The CFHT Open Star Cluster Survey. IV. Two Rich, Young Open Star Clusters: NGC 2168 (M35) and NGC 2323 (M50)

We continue our study of rich Galactic clusters by presenting deep CCDobservations of both NGC 2168 (M35) and NGC 2323 (M50). Both clusters are foundto be rich (NGC 2168 contains at least 1000 stars brighter than V = 22 and NGC2323 contains approximately 2100 stars brighter than our photometric limit of V= 23) and young (age of NGC 2168 = 180 Myrs, age of NGC 2323 = 130 Myrs). Thecolor-magnitude diagrams for the clusters exhibit clear main sequencesstretching over 14 magnitudes in the V, B-V plane. Comparing these long mainsequences with those of earlier clusters in the survey, as well as with theHyades, has allowed for accurate distances to be established for each cluster(dist. of NGC 2168 = 912 +/- 70/65 pc, dist. of NGC 2323 = 1000 +/- 81/75 pc).Analysis of the luminosity and mass functions suggest that despite their youngages, both clusters are somewhat dynamically relaxed exhibiting signs ofmass-segregation. This is especially interesting in the case of NGC 2323, whichhas an age of only 1.3 times the dynamical relaxation time. The presentphotometry is also deep enough to detect all of the white dwarfs in bothclusters. We discuss some interesting candidates which may be the remnants ofquite massive (M > 5 Mo) progenitor stars. The white dwarf cooling age of NGC2168 is found to be in good agreement with the main-sequence turn-off age.These objects are potentially very important for setting constraints on thewhite dwarf initial-final mass relationship and upper mass limit for whitedwarf production.Comment: 34 pages, including 12 diagrams and 5 tables. Accepted for publication in AJ. Minor typos correcte