Poteet, Charles A. and Megeath, S. Thomas and Watson, Dan M. and Calvet, Nuria and Remming, Ian S. and McClure, Melissa K. and Sargent, Benjamin A. and Fischer, William J. and Furlan, Elise and Allen, Lori E. and Bjorkman, Jon E. and Hartmann, Lee and Muzerolle, James and Tobin, John J. and Ali, Babar (2011) A Spitzer Infrared Spectrograph Detection of Crystalline Silicates in a Protostellar Envelope. Astrophysical Journal Letters, 733 (2). Art. No. L32. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110902-081218228
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We present the Spitzer Space Telescope Infrared Spectrograph spectrum of the Orion A protostar HOPS-68. The mid-infrared spectrum reveals crystalline substructure at 11.1, 16.1, 18.8, 23.6, 27.9, and 33.6 μm superimposed on the broad 9.7 and 18 μm amorphous silicate features; the substructure is well matched by the presence of the olivine end-member forsterite (Mg_2SiO_4). Crystalline silicates are often observed as infrared emission features around the circumstellar disks of Herbig Ae/Be stars and T Tauri stars. However, this is the first unambiguous detection of crystalline silicate absorption in a cold, infalling, protostellar envelope. We estimate the crystalline mass fraction along the line of sight by first assuming that the crystalline silicates are located in a cold absorbing screen and secondly by utilizing radiative transfer models. The resulting crystalline mass fractions of 0.14 and 0.17, respectively, are significantly greater than the upper limit found in the interstellar medium (≾0.02-0.05). We propose that the amorphous silicates were annealed within the hot inner disk and/or envelope regions and subsequently transported outward into the envelope by entrainment in a protostellar outflow.
|Additional Information:||© 2011 The American Astronomical Society. Received 2010 August 20; accepted 2011 April 14; published 2011 May 10. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. This work was supported by NASA through contract number 1289605 issued by JPL/Caltech. C.A.P. thanks Henrik Spoon and Adwin Boogert for insightful discussions.|
|Subject Keywords:||circumstellar matter; infrared: stars; stars: formation; stars: individual (FIR-2); stars: protostars|
|Classification Code:||PACS: 97.21.+a; 97.10.Fy; 97.10.Tk; 95.85.Hp; 98.38.Dq; 97.10.Cv|
|Official Citation:||A Spitzer Infrared Spectrograph Detection of Crystalline Silicates in a Protostellar Envelope Charles A. Poteet et al. 2011 ApJ 733 L32|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||02 Sep 2011 19:13|
|Last Modified:||26 Dec 2012 13:39|
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