X-ray sources in regions of star formation. VI. The R CRA association as viewed by Einstein

We report on optical identifications of X-ray sources in the vicinity of the R CrA association. We identify 11 low-mass pre-main-sequence stars as counterparts of 9 X-ray sources. We also find X-ray emission from coordinates consistent with the position of 3 bright late-B stars, although the emission may come from lower mass companions. The X-ray-selected stars lie along a narrow locus in the luminosity-temperature diagram at an age of about 7 Myr, which is considerably older than the estimated ages of the higher mass stars or of the IR-excess stars. We determine the physical characteristics of these stars, including masses, ages, and Lithium abundances. We estimate that the complete membership of the R CrA association amounts to about 90 stars, mostly older naked T Tauri stars, and that the population is consistent with the standard IMF.