SpitzerIRAC andJHKsObservations of h and χ Persei: Constraints on Protoplanetary Disk and Massive Cluster Evolution at ∼107Years

We describe IRAC 3.6-8 mu_m observations and ground-based near-IR JHKsphotometry from Mimir and 2MASS of the massive double cluster h & chi Perseicomplete to J=15.5 (M ~ 1.3 Msun. Within 25' of the cluster centers we detect\~11,000 sources with J < 15.5, ~7,000 sources with [4.5] < 15, and ~ 5000sources with [8] < 14.5. In both clusters, the surface density profiles derivedfrom the 2MASS data decline with distance from the cluster centers as expectedfor a bound cluster. Within 15' of the cluster centers, ~ 50% of the stars lieon a reddened ~ 13 Myr isochrone; at 15'-25' from the cluster centers, ~ 40%lie on this isochrone. Thus, the optical/2MASS color-magnitude diagramsindicate that h & chi Per are accompanied by a halo population with roughly thesame age and distance as the two dense clusters. The double cluster lacks anyclear IR excess sources for J < 13.5 (~ 2.7 Msun). Therefore, disks aroundhigh-mass stars disperse prior to ~ 10^{7} yr. At least 2-3% of the faintercluster stars have strong IR excess at both [5.8] and [8]. About 4-8% ofsources slightly more massive than the Sun (~ 1.4 Msun) have IR excesses at[8]. Combined with the lack of detectable excesses for brighter stars, thisresult suggests that disks around lower-mass stars have longer lifetimes. TheIR excess population also appears to be larger at longer IRAC bands ([5.8],[8]) than at shorter IRAC/2MASS bands ($K_{s}$, [4.5]), a result consistentwith an inside-out clearing of disks.Comment: matched to published version, 26 pages, 18 figures: 2007, ApJ, 659, 59