A SPITZER SURVEY OF PROTOPLANETARY DISK DUST IN THE YOUNG SERPENS CLOUD: HOW DO DUST CHARACTERISTICS EVOLVE WITH TIME?
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
- California Institute of Technology, Division for Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125 (United States)
- Herschel Science Center, European Space Agency (ESA), P.O. Box 78, 28691 Villanueva de la Canada (Madrid) (Spain)
- University of Toronto, 50 St. George St., Toronto, ON M5R 2W9 (Canada)
- Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Oester Voldgade 5-7, DK-1350 Copenhagen (Denmark)
- Laboratoire d'Astrophysique de Grenoble, Universite Joseph Fourier, CNRS, UMR 5571, Grenoble (France)
We present Spitzer InfraRed Spectrograph (IRS) mid-infrared (5-35 {mu}m) spectra of a complete flux-limited sample ({>=}3 mJy at 8 {mu}m) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and classified. Background stars (with slope consistent with a reddened stellar spectrum and silicate features in absorption), galaxies (with redshifted polycyclic aromatic hydrocarbon (PAH) features), and a planetary nebula (with high ionization lines) amount to 22% of contamination in this sample, leaving 115 true YSOs. Sources with rising spectra and ice absorption features, classified as embedded Stage I protostars, amount to 18% of the sample. The remaining 82% (94) of the disk sources are analyzed in terms of spectral energy distribution shapes, PAHs, and silicate features. The presence, strength, and shape of these silicate features are used to infer disk properties for these systems. About 8% of the disks have 30/13 {mu}m flux ratios consistent with cold disks with inner holes or gaps, and 3% of the disks show PAH emission. Comparison with models indicates that dust grains in the surface of these disks have sizes of at least a few {mu}m. The 20 {mu}m silicate feature is sometimes seen in the absence of the 10 {mu}m feature, which may be indicative of very small holes in these disks. No significant difference is found in the distribution of silicate feature shapes and strengths between sources in clusters and in the field. Moreover, the results in Serpens are compared with other well-studied samples: the c2d IRS sample distributed over five clouds and a large sample of disks in the Taurus star-forming region. The remarkably similar distributions of silicate feature characteristics in samples with different environment and median ages-if significant-imply that the dust population in the disk surface results from an equilibrium between dust growth and destructive collision processes that are maintained over a few million years for any YSO population irrespective of environment.
- OSTI ID:
- 21448889
- Journal Information:
- Astrophysical Journal, Vol. 714, Issue 1; Other Information: DOI: 10.1088/0004-637X/714/1/778; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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