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

D.C. Foster ¹ - A. Theissen¹ - C.J. Butler ¹ - W.R.J. Rolleston ² - P.B. Byrne ¹ - S.L. Hawley ³

1 - Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
e-mail: ath@star.arm.ac.uk
2 - Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, N. Ireland
3 - Department of Physics and Astronomy, Michigan State University, E. Lansing, Michigan 48824, U.S.A.

Abstract:

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.

Key words: stars: evolution -- stars: late-type -- open clusters: individual; stock 2