The Star Formation History and Mass Function of the Double Cluster h and χ Persei

The h and Chi Per "double cluster" is examined using wide-field (0.98 deg x0.98 deg) CCD UBV imaging supplemented by optical spectra of several hundred ofthe brightest stars. Restricting our analysis to near the cluster nuclei, wefind identical reddenings (E(B-V)=0.56+/-0.01), distance moduli (11.85+/-0.05),and ages (12.8+/-1.0 Myr) for the two clusters. In addition, we find an IMFslope for each of the cluster nuclei that is quite normal for high-mass stars,Gamma=-1.3+/-0.2, indistinguishable from a Salpeter value. We derive masses of3700 M_Sun (h) and 2800 M_Sun (Chi) integrating the PDMF from 1 to 120 M_Sun.There is evidence of mild mass segregation within the cluster cores. Our dataare consistent with the stars having formed at a single epoch; claims to thecontrary are very likely due to the inclusion of the substantial population ofearly-type stars located at similar distances in the Perseus spiral arm, inaddition to contamination by G and K giants at various distances. We discussthe uniqueness of the double cluster, citing other examples of such structuresin the literature, but concluding that the nearly identical nature of the twocluster cores is unusual. We fail to settle the long-standing controversyregarding whether or not the double cluster is the core of the Per OB1association, and argue that this may be unanswerable with current techniques.We also emphasize the need for further work on the pre-main sequence populationof this nearby and highly interesting region.Comment: Accepted for publication in ApJ. 19 pages of text, 9 figures, 4 table