Ultraviolet photometry from the Orbiting Astronomical Observatory. XXVII. Interpretation of the light curve of RR Lyrae.

The OAO-2 ultraviolet RR Lyr light curves are presented. A hydrodynamical model is used to show the influence of atmospheric shock waves on these light curves. We find the ultraviolet observations to be useful as a verification of hydrodynamic atmospheric models, especially at the shortest wavelengths where the ultraviolet radiation tends to probe regions above the visible-light photo sphere. Our model indicates that visible light observations of the bump in the light curve before rising light and the stillstand in rising light are due to the energy deposition by two separate shock waves. Subject headings: hydrodynamics - stars: atmospheres - stars: RR Lyrae - ultraviolet: general