Magnetic braking, ambipolar diffusion, and the formation of cloud cores and protostars. III. Effect of the initial mass-to-flux ratio

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Abstract

Two previous papers have formulated the problem of the formation and contraction of protostellar cores in isothermal, rotating, self-gravitating, magnetically supported model molecular clouds and have presented results, respectively, for a typical case and for the effects of varying five dimensionless free parameters of the problem. In this paper, we study the effect of varying the sixth parameter μd, c0, the initial central mass-to-flux ratio in units of the critical value for collapse. Clouds with initial central mass-to-flux ratio ranging from highly subcritical (μd, c0 = 0.1) to initially critical (μd, c0 = 1.0) are studied. Core formation is initially quasistatic (i.e., negligible acceleration) for the subcritical clouds but dynamic for the critical cloud. In the case of the critical cloud, magnetic-tension forces bring an end to the magnetic-braking-induced, initial phase of (dynamic) collapse (caused by the rapid loss of rotational support); quasistatic contraction follows. After ambipolar diffusion increases (quasistatically) the central mass-to-flux ratio above the critical value cores in all model clouds enter a dynamic phase of contraction. We find that, by the end of the isothermal phase of contraction, at a central density enhancement of about 106 (e.g., from 3 × 103 cm-3 to 3 × 109 cm-3), the widest range of core masses and angular momenta is obtained from the variation of the free parameter μd, c0; specifically, we find that Mcore ∝ μd, c0, and (J/M)core ∝ μ2d, c0. The observationally guided range of values of μd, c0 in our parameter study can explain naturally a range of core masses 3-30 M and specific angular momenta 1019-1021 cm2 s-1.

Original languageEnglish (US)
Pages (from-to)271-283
Number of pages13
JournalAstrophysical Journal
Volume453
Issue number1
DOIs
StatePublished - Nov 1 1995

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ambipolar diffusion
braking
protostars
contraction
angular momentum
magnetic clouds
molecular clouds
effect
parameter
momentum
augmentation

Keywords

  • Diffusion
  • ISM: clouds
  • ISM: magnetic fields
  • MHD
  • Stars: formation
  • Stars: pre-main-sequence
  • Stars: rotation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "Magnetic braking, ambipolar diffusion, and the formation of cloud cores and protostars. III. Effect of the initial mass-to-flux ratio",
abstract = "Two previous papers have formulated the problem of the formation and contraction of protostellar cores in isothermal, rotating, self-gravitating, magnetically supported model molecular clouds and have presented results, respectively, for a typical case and for the effects of varying five dimensionless free parameters of the problem. In this paper, we study the effect of varying the sixth parameter μd, c0, the initial central mass-to-flux ratio in units of the critical value for collapse. Clouds with initial central mass-to-flux ratio ranging from highly subcritical (μd, c0 = 0.1) to initially critical (μd, c0 = 1.0) are studied. Core formation is initially quasistatic (i.e., negligible acceleration) for the subcritical clouds but dynamic for the critical cloud. In the case of the critical cloud, magnetic-tension forces bring an end to the magnetic-braking-induced, initial phase of (dynamic) collapse (caused by the rapid loss of rotational support); quasistatic contraction follows. After ambipolar diffusion increases (quasistatically) the central mass-to-flux ratio above the critical value cores in all model clouds enter a dynamic phase of contraction. We find that, by the end of the isothermal phase of contraction, at a central density enhancement of about 106 (e.g., from 3 × 103 cm-3 to 3 × 109 cm-3), the widest range of core masses and angular momenta is obtained from the variation of the free parameter μd, c0; specifically, we find that Mcore ∝ μd, c0, and (J/M)core ∝ μ2d, c0. The observationally guided range of values of μd, c0 in our parameter study can explain naturally a range of core masses 3-30 M⊙ and specific angular momenta 1019-1021 cm2 s-1.",
keywords = "Diffusion, ISM: clouds, ISM: magnetic fields, MHD, Stars: formation, Stars: pre-main-sequence, Stars: rotation",
author = "Shantanu Basu and Mouschovias, {Telemachos Ch}",
year = "1995",
month = "11",
day = "1",
doi = "10.1086/176387",
language = "English (US)",
volume = "453",
pages = "271--283",
journal = "Astrophysical Journal",
issn = "0004-637X",
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TY - JOUR

