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c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines

Lahuis, F. and van Dishoeck, E. F. and Jørgensen, J. K. and Blake, G. A. and Evans, N. J., II (2010) c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines. Astronomy and Astrophysics, 519 . A3. ISSN 0004-6361.

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Context. A survey of mid-infrared gas-phase emission lines of H_2, H_(2)O and various atoms toward a sample of 43 embedded low-mass young stars in nearby star-forming regions is presented. The sources are selected from the Spitzer “Cores to Disks” (c2d) legacy program. Aims. The environment of embedded protostars is complex both in its physical structure (envelopes, outflows, jets, protostellar disks) and the physical processes (accretion, irradiation by UV and/or X-rays, excitation through slow and fast shocks) which take place. The mid-IR spectral range hosts a suite of diagnostic lines which can distinguish them. A key point is to spatially resolve the emission in the Spitzer-IRS spectra to separate extended PDR and shock emission from compact source emission associated with the circumstellar disk and jets. Methods. An optimal extraction method is used to separate both spatially unresolved (compact, up to a few hundred AU) and spatially resolved (extended, thousand AU or more) emission from the IRS spectra. The results are compared with the c2d disk sample and literature PDR and shock models to address the physical nature of the sources. Results. Both compact and extended emission features are observed. Warm (T_(ex) few hundred K) H_2, observed through the pure rotational H_2 S(0), S(1) and S(2) lines, and [S i] 25 μm emission is observed primarily in the extended component. [S i] is observed uniquely toward truly embedded sources and not toward disks. On the other hand hot (T_(ex) ≳ 700 K) H_2, observed primarily through the S(4) line, and [Ne ii] emission is seen mostly in the spatially unresolved component. [Fe ii] and [Si ii] lines are observed in both spatial components. Hot H_(2)O emission is found in the spatially unresolved component of some sources. Conclusions. The observed emission on ≥1000 AU scales is characteristic of PDR emission and likely originates in the outflow cavities in the remnant envelope created by the stellar wind and jets from the embedded young stars. Weak shocks along the outflow wall can also contribute. The compact emission is likely of mixed origin, comprised of optically thick circumstellar disk and/or jet/outflow emission from the protostellar object.

Item Type:Article
Related URLs:
URLURL TypeDescription
van Dishoeck, E. F.0000-0001-7591-1907
Jørgensen, J. K.0000-0001-9133-8047
Blake, G. A.0000-0003-0787-1610
Evans, N. J., II0000-0001-5175-1777
Additional Information:© 2010 ESO. Received 23 December 2009; Accepted 30 April 2010; Published online 06 September 2010. Astrochemistry in Leiden is supported by a NWO Spinoza grant and a NOVA grant. Support for this work, part of the Spitzer Legacy Science Program, was provided by NASA through contract 1224608 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contracts 1407, 1256316, and 1230779.We thank the referee, David Hollenbach, for his thorough and constructive review which helped to improve our paper. All members of the c2d-IRS team are thanked for their feedback; detailed comments from Klaus Pontoppidan are particularly appreciated. We thank the Lorentz Center in Leiden for hosting several meetings that contributed to this paper. Lars Kristensen and Tim van Kempen helped to identify the evolutionary stages of some sources.
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
Subject Keywords:stars: formation; stars: low-mass; stars: protostars; ISM: jets and outflows; ISM: lines and bands; photon-dominated region (PDR)
Record Number:CaltechAUTHORS:20101117-104222858
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Official Citation:c2d Spitzer IRS spectra of embedded low-mass young stars: gas-phase emission lines F. Lahuis, E. F. van Dishoeck, J. K. Jørgensen, G. A. Blake and N. J. Evans A&A 519 A3 (2010) DOI: 10.1051/0004-6361/200913957
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20855
Deposited By: Jason Perez
Deposited On:17 Nov 2010 21:13
Last Modified:09 Mar 2020 13:18

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