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Properties of Protostars in the Elephant Trunk in the Globule IC 1396A

Reach, William T. and Faied, Dohy and Rho, Jeonghee and Boogert, Adwin and Tappe, Achim and Jarrett, Thomas H. and Morris, Patrick and Cambrésy, Laurent and Palla, Francesco and Valdettaro, Riccardo (2009) Properties of Protostars in the Elephant Trunk in the Globule IC 1396A. Astrophysical Journal, 690 (1). pp. 683-705. ISSN 0004-637X. doi:10.1088/0004-637X/690/1/683.

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Extremely red objects, identified in the early Spitzer Space Telescope observations of the bright-rimmed globule IC 1396A and photometrically classified as Class I protostars and Class II T Tauri stars based on their mid-infrared (mid-IR) colors, were spectroscopically observed at 5.5-38 μm (Spitzer Infrared Spectrograph), at the 22 GHz water maser frequency (National Radio Astronomy Observatory Green Bank Telescope), and in the optical (Palomar Hale 5 m) to confirm their nature and further elucidate their properties. The sources photometrically identified as Class I, including IC 1396A:α, γ, δ, ε, and ζ, are confirmed as objects dominated by accretion luminosity from dense envelopes, with accretion rates 1-10 × 10^–6 M☉ yr^–1 and present stellar masses 0.1-2 M☉. The Class I sources have extremely red continua, still rising at 38 μm, with a deep silicate absorption at 9-11 μm, weaker silicate absorption around 18 μm, and weak ice features including CO2 at 15.2 μm and H2O at 6 μm. The ice/silicate absorption ratio in the envelope is exceptionally low for the IC 1396A protostars, compared to those in nearby star-forming regions, suggesting that the envelope chemistry is altered by the radiation field or globule pressure. Only one 22 GHz water maser was detected in IC 1396A; it is coincident with a faint mid-IR source, offset from near the luminous Class I protostar IC 1396A:γ. The maser source, IC 1396A:γb, has luminosity less than 0.1 L☉, the first H2O maser from such a low-luminosity object. Two near-infrared (NIR) H2 knots on opposite sides of IC 1396A:γ reveal a jet, with an axis clearly distinct from the H2O maser of IC 1396A:γb. The objects photometrically classified as Class II, including IC 1396A:β, θ, Two Micron All Sky Survey (2MASS)J 21364964+5722270, 2MASSJ 21362507+5727502, LkHα 349c, Tr 37 11-2146, and Tr 37 11-2037, are confirmed as stars with warm, luminous disks, with a silicate emission feature at 9-11 μm, and bright Hα emission; therefore, they are young, disk-bearing, classical T Tauri stars. The disk properties change significantly with source luminosity: low-mass (G-K) stars have prominent 9-11 emission features due to amorphous silicates while higher-mass (A-F) stars have weaker features requiring abundant crystalline silicates. A mineralogical model that fits the wide- and low-amplitude silicate feature of IC 1396A:θ requires small grains of crystalline olivine (11.3 μm peak) and another material to to explain its 9.1 μm peak; reasonable fits are obtained with a phyllosilicate, quartz, or relatively large (greater than 10 μm) amorphous olivine grains. The distribution of Class I sources is concentrated within the molecular globule, while the Class II sources are more widely scattered. Combined with the spectral results, this suggests two phases of star formation, the first (4 Myr ago) leading to the widespread Class II sources and the central O star of IC 1396 and the second (less than 1 Myr ago) occurring within the globule. The recent phase was likely triggered by the wind and radiation of the central O star of the IC 1396 H II region.

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Reach, William T.0000-0001-8362-4094
Rho, Jeonghee0000-0003-3643-839X
Jarrett, Thomas H.0000-0002-4939-734X
Additional Information:© 2009 The American Astronomical Society. Received 2008 May 15, accepted for publication 2008 August 27. Published 2008 December 1. Print publication: Issue 1 (2009 January 1). W.T.R. gratefully acknowledges exceptionally valuable discussions with B. Elmegreen regarding the dynamics of the globule. G. Blake is thanked for assistance in obtaining the Keck/NIRSPEC L-band spectra. This work is based in part on observations made with the SST, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. This work is also based in part on observations obtained at the Hale Telescope, Palomar Observatory as part of a continuing collaboration between the California Institute of Technology, NASA/JPL, and Cornell University. 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. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.
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W. M. Keck FoundationUNSPECIFIED
Subject Keywords:infrared: stars; ISM: globules; ISM: individual (IC 1396A); planetary systems: protoplanetary discs
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Record Number:CaltechAUTHORS:REAapj09
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ID Code:12517
Deposited By: Archive Administrator
Deposited On:12 Dec 2008 04:33
Last Modified:08 Nov 2021 22:29

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