2005ApJ...624..923L

Archival IUE spectra of the VY Sculptoris system MV Lyrae, taken during an intermediate state, can be best fit by an isothermal accretion disk extending half-way to the tidal cutoff radius. In contrast, a recent HST spectrum, while MV Lyr was in a high state, can be best fit with a standard T(R) profile for an accretion disk extending from an inner truncation radius to an intermediate radius with an isothermal accretion disk beyond. These fits use component-star parameters determined from a study of MV Lyr in a low state. Model systems containing accretion disks with standard T(R) profiles have continua that are too blue. The observed high-state absorption-line spectrum exhibits excitation higher than provided by the T(R) profile, indicating likely line formation in a high-temperature region extending vertically above the accretion disk. The absorption lines show a blueshift and line broadening corresponding to formation in a low-velocity wind apparently coextensive with the high-temperature region. Lines of N V, Si IV, C IV, and He II are anomalously strong relative to our synthetic spectra, indicating possible composition effects, but unmodeled excitation effects could also produce the anomalies. An analysis of a low state of MV Lyr, considered in an earlier study and extended in this paper, sets a limit of 2500 K for the T_effof an accretion disk that may be present in the low state. This limit is in conflict with two recent models of the VY Sculptoris phenomenon.