A DEEP X-RAY IMAGE OF IC-2391

A 56 ks soft X-ray image of the IC 2391 star cluster has been acquired with the ROSAT High Resolution Imager, resulting in the detection of 34 sources above a 3 sigma detection level of L-X similar or equal to 4 x 10(28) ergs s(-1). We report source coordinates and fluxes plus id entifications and broadband BVRI photometry for optical counterparts t o each source. We compare these results with X-ray source fluxes from a ROSAT PSPC image of the same region, which we obtained 2 yr earlier. The largest change in X-ray brightness for any of the known or suspec ted G, K, and M cluster members is 0.43 dex, i.e., a factor of similar to 3. Given this modest amplitude in Xray variability, we conclude th at the broad (factor of 20) dispersion in X-ray luminosities within IC 2391 is unrelated to short-or intermediate-term cycles of the stellar dynamo. We further show that the effects of source confusion on the P SPC X-ray luminosity function, for distance scales of 5 ''-30 '', are relatively small and are thus negligible for the purpose of comparing IC 2391 with older clusters and for studying the evolution of coronal X-ray emission in solar-type stars. The greater part of the observed s catter in X-ray luminosity within IC 2391 still awaits explanation.