Universität zu Köln

Lippok, N., Launhardt, R., Semenov, D., Stutz, A. M., Balog, Z., Henning, Th, Krause, O., Linz, H., Nielbock, M., Pavlyuchenkov, Ya N., Schmalzl, M., Schmiedeke, A. and Bieging, J. H. (2013). Gas-phase CO depletion and N2H+ abundances in starless cores. Astron. Astrophys., 560. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. In the dense and cold interiors of starless molecular cloud cores, a number of chemical processes allow for the formation of complex molecules and the deposition of ice layers on dust grains. Dust density and temperature maps of starless cores derived from Herschel continuum observations constrain the physical structure of the cloud cores better than ever before. We use these to model the temporal chemical evolution of starless cores. Aims. We derive molecular abundance profiles for a sample of starless cores. We then analyze these using chemical modeling based on dust temperature and hydrogen density maps derived from Herschel continuum observations. Methods. We observed the (CO)-C-12(2-1), (CO)-C-13(2-1), (CO)-O-18(2-1) and N2H+ (1-0) transitions towards seven isolated, nearby low-mass starless molecular cloud cores. Using far infrared (FIR) and submillimeter (submm) dust emission maps from the Herschel key program Earliest Phases of Star formation (EPoS) and by applying a ray-tracing technique, we derived the physical structure (density, dust temperature) of these cores. Based on these results we applied time-dependent chemical modeling of the molecular abundances. We modeled the molecular emission profiles with a line-radiative transfer code and compared them to the observed emission profiles. Results. CO is frozen onto the grains in the center of all cores in our sample. The level of CO depletion increases with hydrogen density and ranges from 46% up to more than 95% in the core centers of the three cores with the highest hydrogen density. The average hydrogen density at which 50% of CO is frozen onto the grains is 1.1 +/- 0.4 x 10(5) cm(-3). At about this density, the cores typically have the highest relative abundance of N2H+. The cores with higher central densities show depletion of N2H+ at levels of 13% to 55%. The chemical ages for the individual species are on average (2 +/- 1) x 10(5) yr for (CO)-C-13 (6 +/- 3) x 10(4) yr for (CO)-O-18, and (9 +/- 2) x 10(4) yr for N2H+. Chemical modeling indirectly suggests that the gas and dust temperatures decouple in the envelopes and that the dust grains are not yet significantly coagulated. Conclusions. We observationally confirm chemical models of CO-freezeout and nitrogen chemistry. We find clear correlations between the hydrogen density and CO depletion and the emergence of N2H+. The chemical ages indicate a core lifetime of less than 1 Myr.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Lippok, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Launhardt, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Semenov, D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutz, A. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Balog, Z. UNSPECIFIED UNSPECIFIED UNSPECIFIED Henning, Th UNSPECIFIED UNSPECIFIED UNSPECIFIED Krause, O. UNSPECIFIED UNSPECIFIED UNSPECIFIED Linz, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Nielbock, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pavlyuchenkov, Ya N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schmalzl, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schmiedeke, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bieging, J. H. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-470533
DOI:	10.1051/0004-6361/201322129
Journal or Publication Title:	Astron. Astrophys.
Volume:	560
Date:	2013
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language (CO)-O-18 DEPLETION; TURBULENT-DIFFUSION; INTERNAL STRUCTURE; THERMAL STRUCTURE; DUST-TEMPERATURE; EARLIEST PHASES; PRESTELLAR CORE; FORMATION EPOS; HERSCHEL; CLOUD Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/47053