Molecular Evolution in Collapsing Prestellar Cores

By Y. Aikawa, N. Ohashi, S. Inutsuka, E. Herbst, S. Takakuwa. 2001

195 citations recorded by the source corpus.

We have investigated the evolution and distribution of molecules in collapsing prestellar cores via numerical chemical models, adopting the Larson-Penston solution and its delayed analogs to study collapse. Molecular abundances and distributions in a collapsing core are determined by the balance among the dynamical, chemical, and adsorption timescales. When the central density nH of a prestellar core with the Larson-Penston flow rises to 3 × 106 cm-3, the CCS and CO column densities are calculated to show central holes of radius 7000 and 4000 AU, respectively, while the column density of N2H+ is centrally peaked. These predictions are consistent with observations of L1544. If the dynamical timescale of the core is larger than that of the Larson-Penston solution owing to magnetic fields, rotation, or turbulence, the column densities of CO and CCS are smaller, and their holes are larger than in the Larson-Penston core with the same central gas density. On the other hand, N2H+ and NH3 are more abundant in the more slowly collapsing core. Therefore, molecular distributions can probe the collapse timescale of prestellar cores. Deuterium fractionation has also been studied via numerical calculations. The deuterium fraction in molecules increases as a core evolves and molecular depletion onto grains proceeds. When the central density of the core is nH = 3 × 106 cm-3, the ratio DCO+/HCO+ at the center is in the range 0.06-0.27, depending on the collapse timescale and adsorption energy; this range is in reasonable agreement with the observed value in L1544.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/314513ace6f42a876d3f8fcf389f6799e66f84f8

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. M. Tafalla
3. E. Herbst
4. E. Bergin
5. P. Myers
6. R. Garrod
7. Ralf Klessen
8. V. Wakelam

In Atmospheric Science

1. P. Caselli
2. E. Herbst
3. M. Tafalla
4. E. Bergin
5. R. Garrod
6. V. Wakelam
7. Ralf Klessen
8. H. Roberts

Citations in the corpus

• Dense Cores in Dark Clouds. XIV. N2H+ (1-0) Maps of Dense Cloud Cores (2002, background): “1998, ApJ, 496, L109 Myers, P. C., & Benson, P. J. 1983, ApJ, 266, 309 Myers, P. C., Fuller, G. A., Goodman, A. A., & Benson, P. J. 1991, ApJ, 376, 561 Park, Y.-S., Panis, J.-F., Ohashi, N., Choi, M., & Minh, Y. C. 2000, ApJ, 542, 344 Pratap, P., Dickens, J. E., Snell, R. L.,Miralles,M. P., Bergin, ”
• Molecular Ions in L1544. II. The Ionization Degree (2001, methodology): “It is relevant in this contest that the detailed gas–grain chemical–dynamical model of L1544, presented by Aikawa et al. 2001 (which includes depletion onto dust grains but no surface processing of accreted species) predicts large O fractions across the core (from ∼ 10 −4 at n(H 2 ) ∼ 10 5 cm −3 to…”
• Evolution of Chemistry and Molecular Line Profiles during Protostellar Collapse (2004, background): “Several theoretical studies (Bergin & Langer 1997; Aikawa et al. 2001; Caselli et al. 2002; Li et al. 2002; Shematovich et al. 2003; Aikawa et al. 2003) examined the chemistry in preprotostellar cores (PPCs).”
• The Nature and Distribution of the Organic Material in Carbonaceous Chondrites and Interplanetary Dust Particles (2006, background): “…by spectroscopic observation of young stellar objects (e.g., Qi et al., 2003) and theoretical models of collapsing interstellar cores (e.g., Aikawa et al., 2003), protoplanetary disks (e.g., Aikawa et al., 2002), and planetesimal mass distribution (e.g., Kortenkamp et al., 2001) that could…”
• Molecular Evolution in Collapsing Prestellar Cores. III. Contraction of a Bonnor-Ebert Sphere (2004, methodology): “Because of the low adsorption energy of their precursor molecule N2 on grain surfaces, the depletion of NH3 and N2H + is less significant than that for other heavy-element species (Bergin & Langer 1997; Aikawa et al. 2001, 2003).”
• Condensation of Rocky Material in Astrophysical Environments (2023, background): “Network calculations appear to be most effective for low-temperature phase relations, and gas-phase reactions in the H-C-N-O-S system (e.g., Hasegawa and Herbst, 1993; Bettens and Herbst, 1995; Gail, 1998; Aikawa et al., 2003; Semenov et al., 2004).”
• The H2O Southern Galactic Plane Survey (HOPS) – I. Techniques and H2O maser data (2011, background): “On the other hand, NH3 appears to be more robust than CO, CS or HCO+ against freeze-out on to dust grains (e.g. Aikawa et al. 2001).”
• Enhanced Deuterium Fractionation in Dense Interstellar Cores Resulting from Multiply Deuterated H3+ (2003, background): “It is more likely that the assumption of constant physical conditions is unrealistic: the DCO emission from L1544, for example, may well be coming from a lower density region, so a much more complex model, such as that of Aikawa et al. (2001, 2003), is required.”
• On the internal structure of starless cores II. A molecular survey of L1498 and L1517B (2006, methodology): “…al. (2006), however, show that the two binding energies differ by less than 10%, and this may seem insufficient to account for the different depletion behavior of CO and N2H+ (note however that Aikawa et al. 2001 find differential depletion even when using similar binding energies for CO and N2).”
• Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “In contrast, the N2H + and NH3 emission in L1544 when observed in high resolution appears to coincide with the continuum emission peak (Williams et al. 1999, Crapsi et al. 2006, in prep.).”
• On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B (2004, unknown): “…modeled in detail by a number of authors over the last few years (Bergin & Langer 1997; Charnley 1997; Caselli et al. 1999; Nejad & Wagenblast 1999; Aikawa et al. 2001, 2003; Li et al. 2002; Shematovich et al. 2003), and their results are in general agreement with the observations and analysis…”
• Probing the Evolutionary Status of Starless Cores through N2H+ and N2D+ Observations (2004, background): “Several authors have investigated the chemical structure of prestellar cores, coupling together dynamical and chemical evolution with detailed models (Bergin & Langer 1997; Aikawa et al. 2001; Li et al. 2002; Shematovich et al. 2003).”
• Systematic Molecular Differentiation in Starless Cores (2001, background): “Still, the reasonable success of the BL97 model (and those by Aikawa et al. 2001 and Caselli et al. 2002c) shows that most, or all, the chemical differentiation we have observed in starless cores very likely arises from depletion and reactions triggered by depletion.”
• Control of star formation by supersonic turbulence (2000, background): “…of multi-molecule observations of cloud cores with time-dependent chemical models indicates typical ages of about 105 years (e.g. Bergin & Langer 1997, Pratap et al. 1997, Aikawa et al. 2001; or see the reviews by van Dishoeck et al. 1993, van Dishoeck & Black 1998, and Langer et al. 2000).”
• The chemistry of multiply deuterated species in cold, dense interstellar cores (2004, unknown): “Aikawa et al. (2001, 2003) have also presented models of prestellar cores similar to L1544, in which the dynamics of the cloud collapse are modelled to give the evolution of the density profile over time.”
• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores (2007, methodology): “Theoretical models show that the CO depletion is caused by adsorption onto grains (Bergin & Langer 1997; Aikawa et al. 2001), and that the CO depletion helps to temporarily maintain the N2H + abundance at the core center.”