Characterization of the Praesepe Star Cluster by Photometry and Proper Motions with 2MASS, PPMXL, and Pan-STARRS

P. F. Wang, W. P. Chen, C. C. Lin, A. K. Pandey, C. K. Huang, N. Panwar, C. H. Lee, M. F. Tsai, C. -H. Tang, B. Goldman, W. S. Burgett, K. C. Chambers, P. W. Draper, H. Flewelling, T. Grav, J. N. Heasley, K. W. Hodapp, M. E. Huber, R. Jedicke, N. Kaiser, R. -P. Kudritzki, G. A. Luppino, R. H. Lupton, E. A. Magnier, N. Metcalfe, D. G. Monet, J. S. Morgan, P. M. Onaka, P. A. Price, C. W. Stubbs, W. Sweeney, J. L. Tonry, R. J. Wainscoat, C. Waters

Published 2014-01-29Version 1

Membership identification is the first step to determine the properties of a star cluster. Low-mass members in particular could be used to trace the dynamical history, such as mass segregation, stellar evaporation, or tidal stripping, of a star cluster in its Galactic environment. We identified member candidates with stellar masses $\sim$0.11--2.4 Msun of the intermediate-age Praesepe cluster (M44), by using Pan-STARRS and 2MASS photometry, and PPMXL proper motions. Within a sky area of 3 deg radius, 1040 candidates are identified, of which 96 are new inclusions. Using the same set of selection criteria on field stars led to an estimate of a false positive rate 16%, suggesting 872 of the candidates being true members. This most complete and reliable membership list allows us to favor the BT-Settl model in comparison with other stellar models. The cluster shows a distinct binary track above the main sequence, with a binary frequency of 20--40%, and a high occurrence rate of similar mass pairs. The mass function is consistent with that of the disk population but shows a deficit of members below 0.3 solar masses. A clear mass segregation is evidenced, with the lowest-mass members in our sample being evaporated from this disintegrating cluster.