T1 - Magnetic braking, ambipolar diffusion, and the formation of cloud cores and protostars. III. Effect of the initial mass-to-flux ratio

AU - Basu, Shantanu

AU - Mouschovias, Telemachos Ch

PY - 1995/11/1

Y1 - 1995/11/1

N2 - Two previous papers have formulated the problem of the formation and contraction of protostellar cores in isothermal, rotating, self-gravitating, magnetically supported model molecular clouds and have presented results, respectively, for a typical case and for the effects of varying five dimensionless free parameters of the problem. In this paper, we study the effect of varying the sixth parameter μd, c0, the initial central mass-to-flux ratio in units of the critical value for collapse. Clouds with initial central mass-to-flux ratio ranging from highly subcritical (μd, c0 = 0.1) to initially critical (μd, c0 = 1.0) are studied. Core formation is initially quasistatic (i.e., negligible acceleration) for the subcritical clouds but dynamic for the critical cloud. In the case of the critical cloud, magnetic-tension forces bring an end to the magnetic-braking-induced, initial phase of (dynamic) collapse (caused by the rapid loss of rotational support); quasistatic contraction follows. After ambipolar diffusion increases (quasistatically) the central mass-to-flux ratio above the critical value cores in all model clouds enter a dynamic phase of contraction. We find that, by the end of the isothermal phase of contraction, at a central density enhancement of about 106 (e.g., from 3 × 103 cm-3 to 3 × 109 cm-3), the widest range of core masses and angular momenta is obtained from the variation of the free parameter μd, c0; specifically, we find that Mcore ∝ μd, c0, and (J/M)core ∝ μ2d, c0. The observationally guided range of values of μd, c0 in our parameter study can explain naturally a range of core masses 3-30 M⊙ and specific angular momenta 1019-1021 cm2 s-1.

AB - Two previous papers have formulated the problem of the formation and contraction of protostellar cores in isothermal, rotating, self-gravitating, magnetically supported model molecular clouds and have presented results, respectively, for a typical case and for the effects of varying five dimensionless free parameters of the problem. In this paper, we study the effect of varying the sixth parameter μd, c0, the initial central mass-to-flux ratio in units of the critical value for collapse. Clouds with initial central mass-to-flux ratio ranging from highly subcritical (μd, c0 = 0.1) to initially critical (μd, c0 = 1.0) are studied. Core formation is initially quasistatic (i.e., negligible acceleration) for the subcritical clouds but dynamic for the critical cloud. In the case of the critical cloud, magnetic-tension forces bring an end to the magnetic-braking-induced, initial phase of (dynamic) collapse (caused by the rapid loss of rotational support); quasistatic contraction follows. After ambipolar diffusion increases (quasistatically) the central mass-to-flux ratio above the critical value cores in all model clouds enter a dynamic phase of contraction. We find that, by the end of the isothermal phase of contraction, at a central density enhancement of about 106 (e.g., from 3 × 103 cm-3 to 3 × 109 cm-3), the widest range of core masses and angular momenta is obtained from the variation of the free parameter μd, c0; specifically, we find that Mcore ∝ μd, c0, and (J/M)core ∝ μ2d, c0. The observationally guided range of values of μd, c0 in our parameter study can explain naturally a range of core masses 3-30 M⊙ and specific angular momenta 1019-1021 cm2 s-1.

KW - Diffusion

KW - ISM: clouds

KW - ISM: magnetic fields

KW - MHD

KW - Stars: formation

KW - Stars: pre-main-sequence

KW - Stars: rotation

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U2 - 10.1086/176387

DO - 10.1086/176387

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VL - 453

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JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

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