THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. I. A CENSUS OF DUSTY YOUNG STELLAR OBJECTS AND A STUDY OF THEIR MID-INFRARED VARIABILITY
- Department of Physics and Astronomy, University of Toledo, Toledo, OH 43560 (United States)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
- Harvard Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
- National Optical Astronomical Observatory, Tucson, AZ 85719 (United States)
- Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)
- Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)
- Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments on board Spitzer. In total, five distinct fields were mapped, covering 9 deg{sup 2} in five mid-IR bands spanning 3-24 {mu}m. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630, and 1622 dark clouds, and the NGC 2023, 2024, 2068, and 2071 nebulae. These data are merged with the Two Micron All Sky Survey point source catalog to generate a catalog of eight-band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main-sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in two to three epochs over six months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5 {mu}m bands. We find that 50% of the dusty YSOs show variability. The variations are typically small ({approx}0.2 mag) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8, and 8 {mu}m variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots.
- OSTI ID:
- 22089773
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 144, Issue 6; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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