New Light on Young Stars:
Spitzer's View of Circumstellar Disks

Mid-infrared Spectra of the Transitional Disks of the Orion A Cloud

First Author:
KyoungHee Kim
Email: khkim AT pas.rochester.edu
University of Rochester
Department of Physics and Astronomy, University of Rochester
Rochester/NY, 14627, USA
Coauthors:
Watson, Dan, University of Rochester
Manoj, Puravankara, University of Rochester
Forrest, William, University of Rochester
Sargent, Ben, STScI
Furlan, Elise, JPL
Calvet, Nuria, University of Michigan
Espaillat, Catherine, University of Michigan
McClure, Melissa, University of Michigan
Harrold, Samuel, University of Rochester
Allen, Lori, Harvard-Smithsonian CfA
Muzerolle, James, University of Arizona, Steward Observatory
Megeath, Tom, University of Toledo

Abstract
We present 5-40 micron Spitzer Infrared Spectrograph spectra of the transitional disks in the Orion A molecular-cloud complex. Transitional disks -- T Tau stars with little excess at short infrared wavelengths but excesses similar to ordinary Class II YSOs at longer wavelengths -- are thought to owe their distinctive spectral energy distributions (SEDs) to wide central holes or gaps in YSO disks. Here we extend our study of these objects in the nearest star-forming regions to the Orion clouds, a sample twice as large as that in the Tau-Aur-Cha-Oph regions. We identified 34 new transitional disks in Orion A. We compare the SEDs of transitional disks with the median SED of Class II YSOs in Orion A, and assess the disk structures and properties with simple models. We also compare the characteristics of the transitional disks in Orion A with those found in the nearest clouds, to shed light on differences in the evolution of these objects in the variety of star-forming environments found in Orion.

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