Publication Date:
2019-07-13
Description:
About a dozen hot white dwarfs with effective temperatures T(sub eff) = 65000120000 K exhibit unusual absorption features in their optical spectra. These objects were tentatively identified as Rydberg lines of ultra-high excited metals in ionization stages vx, indicating line formation in a dense environment with temperatures near 106 K. Since some features show blueward extensions, it was argued that they stem from a superionized wind. A unique assignment of the lines to particular elements is not possible, although they probably stem from C, N, O, and Ne. To further investigate this phenomenon, we analyzed the ultraviolet spectra available from only three stars of this group; that is, two helium-rich white dwarfs, HE 05042408 and HS 0713+3958 with spectral type DO, and a hydrogen-rich white dwarf, HS 2115+1148 with spectral type DAO. We identified light metals (C, N, O, Si, P, and S) with generally subsolar abundances and heavy elements from the iron group (Cr, Mn, Fe, Co, Ni) with solar or oversolar abundance. The abundance patterns are not unusual for hot WDs and can be interpreted as the result of gravitational settling and radiative levitation of elements. As to the origin of the ultra-high ionized metals lines, we discuss the possible presence of a multicomponent radiatively driven wind that is frictionally heated.
Keywords:
Astrophysics; Space Radiation
Type:
GSFC-E-DAA-TN66627
,
Astronomy and Astrophysics (ISSN 0004-6361) (e-ISSN 1432-0746); 609; A107
Format:
application/pdf
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