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Published September 10, 2002 | Published
Journal Article Open

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


The h and χ Per "double cluster" is examined using wide-field (0°.98 × 0°.98) CCD UBV imaging supplemented by optical spectra of several hundred of the brightest stars. Restricting our analysis to near the cluster nuclei, we find 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 initial mass function slope for each of the cluster nuclei that is quite normal for high-mass stars, Γ = -1.3 ± 0.2, indistinguishable from a Salpeter value. We derive masses of 3700 M_☉ (h) and 2800 M_☉ (χ) integrating the present-day mass function from 1 to 120 M_☉. There is evidence of mild mass segregation within the cluster cores. Our data are consistent with the stars having formed at a single epoch; claims to the contrary are very likely due to the inclusion of the substantial population of early-type stars located at similar distances in the Perseus spiral arm, in addition to contamination by G and K giants at various distances. We discuss the uniqueness of the double cluster, citing other examples of such structures in the literature but concluding that the nearly identical nature of the two cluster cores is unusual. We fail to settle the long-standing controversy regarding whether or not the double cluster is the core of the Per OB1 association and argue that this may be unanswerable with current techniques. We also emphasize the need for further work on the pre-main-sequence population of this nearby and highly interesting region.

Additional Information

© 2002. The American Astronomical Society. Received 2002 February 27 Accepted 2002 May 18 Our interest in h and χ Per traces back to several conversations with Stephen Strom, who remarked at least once how hard it was to understand a 50 Myr age spread, lamenting that "if we do not understand star formation in h and χ Per, then where do we understand it?" We hope that we have partially addressed this concern. It is a pleasure to thank Michael Meyer and John Carpenter for work they did in measuring coordinates of the h and χ stars, which we used for spectroscopy prior to our CCD imaging efforts. We also acknowledge help and advice from George Jacoby in obtaining the Mosaic data. C. L. S. became involved in this project as a Research Experiences for Undergraduates participant in 1999, and her efforts were supported first by the National Science Foundation (NSF) under grant 99-88007 to Northern Arizona University and more recently by an NSF graduate research fellowship. We dedicate this paper to the memory of Bob Wildey, whose Ph.D. thesis on the subject of h/χ Per should be required reading for all students of Galactic astronomy.

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Published - Slesnick_2002_ApJ_576_880.pdf


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