White Dwarfs in Cataclysmic Variables: IUE Archives and Synthetic Accretion Disk and Photospheric Spectra



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White Dwarfs in Cataclysmic Variables: IUE Archives and Synthetic Accretion Disk and Photospheric Spectra

Villanova undergraduates Dirk Fabian, Quyen Nguyen, and Kunegunde Belle with E.M. Sion and M. Huang, have been analyzing the IUE archival spectra of dwarf novae in quiescence and in outburst and nova-like variables in the low state. Their project involves line measurements and synthetic spectral fitting to determine temperatures, gravities and chemical abundances of the underlying white dwarfs. This work commenced during the summer of 1994 and is still in progress. A extensive grid of optically steady state, solar composition accretion disk models has been constructed by Nguyen and Belle using TLUSTY, SYNSPEC and DISKSYN for a broad range of accretion rates, disk inclinations and white dwarf masses. Analyses of TT Ari and MV Lyrae have been completed and will shortly be submitted for publication.

Nguyen, Fabian, Belle, Huang and Sion have constructed grids of white dwarf spectra with solar composition broadened by rotation. The rotational velocity of the white dwarf in a cataclysmic variable is critical for testing standard accretion disk/boundary layer theory, for studying the differential spinup of the white dwarf, and for the shear mixing and redistribution of matter and heat into and across the white dwarf surface. In many dwarf novae during quiescence, the white dwarf dominates the flux in the far ultraviolet. By observing these exposed degenerate stars with Hubble Space Telescope GHRS and FOS, the white dwarf rotation rates can be determined by fitting these synthetic spectra broadened by rotation. Using TLUSTY and SYNSPEC (Hubeny 1988), Nguyen, Belle, Fabian, Huang and Sion have presented a grid of rotationally broadened white dwarf synthetic spectra, convolved with the resolution of Hubble GHRS, FOS and IUE low resolution SWP spectra, computed for log g =8, solar composition, and T and 50,000K, and rotational velocities of 0 to 5000 km/s. Comparison of this synthetic spectral grid with spectra of exposed white dwarfs in cataclysmics can yield the actual rotational velocity of the underlying white dwarf or at least an upper limit constraint on V sin i from the observed profiles of photospheric absorption lines. Their soon to be published model grids demonstrate this capability.

Villanova undergraduates Daniel Griffith, Dirk Fabian and Sion have published their analysis of 15 IUE low resolution SWP spectra of the peculiar hot nova-like object BZ Camelopardis (= 0623+71), which is associated with a bow shock nebula (see Griffith, Fabian & Sion 1995).



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Next: Hubble Space Telescope Up: CURRENT RESEARCH Previous: Fully Convective M



Astronomy
Mon Feb 26 18:11:01 EST 1996