HD depletion in starless cores

Abstract

Aims: We aim to investigate the abundances of light deuterium-bearing species such as HD, H2D+ and D2H+ in a gas-grain chemical model including an extensive description of deuterium and spin state chemistry, in physical conditions appropriate to the very centers of starless cores. Methods: We combine a gas-grain chemical model with radiative transfer calculations to simulate density and temperature structure in starless cores. The chemical model includes deuterated forms of species with up to 4 atoms and the spin states of the light species H2, H2+ and H3+ and their deuterated forms. Results: We find that HD eventually depletes from the gas phase because deuterium is efficiently incorporated to grain-surface HDO, resulting in inefficient HD production on grains. HD depletion has consequences not only on the abundances of e.g. H2D+ and D2H+, whose production depends on the abundance of HD, but also on the spin state abundance ratios of the various light species, when compared with the complete depletion model where heavy elements do not influence the chemistry. Conclusions: While the eventual HD depletion leads to the disappearance of light deuterium-bearing species from the gas phase in a relatively short timescale at high density, we find that at late stages of core evolution the abundances of H2D+ and D2H+ increase toward the core edge and the disributions become extended. The HD depletion timescale increases if less oxygen is initially present in the gas phase, owing to chemical interaction between the gas and the dust predecing the starless core phase. Our results are greatly affected if H2 is allowed to tunnel on grain surfaces, and therefore more experimental data not only on tunneling but also on the O + H2 surface reaction in particular is needed.

14 pages, 12 figures, abstract abridged; accepted for publication in A & A

References in corpus (10)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
• Water Formation through a Quantum Tunneling Surface Reaction, OH + H2, at 10 K
• The Distribution of Ortho-H_2D+(1_1,0 - 1_1,1) in L1544: Tracing the Deuteration Factory in Prestellar Cores
• Water ice deuteration: a tracer of the chemical history of protostars
• HD and H2 formation in low-metallicity dusty gas clouds at high redshift
• Warm water deuterium fractionation in IRAS 16293-2422 - The high-resolution ALMA and SMA view
• Hot water in the inner 100 AU of the Class 0 protostar NGC1333 IRAS2A
• Water deuterium fractionation in the inner regions of two solar type protostars

Cited by in corpus (42)

• Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores
• Interstellar chemistry of nitrogen hydrides in dark clouds
• Deuterated methanol in the pre-stellar core L1544
• Chemo-dynamical deuterium fractionation in the early solar nebula: The origin of water on Earth and in asteroids and comets
• Benchmarking spin-state chemistry in starless core models
• Water deuteration and ortho-to-para nuclear spin ratio of H2 in molecular clouds formed via the accumulation of HI gas
• The Deuterium Fractionation Timescale in Dense Cloud Cores: A Parameter Space Exploration
• Chemistry in Disks. IX. Observations and modeling of HCO+ and DCO+ in DM Tau
• Chemistry and Radiative Transfer of Water in Cold, Dense Clouds
• Spin-state chemistry of deuterated ammonia
• The Deuterium Fraction in Massive Starless Cores and Dynamical Implications
• Why does ammonia not freeze out in the center of pre-stellar cores?
• Revealing H2D+ depletion and compact structure in starless and protostellar cores with ALMA
• Carbon isotopic fractionation in molecular clouds
• Deuteration of ammonia in the starless core Ophiuchus/H-MM1
• Chemical modeling of water deuteration in IRAS16293-2422
• Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data
• The core population and kinematics of a massive clump at early stages: an ALMA view
• Multiple paths of deuterium fractionation in protoplanetary disks
• Widespread deuteration across the IRDC G035.39-00.33
• First Time-dependent Study of H2 and H3+ Ortho-Para Chemistry in the Diffuse Interstellar Medium: Observations Meet Theoretical Predictions
• Identification of prestellar cores in high-mass star forming clumps via ${\mathrm{H}}_2{\mathrm{D}}^{+}$ observations with ALMA
• Hydrogen isotope exchanges between water and methanol in interstellar ices
• ALMA detections of the youngest protostars in Ophiuchus
• On the size of the CO-depletion radius in the IRDC G351.77-0.51
• Deuterium fractionation and H2D+ evolution in turbulent and magnetized cloud cores
• Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration
• Experimental and theoretical studies of D + H${}_3^{+}$ $\to$ H${}_2$D${}^{+}$ + H
• The D/H Ratio of Water Ice at Low Temperatures
• The effect of multilayer ice chemistry on gas-phase deuteration in starless cores
• On the stability of non-isothermal Bonnor-Ebert spheres. II. The effect of gas temperature on the stability
• Using HCO${}^{+}$ isotopologues as tracers of gas depletion in protoplanetary disk gaps
• The first frost in the Pipe Nebula
• Deuterium Chemodynamics of Massive Pre-Stellar Cores
• The HIFI spectral survey of AFGL 2591 (CHESS). III. Chemical structure of the protostellar envelope
• Digging into the Interior of Hot Cores with ALMA (DIHCA). V. Deuterium Fractionation of Methanol
• Detectability of deuterated water in prestellar cores
• Chemical exploration of Galactic cold cores
• A low cosmic-ray ionisation rate in the prestellar core Ophiuchus/H-MM1. Mapping of the molecular ions ortho-H2D+, N2H+, and DCO+
• Deuterated forms of H${}_3^{+}$ and their importance in astrochemistry
• Deuterium fractionation and CO depletion in Barnard 5
• Synthetic observations using POLARIS: an application to simulations of massive prestellar cores