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High-resolution 5 μm Spectroscopy of Transitional Disks

Salyk, C. and Blake, G. A. and Boogert, A. C. A. and Brown, J. M. (2009) High-resolution 5 μm Spectroscopy of Transitional Disks. Astrophysical Journal, 699 (1). pp. 330-347. ISSN 0004-637X.

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We present high-resolution M-band (~5 μm) spectra of 14 transitional disks—circumstellar disks with an optically thick outer zone but an inner region significantly depleted of small dust grains—obtained with NIRSPEC on the Keck II telescope. We detect CO emission from nine disks, and show that for the majority of these systems, the emission originates in the depleted inner disk region. We find that the presence of high 5 μm veiling, strong CO emission, and high accretion rates are usually correlated, suggesting that at least two classes of transitional disks exist—those nearly completely cleared, and those only partially depleted, within their transition radius. Cleared inner disks are consistent with the presence of a close stellar companion, or with formation by photoevaporation. Of the cleared transitional disks, at least two (HD 98800 B and CoKu Tau/4) are known to be circumbinary with projected binary separations of several AU or less. Partially depleted inner disks most often have CO that extends to small (≾1 AU) radii, but compared to "classical" disks the CO excitation temperature is lower and the emission radii are larger than that expected for dust sublimation. These disks are consistent with the presence of a giant planet, and inconsistent with having been formed by photoevaporation. Although the inner regions of such disks are vertically optically thin in dust emission, line-of-sight opacities from the star can be large, and the complex physical and chemical processes therein make it difficult to derive a fiducial CO abundance with respect to molecular hydrogen. Thus, CO M-band lines are best suited to providing lower bounds as to the total inner disk gas mass. Amongst the partially depleted sources, veiling measurements and CO emission models demonstrate a great diversity of inner disk gas content and gas/dust ratios, suggesting a variety of planet-forming environments.

Item Type:Article
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Salyk, C.0000-0003-3682-6632
Blake, G. A.0000-0003-0787-1610
Additional Information:© 2009 The American Astronomical Society. Received 2008 December 22; accepted 2009 April 27; published 2009 June 11. The authors thank the anonymous referee for a careful reading of this manuscript, and acknowledge support from the NASA SIRTF and Origins programs. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work was also based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership. In addition, this work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASA Space Infrared Telescope FacilityUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Association of Universities for Research in Astronomy (AURA)UNSPECIFIED
Subject Keywords:planetary systems: protoplanetary disks; stars: pre-main sequence
Issue or Number:1
Record Number:CaltechAUTHORS:20090908-135707389
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Official Citation:High-resolution 5 μm Spectroscopy of Transitional Disks C. Salyk, G. A. Blake, A. C. A. Boogert, and J. M. Brown 2009 ApJ 699 330-347 doi: 10.1088/0004-637X/699/1/330.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15676
Deposited By: Tony Diaz
Deposited On:15 Sep 2009 16:05
Last Modified:09 Dec 2019 22:00

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