BV photometry and Hα spectroscopy of the RS Canum Venaticorum binary UX Arietis.

Abstract

We present differential BV photometry of UX Ari obtained on 76 nights during 1989-94 and Hα spectroscopy obtained on 14 nights during the 1990-91 observing season. The migration of the phase of light minimum indicates a life-time longer than 20 years for the starspots located at synchronous latitudes and a life-time in the range 2-8 years for those located at faster rotating latitudes. UX Ari is bluer at light minimum than at light maximum. We interpret this as due to an increase in the fractional contribution in the blue spectral region from the hotter secondary as the cool active star becomes faint. The amplitude shows a modulation with a period around 10-13 years, apparently anticorrelated with the brightness at light minimum. Lower amplitudes occur when the spots are more evenly distributed longitudinally rather than when the levels of spot activity are less. The mean brightness also varies, but with a time-scale longer than 20 years. The Hα emission equivalent width does not show any significant phase modulation. The measured Hα equivalent widths of both components are, most likely, affected by variations in their relative continuum levels as the active star varies.