Hot degenerates in the Montreal-Cambridge-Tololo survey. 2: Two new hybird white dwarfs, MCT 0128-3846 and MCT 0453-2933, and the nature of the DAB stars

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view Abstract Citations (25) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hot Degenerates in the Montreal-Cambridge-Tololo Survey. II. Two New Hybrid White Dwarfs, MCT 0128-3846 and MCT 0453-2933, and the Nature of the DAB Stars Wesemael, F. ; Bergeron, P. ; Lamontagne, R. L. ; Fontaine, G. ; Beauchamp, A. ; Demers, S. ; Irwin, M. J. ; Holberg, J. B. ; Kepler, S. O. ; Vennes, S. Abstract We report the discovery, in the course of a survey for high-latitude, ultraviolet-excess objects in the southern hemisphere, of two new hybrid DAB stars. Both objects exhibit a weak He I 4471 A line superposed onto the usual Balmer line spectrum. Analysis of the Balmer series with both homogeneous and stratified models show these stars to have spectroscopic effective temperatures around 27,000 K. However, low-dispersion ultraviolet observations with the IUE reveal energy distributions considerably flatter than those of normal DA stars near that effective temperature. These energy distributions are inconsistent as well as those of stratified models calculated at the temperature and hydrogen-layer mass determined from the optical spectrum. We demonstrate instead that consistent fits to the optical and ultraviolet spectrum, as well as to the energy distribution, can be achieved if these objects are unresolved, composite systems consisting of a DA white dwarf together with a DB or DBA star. The DAB spectral class thus appears inhomogeneous, and may contain both composit systems and stratified stars. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174326 Bibcode: 1994ApJ...429..369W Keywords: Balmer Series; Helium Atoms; Ultraviolet Astronomy; White Dwarf Stars; Atmospheric Composition; Iue; Purity; Spectral Energy Distribution; Stellar Models; Astrophysics; STARS: BINARIES: GENERAL; STARS: INDIVIDUAL ALPHANUMERIC: MCT 0128-3846; STARS: INDIVIDUAL ALPHANUMERIC: MCT 0453-2933; STARS: WHITE DWARFS; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (7) MAST (1) INES (1) Related Materials (1) Part 1: 1990ApJ...357..291D