Gas-phase CO depletion and N2H+ abundances in starless cores

N. Lippok, R. Launhardt, D. Semenov, A. M. Stutz, Z. Balog, Th Henning, O. Krause, H. Linz, M. Nielbock, Ya N. Pavlyuchenkov, M. Schmalzl, A. Schmiedeke, John H Bieging

Research output: Contribution to journalArticle

26 Citations (Scopus)

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 12CO (2-1), 13CO (2-1), C18O (2-1) and N 2H+ (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 × 105 cm-3. At about this density, the cores typically have the highest relative abundance of N 2H+. 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) × 10 5 yr for 13CO, (6 ± 3) × 104 yr for C18O, and (9 ± 2) × 104 yr for N 2H+. 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 N 2H+. The chemical ages indicate a core lifetime of less than 1 Myr.

Original languageEnglish (US)
Article numberA41
JournalAstronomy and Astrophysics
Volume560
DOIs
StatePublished - Dec 2013

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depletion
vapor phases
dust
gas
hydrogen
temperature
molecular clouds
modeling
ray tracing
profiles
chemical
chemical process
continuums
radiative transfer
relative abundance
chemical evolution
gas temperature
ice
star formation
nitrogen

Keywords

  • Astrochemistry
  • Infrared: ISM
  • ISM: abundances
  • Stars: formation
  • Stars: low-mass
  • Submillimeter: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Lippok, N., Launhardt, R., Semenov, D., Stutz, A. M., Balog, Z., Henning, T., ... Bieging, J. H. (2013). Gas-phase CO depletion and N2H+ abundances in starless cores. Astronomy and Astrophysics, 560, [A41]. https://doi.org/10.1051/0004-6361/201322129

Gas-phase CO depletion and N2H+ abundances in starless cores. / 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.; Bieging, John H.

In: Astronomy and Astrophysics, Vol. 560, A41, 12.2013.

Research output: Contribution to journalArticle

Lippok, N, Launhardt, R, Semenov, D, Stutz, AM, Balog, Z, Henning, T, Krause, O, Linz, H, Nielbock, M, Pavlyuchenkov, YN, Schmalzl, M, Schmiedeke, A & Bieging, JH 2013, 'Gas-phase CO depletion and N2H+ abundances in starless cores', Astronomy and Astrophysics, vol. 560, A41. https://doi.org/10.1051/0004-6361/201322129
Lippok N, Launhardt R, Semenov D, Stutz AM, Balog Z, Henning T et al. Gas-phase CO depletion and N2H+ abundances in starless cores. Astronomy and Astrophysics. 2013 Dec;560. A41. https://doi.org/10.1051/0004-6361/201322129
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. ; Bieging, John H. / Gas-phase CO depletion and N2H+ abundances in starless cores. In: Astronomy and Astrophysics. 2013 ; Vol. 560.
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title = "Gas-phase CO depletion and N2H+ abundances in starless cores",
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 12CO (2-1), 13CO (2-1), C18O (2-1) and N 2H+ (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 × 105 cm-3. At about this density, the cores typically have the highest relative abundance of N 2H+. 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) × 10 5 yr for 13CO, (6 ± 3) × 104 yr for C18O, and (9 ± 2) × 104 yr for N 2H+. 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 N 2H+. The chemical ages indicate a core lifetime of less than 1 Myr.",
keywords = "Astrochemistry, Infrared: ISM, ISM: abundances, Stars: formation, Stars: low-mass, Submillimeter: ISM",
author = "N. Lippok and R. Launhardt and D. Semenov and Stutz, {A. M.} and Z. Balog and Th Henning and O. Krause and H. Linz and M. Nielbock and Pavlyuchenkov, {Ya N.} and M. Schmalzl and A. Schmiedeke and Bieging, {John H}",
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T1 - Gas-phase CO depletion and N2H+ abundances in starless cores

AU - Lippok, N.

AU - Launhardt, R.

AU - Semenov, D.

AU - Stutz, A. M.

AU - Balog, Z.

AU - Henning, Th

AU - Krause, O.

AU - Linz, H.

AU - Nielbock, M.

AU - Pavlyuchenkov, Ya N.

AU - Schmalzl, M.

AU - Schmiedeke, A.

AU - Bieging, John H

PY - 2013/12

Y1 - 2013/12

N2 - 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 12CO (2-1), 13CO (2-1), C18O (2-1) and N 2H+ (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 × 105 cm-3. At about this density, the cores typically have the highest relative abundance of N 2H+. 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) × 10 5 yr for 13CO, (6 ± 3) × 104 yr for C18O, and (9 ± 2) × 104 yr for N 2H+. 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 N 2H+. The chemical ages indicate a core lifetime of less than 1 Myr.

AB - 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 12CO (2-1), 13CO (2-1), C18O (2-1) and N 2H+ (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 × 105 cm-3. At about this density, the cores typically have the highest relative abundance of N 2H+. 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) × 10 5 yr for 13CO, (6 ± 3) × 104 yr for C18O, and (9 ± 2) × 104 yr for N 2H+. 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 N 2H+. The chemical ages indicate a core lifetime of less than 1 Myr.

KW - Astrochemistry

KW - Infrared: ISM

KW - ISM: abundances

KW - Stars: formation

KW - Stars: low-mass

KW - Submillimeter: ISM

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