A Deep Spitzer Survey of Circumstellar Disks in the Young Double Cluster, h and χ Persei

Cloutier, Ryan and Currie, Thayne and Rieke, George H. and Kenyon, Scott J. and Balog, Zoltán and Jayawardhana, Ray (2014) A Deep Spitzer Survey of Circumstellar Disks in the Young Double Cluster, h and χ Persei. ASTROPHYSICAL JOURNAL, 796. ISSN 1538-4357

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Abstract

We analyze very deep IRAC and MIPS photometry of ∼ 12, 500 members of the 14 Myr old Double Cluster, h and χ Persei, building upon on our earlier, shallower Spitzer Cycle 1 studies (Currie et al. 2007, Currie et al. 2008). Numerous likely members show infrared (IR) excesses at 8 μm and 24 μm indicative of circumstellar dust. The frequency of stars with 8 μm excess is at least 2% for our entire sample, slightly lower (higher) for B/A stars (later type, lower-mass stars). Optical spectroscopy also identifies gas in about 2 % of systems but with no clear trend between the presence of dust and gas. Spectral energy distribution (SED) modeling of 18 sources with detections at optical wavelengths through MIPS 24 μm reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, although similar data for all disk-bearing members would provide constraints. Using Monte Carlo simulations, we combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nominal cluster ages, the e-folding times (τ0) for the frequency of warm dust and gas are 2.75 Myr and 1.75 Myr respectively. Assuming a revised set of ages for some clusters (e.g. Bell et al. 2013), these timescales increase to 5.75 and 3.75 Myr, respectively, implying a significantly longer typical protoplanetary disk lifetime than previously thought. In both cases the transitional disk duration, averaged over multiple evolutionary pathways, is ≈ 1 M yr. Finally, 24 μm excess frequencies for 4–6 M⊙ stars appear lower than for 1–2.5 M⊙ stars in other 10–30 M yr old clusters.

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