Effect of ambipolar diffusion on ion abundances in contracting protostellar cores

Glenn E. Ciolek, Telemachos Ch Mouschovias

Research output: Contribution to journalArticle

Abstract

Numerical simulations and analytical solutions have established that ambipolar diffusion can reduce the dust-to-gas ratio in magnetically and thermally supercritical cores during the epoch of core formation. We study the effect that this has on the ion chemistry in contracting protostellar cores and present a simplified analytical method that allows one to calculate the ion power-law exponent k (=d ln nid ln an, where H, and nn are the ion and neutral densities, respectively) as a function of core density. We find that, as in earlier numerical simulations, no single value of k can adequately describe the ion abundance for nn ≲ 109 cm-3, a result that is contrary to the "canonical" value of k = found in previous static equilibrium chemistry calculations and often used to study the effect of ambipolar diffusion in interstellar clouds. For typical cloud and grain parameters, reduction of the abundance of grains results in k > 1/2 during the core formation epoch (densities ; 105 cm-3). As a consequence, observations of the degree of ionization in cores could be used, in principle, to determine whether ambipolar diffusion is responsible for core formation in interstellar molecular clouds. For densities ≫ 105 cm-3, k is generally 1/2.

Original languageEnglish (US)
Pages (from-to)280-289
Number of pages10
JournalAstrophysical Journal
Volume504
Issue number1 PART I
DOIs
StatePublished - Jan 1 1998

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ambipolar diffusion
ion
ions
simulation
analytical method
time measurement
power law
ionization
chemistry
dust
effect
molecular clouds
gas
exponents
gases

Keywords

  • Diffusion
  • Dust, extinction
  • ISM: abundances
  • ISM: magnetic fields
  • MHD

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Effect of ambipolar diffusion on ion abundances in contracting protostellar cores. / Ciolek, Glenn E.; Mouschovias, Telemachos Ch.

In: Astrophysical Journal, Vol. 504, No. 1 PART I, 01.01.1998, p. 280-289.

Research output: Contribution to journalArticle

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AB - Numerical simulations and analytical solutions have established that ambipolar diffusion can reduce the dust-to-gas ratio in magnetically and thermally supercritical cores during the epoch of core formation. We study the effect that this has on the ion chemistry in contracting protostellar cores and present a simplified analytical method that allows one to calculate the ion power-law exponent k (=d ln nid ln an, where H, and nn are the ion and neutral densities, respectively) as a function of core density. We find that, as in earlier numerical simulations, no single value of k can adequately describe the ion abundance for nn ≲ 109 cm-3, a result that is contrary to the "canonical" value of k = found in previous static equilibrium chemistry calculations and often used to study the effect of ambipolar diffusion in interstellar clouds. For typical cloud and grain parameters, reduction of the abundance of grains results in k > 1/2 during the core formation epoch (densities ; 105 cm-3). As a consequence, observations of the degree of ionization in cores could be used, in principle, to determine whether ambipolar diffusion is responsible for core formation in interstellar molecular clouds. For densities ≫ 105 cm-3, k is generally 1/2.

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