CCD photometry and proper motions of late–type stars in the young open cluster Stock 2

We present the results of the first CCD BVRI photometric and proper motion study of late-type stars in the young open cluster Stock 2. Twenty–one fields of approximately $5'\times 5'$ size have been observed photometrically, from which we have identified 118 candidate members based on their positions on colour–magnitude diagrams relative to theoretical isochrones. From a comparison of the known star density of the Pleiades, we estimate the contamination of this selection process due to background stars to be as large as $\sim50\%$. However, only 22 of those 118 candidate members have proper motions consistent with membership, suggesting that the contamination is of the order of $80\%$. Additional candidate members were found by means of a proper motion analysis of Schmidt plate material for a $3^{\circ}\times 3^{\circ}$ field containing the cluster. The cluster proper motion allows us to separate members from background and foreground stars. We have found 634 stars with a membership probability $\ge 50\%$ down to a limiting magnitude of $B \approx 20$, corresponding to late–M dwarfs at the distance of Stock 2.