Spitzer Observations of the λ Orionis Cluster. I. The Frequency of Young Debris Disks at 5 Myr
Abstract
We present IRAC/MIPS Spitzer observations of intermediate-mass stars in the 5 Myr old λ Orionis cluster. In a representative sample of stars earlier than F5 (29 stars), we find a population of nine stars with varying degree of moderate 24 μm excess comparable to those produced by debris disks in older stellar groups. As expected in debris disks systems, those stars do not exhibit emission lines in their optical spectra. We also include in our study the star HD 245185, a known Herbig Ae object which displays excesses in all Spitzer bands and shows emission lines in its spectrum. We compare the disk population in the λ Orionis cluster with the disk census in other stellar groups studied using similar methods to detect and characterize their disks and spanning a range of ages from 3 Myr to 10 Myr. We find that for stellar groups of 5 Myr or older the observed disk frequency in intermediate-mass stars (with spectral types from late B to early F) is higher than in low-mass stars (with spectral types K and M). This is in contradiction with the observed trend for primordial disk evolution, in which stars with higher stellar masses dissipate their primordial disks faster. At 3 Myr, the observed disk frequency in intermediate-mass stars is still lower than for low-mass stars indicating that second generation dusty disks start to dominate the disk population at 5 Myr for intermediate-mass stars. This result agrees with recent models of evolution of solids in the region of the disk where icy objects form (>30 AU), which suggest that at 5-10 Myr collisions start to produce large amount of dust during the transition from runaway to oligarchic growth (reaching sizes of ~500 km) and then dust production peaks at 10-30 Myr, when objects reach their maximum size (≥1000 km).
Additional Information
© 2009 The American Astronomical Society. Received 2009 June 8; accepted 2009 October 22; published 2009 November 25. We thank Thayne Currie and Maria Morales Calderon for insightful communications, and the anonymous referee for input that greatly improved this manuscript. This work is based on observations made with the Spitzer Space Telescope (GO-1 0037), which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. J.H. and N.C. gratefully acknowledge support from the NASA Origins program and the Spitzer General Observer program.Attached Files
Published - Hernandez2009p6574Astrophys_J.pdf
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Additional details
- Eprint ID
- 17066
- Resolver ID
- CaltechAUTHORS:20100105-141417070
- NASA
- Spitzer Science Center
- Created
-
2010-01-06Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)