Ultraviolet photometry form the Orbiting Astronomical Observatory. VII. alpha 2 Canum Venaticorum.

Far-ultraviolet photometry by OAO-2 is presented for a2 CVn covering the entire 5d47 period of this magnetic Ap variable. The light curves ranging from Al 330 to A3320 indicate that there are two important sources of back warming from far-ultraviolet absorption. Strong line blanketing by the rare earths redistributes flux longward of the Balmer discontinuity, causing the major observed photometric variations. In addition, a second source, which may be due to a combination of continuous opacities and line blanketing from the iron-peak and rare-earth groups below Al 600, apparently redistributes flux into the region of the Balmer discontinuity. It is also found that ground-based determinations of the effective temperature are overestimated due to the flux redistribution from far-ultraviolet absorption. The effective temperature of a2 CYn derived from OAO and ground-based absolute fluxes is found to be 11,200 K, which remains constant over the cycle. Subject headings: magnetic stars opacities peculiar A stars spectra, ultraviolet - stars, individual ultraviolet