Lawler, S. M. and Herbst, W. and Redfield, S. and Hamilton, C. M. and Johns-Krull, C. M. and Winn, J. N. and Johnson, J. A. and Mundt, R. (2010) Gas absorption in the KH 15D system: Further evidence for dust settling in the circumbinary disk. Astrophysical Journal, 711 (2). pp. 1297-1305. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20100316-143441474
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Na I D lines in the spectrum of the young binary KH 15D have been analyzed in detail. We find an excess absorption component that may be attributed to foreground interstellar absorption, and to gas possibly associated with the solids in the circumbinary disk. The derived column density is log N_(Na I) = 12.5 cm^(−2), centered on a radial velocity that is consistent with the systemic velocity. Subtracting the likely contribution of the interstellar medium leaves log N_(Na I) ~ 12.3 cm^(−2). There is no detectable change in the gas column density across the “knife edge” formed by the opaque grain disk, indicating that the gas and solids have very different scale heights, with the solids being highly settled. Our data support a picture of this circumbinary disk as being composed of a very thin particulate grain layer composed of millimeter-sized or larger objects that are settled within whatever remaining gas may be present. This phase of disk evolution has been hypothesized to exist as a prelude to the formation of planetesimals through gravitational fragmentation, and is expected to be short-lived if much gas were still present in such a disk. Our analysis also reveals the presence of excess Na I emission relative to the comparison spectrum at the radial velocity of the currently visible star that plausibly arises within the magnetosphere of this still-accreting young star.
|Additional Information:||© 2010 The American Astronomical Society. Received 2009 October 19; accepted 2010 February 2; published 2010 February 23. We thank Coryn Bailer-Jones for some of the VLT/UVES data, and Suzan Edwards for the spectrum of LkCa 7. S.M.L. thanks Roy Kilgard and Peter Plavchan for very helpful advice and discussions regarding this paper. W.H. acknowledges support by NASA through the Origins of the Solar Systems grant NNX08AK35G. C.M.J.-K. acknowledges partial support by NASA through Origins of the Solar Systems grant NNX08AH86G. J.N.W. gratefully acknowledges the support of the MIT Class of 1942 Career Development Professorship. J.A.J. acknowledges support from NSF grant AST-0702821. Some of 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 the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The Hobby-Eberly Telescope (HET) is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universitat Munchen, and Georg-August-Universitat Gottingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly. This paper is based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (Program 074.C- 0604A). Facilities: HET (HRS), Keck:I (HIRES), VLT:Kueyen (UVES).|
|Subject Keywords:||circumstellar matter; stars: individual (KH 15D); stars: pre-main sequence|
|Classification Code:||PACS: 97.80.Fk; 97.10.Fy; 97.10.Wn; 97.10.Ri; 97.80.Hn.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||20 Mar 2010 03:20|
|Last Modified:||26 Dec 2012 11:50|
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