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The nature of the Class I population in Ophiuchus as revealed through gas and dust mapping

van Kempen, T. A. and van Dishoeck, E. F. and Salter, D. M. and Hogerheijde, M. R. and Jørgensen, J. K. and Boogert, A. C. A. (2009) The nature of the Class I population in Ophiuchus as revealed through gas and dust mapping. Astronomy and Astrophysics, 498 (1). pp. 167-194. ISSN 0004-6361.

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Context. The Ophiuchus clouds, in particular L 1688, are an excellent region to study the embedded phases Context. The Ophiuchus clouds, in particular L 1688, are an excellent region to study the embedded phases of star formation, due to the relatively large number of protostars. However, the standard method of finding and characterizing embedded young stellar objects (YSOs) through just their infrared spectral slope does not yield a reliable sample. This may affect the age determinations, often derived from the statistics on the total number of embedded YSOs and pre-main sequence stars within a cloud. Aims. Our aim is to characterize the structure of protostellar envelopes on an individual basis and to correctly identify the embedded YSO population of L 1688. Methods. Spectral maps of the HCO^+ J = 4−3 and C^(18)O J = 3−2 lines, using the HARP-B array on the James Clerk Maxwell Telescope and SCUBA 850 μm dust maps, are obtained of all sources in the L 1688 region with infrared spectral slopes consistent with, or close to, that of embedded YSOs. Selected 350 μm maps obtained with the Caltech Submillimeter Observatory are presented as well. The properties, extent and variation of dense gas, column density and dust up to 1’ (∼7500 AU) are probed at 15” resolution. Using the spatial variation of the gas and dust, together with the intensity of the HCO+ J = 4−3 line, we are able to accurately identify the truly embedded YSOs and determine their properties. Results. The protostellar envelopes range from 0.05 to 0.5 M_ ⊙ in mass. The concentration of HCO+ emission (∼0.5 to 0.9) is generally higher than that of the dust concentration. Combined with absolute intensities, HCO^+ proves to be a better tracer of protostellar envelopes than dust, which can contain disk and cloud contributions. Our total sample of 45 sources, including all previously classified Class I sources, several flat-spectrum sources and some known disks, was re-classified using the molecular emission. Of these, only 17 sources are definitely embedded YSOs. Four of these embedded YSOs have little (0.1−0.2 M_⊙) envelope material remaining and are likely at the interesting transitional stage from embedded YSO to T Tauri star. About half of the flat-spectrum sources are found to be embedded YSOs and about half are disks. Conclusions. The presented classification method is successful in separating embedded YSOs from edge-on disks and confused sources. The total embedded population of the Ophiuchus L 1688 cloud is found almost exclusively in Oph-A, Oph-B2 and the Ophiuchus ridge with only three embedded YSOs not related to these regions. The detailed characterization presented will be necessary to interpret deep interferometric ALMA and future Herschel observations.

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van Dishoeck, E. F.0000-0001-7591-1907
Jørgensen, J. K.0000-0001-9133-8047
Additional Information:Received 23 June 2008 / Accepted 22 February 2009. TvK and astrochemistry at Leiden Observatory are supported by a Spinoza prize and by NWO grant 614.041.004. Remo Tilanus and Jan Wouterloot are thanked for the extensive support on the observing and reduction of HARP-B data and Arno Kockx for carrying out a large part of the HARP-B observations. The support from the APEX and MPIfR staff on the APEX2a data is greatly appreciated. The assistance on the usage of the COMPLETE data from Doug Johnstone and Helen Kirk is recognized. The authors are grateful to the c2d team, especially Mike Dunham (general), Luisa Rebull (MIPS) and Fred Lahuis (IRS), for their help on the Spitzer data and useful discussion.
Funding AgencyGrant Number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)614.041.004
Subject Keywords:astrochemistry; circumstellar matter; stars: formation; submillimeter; ISM: clouds; ISM: molecules
Issue or Number:1
Record Number:CaltechAUTHORS:20090911-145124889
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Official Citation: The nature of the Class I population in Ophiuchus as revealed through gas and dust mapping T. A. van Kempen, E. F. van Dishoeck, D. M. Salter, M. R. Hogerheijde, J. K. Jørgensen and A. C. A. Boogert A&A 498 (1) 167-194 (2009) DOI: 10.1051/0004-6361/200810445
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15781
Deposited By: Tony Diaz
Deposited On:15 Sep 2009 15:47
Last Modified:09 Mar 2020 13:18

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