The Evolution of Circumstellar Disks Surrounding Intermediate-mass Stars: IC 1805

Creators: Wolff, S. C.; Strom, S. E.; Rebull, L. M.

Abstract

We report the results of a study of the intermediate- and high-mass stars in the young, rich star-forming complex IC 1805, based on a combination of optical, near-infrared, and mid-infrared photometry, and classification spectra. These data provide the basis for characterizing the masses and ages for stars more massive than ~2 M_⊙ and enable a study of the frequency and character of circumstellar disks associated with intermediate- and high-mass stars. Optically thick accretion disks among stars with masses 2 < M/M_⊙ < 4 are rare (~2% of members) and absent among more massive stars. A larger fraction (~10%) of stars with masses 2 < M/M_⊙ < 4 appear to be surrounded by disks that have evolved from the initial optically thick accretion phase. We identify four classes of such disks. These classes are based on spectral energy distributions (SEDs) of excess emission above photospheric levels: disks that are (1) optically thin based on the magnitude of the observed excess emission from 2 to 24 μm, (2) optically thin in their inner regions (r < 20 AU) and optically thick in their outer regions, (3) exhibit empty inner regions (r < 10 AU) and optically thin emission in their outer regions, and (4) exhibit empty inner regions and optically thick outer regions. We discuss, and assess the merits and liabilities of, proposed explanations for disks exhibiting these SED types and suggest additional observations that would test these proposals.

Additional Information

© 2011 The American Astronomical Society. Received 2010 June 28; accepted 2010 September 19; published 2010 December 9. The authors thank Diane Harmer and Darryl Willmarth for making most of the spectroscopic observations at WIYN. We also thank Lori Allen, Uma Gorti, Lee Hartmann, David Hollenbach, Xavier Koening, Greg Laughlin, Doug Lin, and Joan Najita for a variety of stimulating discussions, insightful comments, and important critical remarks. We thank Jane Greaves for her generosity in offering access to her MIPS data during the early stages of this investigation. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research has made use of NASA's Astrophysics Data System (ADS) Abstract Service, and of the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation. These data were served by the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the Digitized Sky Surveys, which were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. The research described in this paper was partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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