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Published June 10, 2009 | Published
Journal Article Open

The Last Gasp of Gas Giant Planet Formation: A Spitzer Study of the 5 Myr Old Cluster NGC 2362

Abstract

Expanding upon the Infrared Array Camera (IRAC) survey from Dahm & Hillenbrand, we describe Spitzer IRAC and Multiband Imaging Photometer for Spitzer observations of the populous, 5 Myr old open cluster NGC 2362. We analyze the mid-IR colors of cluster members and compared their spectral energy distributions (SEDs) to star+circumstellar disk models to constrain the disk morphologies and evolutionary states. Early/intermediate-type confirmed/candidate cluster members either have photospheric mid-IR emission or weak, optically thin IR excess emission at λ ≥ 24 μm consistent with debris disks. Few late-type, solar/subsolar-mass stars have primordial disks. The disk population around late-type stars is dominated by disks with inner holes (canonical "transition disks") and "homologously depleted" disks. Both types of disks represent an intermediate stage between primordial disks and debris disks. Thus, in agreement with previous results, we find that multiple paths for the primordial-to-debris disk transition exist. Because these "evolved primordial disks" greatly outnumber primordial disks, our results undermine standard arguments in favor of a ≾10^5 yr timescale for the transition based on data from Taurus-Auriga. Because the typical transition timescale is far longer than 10^5 yr, these data also appear to rule out standard ultraviolet photoevaporation scenarios as the primary mechanism to explain the transition. Combining our data with other Spitzer surveys, we investigate the evolution of debris disks around high/intermediate-mass stars and investigate timescales for giant planet formation. Consistent with Currie et al., the luminosity of 24 μm emission in debris disks due to planet formation peaks at ≈10-20 Myr. If the gas and dust in disks evolve on similar timescales, the formation timescale for gas giant planets surrounding early-type, high/intermediate-mass (≾1.4 M_⊙ ) stars is likely 1-5 Myr. Most solar/subsolar-mass stars detected by Spitzer have SEDs that indicate their disks may be actively leaving the primordial disk phase. Thus, gas giant planet formation may also occur by ~5 Myr around solar/subsolar-mass stars as well.

Additional Information

© 2009. The American Astronomical Society. Print publication: Issue 1 (2009 June 10). Received 2008 August 27, accepted for publication 2009 March 15. Published 2009 May 19. We thank Richard Alexander for useful comments about UV photoevaporation and Adam Kraus for very informative discussions on the role of binarity in disk evolution. We also thank Carol Grady for pointing out constraints on the formation of Saturn from the planetary science community. Support for this work was provided by NASA through the Spitzer Space Telescope Fellowship Program (TPR). Facility: Spitzer Space Telescope

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August 21, 2023
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