First ultraviolet observations of the transition regions of X-ray bright solar-type stars in the Pleiades

Abstract

Nearby clusters, such as Ursa Major, the Hyades, and the Pleiades, have been extensively studied in the X-ray regime. The first two clusters have also been studied with the IUE. However, the younger, fainter Pleiades cluster, which contains the youngest, and presumably most active, main sequence stars in the solar vicinity, had not been observed in the ultraviolet. Observations of such young clusters provide the best method of studying the evolution of stellar parameters as a star ages on the main sequence. Hence, we present here the first ultraviolet study of the transition regions of two X-ray bright solar-type stars from the Pleiades in an attempt to extend the main sequence age baseline for the transition region activity-age relation over more than two orders of magnitude. However, no emission lines were detected from either star; the upper limits to the fluxes are consistent with previously determined saturation levels, but do not help to further constrain evolutionary models.