Complete depletion in prestellar cores

By C. Walmsley, D. Flower, G. P. D. Forêts. 2004

196 citations recorded by the source corpus.

We have carried out calculations of ionization equilibrium and deuterium fractionation for conditions appropriate to a completely depleted, low mass pre-protostellar core, where heavy elements such as C, N, and O have vanished from the gas phase and are incorporated in ice mantles frozen on dust grain surfaces. We put particular emphasis on the interpretation of recent observations of H 2 D +  towards the centre of the prestellar core L 1544 (Caselli et al. [CITE]) and also compute the ambipolar diffusion timescale. We consider explicitly the ortho and para forms of H 2 , H$_{3}^{+}$, and H 2 D + . Our results show that the ionization degree under such conditions depends sensitively on the grain size distribution or, more precisely, on the mean grain surface area per hydrogen nucleus. Depending upon this parameter and upon density, the major ion may be H + , H$_{3}^{+}$, or D$_{3}^{+}$. We show that the abundance of ortho-H 2 D +  observed towards L 1544 can be explained satisfactorily in terms of a complete depletion model and that this species is, as a consequence, an important tracer of the kinematics of prestellar cores.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/2639b1a648461a814c77c85d09e39ba37c0ea775

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. P. Caselli
2. E. Bergin
3. M. Tafalla
4. E. Herbst
5. Cecilia Ceccarelli
6. S. Glover
7. K. Oberg
8. R. Garrod

In Atmospheric Science

1. E. Bergin
2. P. Caselli
3. E. Herbst
4. M. Tafalla
5. K. Oberg
6. Cecilia Ceccarelli
7. H. Roberts
8. S. Glover

In Atomic and Molecular Physics, and Optics

1. E. Bergin
2. M. Tafalla
3. P. Caselli
4. Cecilia Ceccarelli
5. G. P. D. Forêts
6. E. Herbst
7. K. Oberg
8. T. Millar

Citations in the corpus

• The UMIST database for astrochemistry 2012 (2012, background): “We also include, for download, a set of state-specific deuterated reactions involving isotopologues of H2, H + 2 , and H + 3 , mostly taken from Flower et al. (2004), Walmsley et al. (2004) and Hugo et al. (2009).”
• The chemistry of multiply deuterated species in cold, dense interstellar cores (2004, background): “Walmsley et al. (2004). species have more product channels than their un-deuterated analogues, we have assumed statistical branching ratios (Millar et al. 1989), except for the cases where experimental measurements indicate otherwise; e.g., for the recombination of the deuterated isotopomers of…”
• Uncertainties in H2 and HD chemistry and cooling and their role in early structure formation (2008, background): “…Dalgarno & McDowell (1956), scaled by D reduced mass; (35) same as corresponding H reaction, with branching ratio assumed uniform; (36) Xu & Fabrikant (2001); (37) estimate; (38) Walmsley et al. (2004); (39) fit based on cross-section from Wang & Stancil (2002); (40) Trevisan & Tennyson (2002b).”
• Competition between CO and N2 Desorption from Interstellar Ices (2005, background): “However, as cores evolve toward the collapse phase, densities increase and the timescales for volatile gas-phase molecules to deplete onto grains become shorter than the age of the core (e.g., Caselli et al. 1999; Walmsley et al. 2004).”
• Molecular Evolution in Collapsing Prestellar Cores. III. Contraction of a Bonnor-Ebert Sphere (2004, unknown): “2002; Walmsley et al. 2004), this process is not included in our model.”
• Cold Dark Clouds: The Initial Conditions for Star Formation (2007, methodology): “The effects of freeze-out can alter both the pre-factor and the exponent of the density dependence (Bergin & Langer 1997; Caselli et al. 2002c; Walmsley et al. 2004), but see also Ciolek & Mouschovias (1998).”
• Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio (2008, background): “Different values could be advocated (for example, in places where depletion is important, the ices increase the dust mass by up to 25%, Walmsley et al. 2004) but the net result is to change only slightly the average grain size which is not well constrained in the PSCs in any case.”
• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse (2006, methodology): “…have confirmed , that the abundances of the singly and multiply deuterated forms of H + 3 can attain exceptionally high values under conditions of extreme heavy element depletion (Caselli et al. 2003, Ceccarelli et al. 2004, Vastel et al. 2004; Walmsley et al. 2004, Ceccarelli & Dominik 2005).”
• Probing the Evolutionary Status of Starless Cores through N2H+ and N2D+ Observations (2004, background): “…Hþ3 , without any distinction between the ortho and para forms of molecular hydrogen and H2D + and without taking into account the so-called backreactions between, e.g., ortho-H2 and ortho-H2D + (Gerlich et al. 2002), which limit the deuterium fractionation, as discussed in Walmsley et al. (2004).”