scholarly journals Variation of the core lifetime and fragmentation scale in molecular clouds as an indication of ambipolar diffusion

2021 ◽  
Author(s):  
I. Das ◽  
S. Basu ◽  
P. Andre
Keyword(s):  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
The Core

AMBIPOLAR DIFFUSION AND TURBULENT MAGNETIC FIELDS IN MOLECULAR CLOUDS

2011 ◽  
Vol 26 (04) ◽  
pp. 235-249 ◽  
Author(s):  
MARTIN HOUDE ◽  
TALAYEH HEZAREH ◽  
HUA-BAI LI ◽  
THOMAS G. PHILLIPS
Keyword(s):  
Magnetic Fields ◽  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Star Forming ◽  
Star Forming Regions ◽  
Spin Interactions ◽  
Line Narrowing ◽  
Weakly Ionized ◽  
Novel Method

We review the introduction and development of a novel method for the characterization of magnetic fields in star-forming regions. The technique is based on the comparison of spectral line profiles from coexistent neutral and ion molecular species commonly detected in molecular clouds, sites of star formation. Unlike other methods used to study magnetic fields in the cold interstellar medium, this ion/neutral technique is not based on spin interactions with the field. Instead, it relies on and takes advantage of the strong cyclotron coupling between the ions and magnetic fields, thus exposing what is probably the clearest observational manifestation of magnetic fields in the cold, weakly ionized gas that characterizes the interior of molecular clouds. We will show how recent development and modeling of the ensuing ion line narrowing effect leads to a determination of the ambipolar diffusion scale involving the turbulent component of magnetic fields in star-forming regions, as well as the strength of the ordered component of the magnetic field.

scholarly journals Filament Formation in Molecular Clouds as a Scale-Free Process

2015 ◽  
Vol 11 (A29B) ◽  
pp. 709-710
Author(s):  
Enrique Vázquez-Semadeni ◽  
Gilberto Gómez
Keyword(s):  
Hierarchical Structure ◽  
Molecular Clouds ◽  
Large Scale ◽  
Filament Formation ◽  
Molecular Line ◽  
Scale Free ◽  
The Core ◽  
Free Process ◽  
Self Gravity

AbstractWe discuss the formation of filaments in molecular clouds (MCs) as the result of large-scale collapse in the clouds. We first give arguments suggesting that self-gravity dominates the nonthermal motions, and then briefly describe the resulting structure, similar to that found in molecular-line and dust observations of the filaments in the clouds. The filaments exhibit a hierarchical structure in both density and velocity, suggesting a scale-free nature, similar to that of the cosmic web, resulting from the domination of self-gravity from the MC down to the core scale.

A physically motivated core definition applied to dust emission observations of the Pipe nebula

2018 ◽  
Vol 14 (S345) ◽  
pp. 259-260
Author(s):  
Birgit Hasenberger ◽  
João Alves
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Molecular Clouds ◽  
Dust Emission ◽  
Core Sample ◽  
Critical Stage ◽  
The Core ◽  
Dense Cores ◽  
A New Technique ◽  
Cloud Medium

AbstractDense cores represent a critical stage in the star-formation process, but are not physically well-defined entities. We present a new technique to define core boundaries in observations of molecular clouds based on the physical properties of the cloud medium. Applying this technique to regions in the Pipe nebula, we find that our core boundaries differ from previous analyses, with potentially crucial implications for the statistical properties of the core sample.

H 2 , H 3 + and the age of molecular clouds and prestellar cores

2012 ◽  
Vol 370 (1978) ◽  
pp. 5200-5212 ◽  
Author(s):  
L. Pagani ◽  
P. Lesaffre ◽  
E. Roueff ◽  
M. Jorfi ◽  
P. Honvault ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Initial Conditions ◽  
Molecular Gas ◽  
New Approach ◽  
The Core ◽  
Dense Cores ◽  
Prestellar Cores ◽  
Deuterium Enrichment ◽  
Abundance And Distribution ◽  
Static Core

Measuring the age of molecular clouds and prestellar cores is a difficult task that has not yet been successfully accomplished although the information is of paramount importance to help in understanding and discriminating between different formation scenarios. Most chemical clocks suffer from unknown initial conditions and are therefore difficult to use. We propose a new approach based on a subset of deuterium chemistry that takes place in the gas phase and for which initial conditions are relatively well known. It relies primarily on the conversion of H 3 + into H 2 D + to initiate deuterium enrichment of the molecular gas. This conversion is controlled by the ortho/para ratio of H 2 that is thought to be produced with the statistical ratio of 3 and subsequently slowly decays to an almost pure para-H 2 phase. This slow decay takes approximately 1 Myr and allows us to set an upper limit on the age of molecular clouds. The deuterium enrichment of the core takes longer to reach equilibrium and allows us to estimate the time necessary to form a dense prestellar core, i.e. the last step before the collapse of the core into a protostar. We find that the observed abundance and distribution of DCO + and N 2 D + argue against quasi-static core formation and favour dynamical formation on time scales of less than 1 Myr. Another consequence is that ortho-H 2 remains comparable to para-H 2 in abundance outside the dense cores.

scholarly journals Probing the turbulent ambipolar diffusion scale in molecular clouds with spectroscopy

2013 ◽  
Vol 438 (1) ◽  
pp. 663-671 ◽  
Author(s):  
T. Hezareh ◽  
T. Csengeri ◽  
M. Houde ◽  
F. Herpin ◽  
S. Bontemps
Keyword(s):  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Diffusion Scale
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