The rise and fall of debris disks: MIPS observations of h and χ Persei and the evolution of mid-IR emission from planet formation

We describe Spitzer MIPS observations of the double cluster, h and χ Persei, covering a ∼0.6 deg² area surrounding the cores of both clusters. The data are combined with IRAC and 2MASS data to investigate ∼616 sources from 1.25-24 μm. We use the long-baseline K_s - [24] color to identify two populations with IR excess indicative of circumstellar material: Be stars with 24 μm excess from optically thin free-free emission, and 17 fainter sources (J ∼ 14-15) with [24] excess consistent with a circumstellar disk. The frequency of IR excess for the fainter sources increases from 4.5 to 24 μm. The IR excess is likely due to debris from the planet formation process. The wavelength-dependent behavior is consistent with an inside-out clearing of circumstellar disks. A comparison of the 24 μm excess population in h and χ Per sources with results for other clusters shows that 24 μm emission from debris disks "rises" from 5 to 10 Myr, peaks at ∼10-15 Myr, and then "falls" from ∼15-20 Myr to 1 Gyr.