Molecular Evolution in Collapsing Prestellar Cores. III. Contraction of a Bonnor-Ebert Sphere

By Y. Aikawa, E. Herbst, H. Roberts, P. Caselli. 2004

174 citations recorded by the source corpus.

The gravitational collapse of a spherical cloud core is investigated by numerical calculations. The initial conditions of the core lie close to the critical Bonnor-Ebert sphere with a central density of ~104 cm-3 in one model (α = 1.1), while gravity overwhelms pressure in the other (α = 4.0), where α is the internal gravity-to-pressure ratio. The α = 1.1 model shows reasonable agreement with the observed velocity field in prestellar cores. Molecular distributions in cores are calculated by solving a chemical reaction network that includes both gas-phase and grain-surface reactions. When the central density of the core reaches 105 cm-3, carbon-bearing species are significantly depleted in the central region of the α = 1.1 model, while the depletion is only marginal in the other model. The two different approaches encompass the observed variations of molecular distributions in different prestellar cores, suggesting that molecular distributions can be probes of contraction or accumulation timescales of cores. The central enhancement of the NH3/N2H+ ratio, which is observed in some prestellar cores, can be reproduced under certain conditions by adopting recently measured branching fractions for N2H+ recombination. Various molecular species, such as CH3OH and CO2, are produced by grain-surface reactions. The ice composition depends sensitively on the assumed temperature. Multideuterated species are included in our most recent gas-grain chemical network. The deuterated isotopomers of H are useful as probes of the central regions of evolved cores, in which gas-phase species with heavy elements are strongly depleted. At 10 K, our model can reproduce the observed abundance ratio of ND3/NH3 but underestimates the isotopic ratios of deuterated to normal methanol.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/041beabcfe4fb6447dd8080579da0ecf0b127541

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In Astronomy and Astrophysics

1. P. Caselli
2. Ralf Klessen
3. R. Garrod
4. E. Bergin
5. E. Dishoeck
6. E. Herbst
7. Cecilia Ceccarelli
8. M. Tafalla

In Atmospheric Science

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

Citations in the corpus

• Dense core formation by fragmentation of velocity-coherent filaments in L1517 (2011, background): “Observationally, SO is known to be highly sensitive to molecular freeze out (Tafalla et al. 2006), and in addition, it is predicted to decrease in abundance with time (Bergin & Langer 1997; Aikawa et al. 2005).”
• MODELING COLLAPSE AND ACCRETION IN TURBULENT GAS CLOUDS: IMPLEMENTATION AND COMPARISON OF SINK PARTICLES IN AMR AND SPH (2010, background): “Collapse of a Bonnor-Ebert Sphere The collapse of supercritical Bonnor-Ebert spheres (Ebert 1955; Bonnor 1956), is a well-studied problem (e.g. Larson 1969; Foster & Chevalier 1993; Banerjee et al. 2004; Aikawa et al. 2005), and thus represents a good test case for our sink particle implementation.”
• Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results (2010, methodology): “The sensitivity limits are based on H2O column densities estimated using the model results of Aikawa et al. (2005) for chemically “old” sources like L1544.”
• Desorption rates and sticking coefficients for CO and N2 interstellar ices (2006, background): “1) suggests that the N2 abundance is always less than or equal to that of CO. Models including gas-grain chemistry predict N2 ice abundances that are typically a factor 5−20 lower than those of CO ice (Hasegawa & Herbst 1993; Shalabiea & Greenberg 1994; Bergin et al. 1995; Aikawa et al. 2005).”
• WATER, O2, AND ICE IN MOLECULAR CLOUDS (2008, background): “For example, in our standard model, integrating to AV = 10, the O not in refractory grains is divided 56% H2O-ice, 25% gas-phase O, 10% CO-ice, and 8% gasphase CO.”
• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores (2007, methodology): “…however, it is more convenient to follow the Lagrangian approach, in which we consider the temporal variation of physical parameters in assorted collapsing shells, because this temporal variation represents the conditions in which the chemical reaction network is solved (Aikawa et al. 2001, 2005).”
• Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “NH3 then forms from N2H + (Geppert et al. 2004; Aikawa et al. 2005).”
• Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio (2008, background): “This can be explained by the fact that N2H+ is mainly destroyed by CO (Caselli 2002, Pagani et al. 2005, Aikawa et al. 2005), so that the CO freezeout implies a drop in the destruction rate of N2H+.”
• On the internal structure of starless cores II. A molecular survey of L1498 and L1517B (2006, methodology): “Very recently, (Aikawa et al. 2005, AHRC05 hereafter) have presented the most up-todate chemical model of starless core contraction.”
• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores (2006, methodology): “Additionally, we modify the rates of hydrogen reactions that have activation energy barriers, following the method of Aikawa et al. (2005).”
• Observing the gas temperature drop in the high-density nucleus of L 1544 (2007, background): “Large deuterium enrichment is a characteristic of the high density nuclei of pre-stellar cores and it is a useful test of our understanding of the chemistry (e.g. Aikawa et al. 2005; Flower et al. 2006) to measure the [NH2D]/[NH3] ratio at high angular resolution.”