hawley, S; Kleinman, SJ; Knapp, GR; Krzesinski, J; Lamb, DQ; Long, D; Munn, JA; Neilsen, EH; Newman, PR; Nitta, A; Schlegel, DJ; Schneider, DP; Silvestri, NM; Smith, JA; Snedden, SA; Szkody, P; Berk, DV
    Beyond its goals related to the extragalactic universe, the Sloan Digital Sky Survey (SDSS) is an effective tool for identifying stellar objects with unusual spectral energy distributions. Here we report on the 53 new magnetic white dwarfs discovered during the first two years of the survey, including 38 whose data are made public in the 1500 deg(2) First Data Release. Discoveries span the magnitude range 16.3 less than or equal to g less than or equal to 20.5, and based on the recovery rate for previously known magnetic white dwarfs, the completeness of the SDSS appears to be high for reasonably hot stars with B greater than or similar to 3 MG and g greater than or similar to 15. The new objects nearly double the total number of known magnetic white dwarfs and include examples with polar field strengths B-p > 500 MG, as well as several with exotic atmospheric compositions. The improved sample statistics and uniformity indicate that the distribution of magnetic white dwarfs has a broad peak in the range similar to5-30 MG and a tail extending to nearly 10(9) G. Degenerates with polar fields B-p greater than or similar to 50 MG are consistent with being descendents of magnetic Ap/Bp main-sequence stars, but low- and moderate-field magnetic white dwarfs appear to imply another origin. Yet-undetected magnetic F-type stars with convective envelopes that destroy the ordered underlying field are attractive candidates.
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    SDSS white dwarfs with spectra showing atomic oxygen and/or carbon lines
    (2003) Liebert, J; Harris, HC; Dahn, CC; Schmidt, GD; Kleinman, SJ; Nitta, A; Krzesinski, J; Eisenstein, D; Smith, JA; Szkody, P; Hawley, S; Anderson, SF; Brinkmann, J; Collinge, MJ; Fan, XH; Hall, PB; Knapp, GR; Lamb, DQ; Margon, B; Schneider, DP; Silvestri, N
    We discuss 18 white dwarfs, one of which (G227-5) was previously known, whose SDSS spectra show lines of neutral and/or singly ionized carbon. At least two and perhaps four show lines of neutral or singly ionized oxygen. Apart from the extremely hot "PG 1159'' stars, these are the first white dwarfs with photospheric oxygen detected in their optical spectra. The photometry strongly suggests that these stars lie in the 11,000-30,000 K temperature range of the helium-atmosphere DB white dwarfs, though only one of them shows weak neutral helium lines in the spectrum. Trigonometric parallaxes are known for G227-5 and another, previously known white dwarf (G35-26) showing atomic carbon lines, and they indicate that both are massive stars. Theoretical arguments suggest that all members of this class of rare white dwarfs are massive (similar to1 M.), and this finding could explain the paucity of massive DB white dwarfs.