Fragmentation Of Molecular Clouds Research Articles

Effects of magnetic fields and rotation on the fragmentation of filamentary molecular clouds - Comparison of the theory with the Orion A cloud

view Abstract Citations (54) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of Magnetic Fields and Rotation on the Fragmentation of Filamentary Molecular Clouds: Comparison of the Theory with the Orion A Cloud Hanawa, Tomoyuki ; Nakamura, Fumitaka ; Matsumoto, Tomoaki ; Nakano, Takenori ; Tatematsu, Ken'ichi ; Umemoto, Tomofumi ; Kameya, Osamu ; Hirano, Naomi ; Hasegawa, Tetsuo ; Kaifu, Norio ; Yamamoto, Satoshi Abstract We discuss the fragmentation of a filamentary molecular cloud on the basis of a magnetohydrodynamical stability analysis and the observations of the Orion A cloud with the Nobeyama 45 m telescope. Our model cloud has axial and helical magnetic fields and rotates around the axis. The dispersion relation for this cloud shows that the presence of a magnetic field and/or rotation shortens the wavelength of the most unstable mode, i.e., the mean distance between the adjacent fragments, measured in units of the filament diameter. We compare the theoretical results with the observed clumpy structure of the filamentary Orion A cloud and find that the sum of magnetic and centrifugal forces in the parent cloud was comparable with the pressure force (thermal and turbulent) and has had significant effects on the fragmentation. The rotation velocity of the filament measured in the (C-13)O emission line is consistent with this result. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/186749 Bibcode: 1993ApJ...404L..83H Keywords: Fragmentation; H Ii Regions; Interstellar Magnetic Fields; Magnetohydrodynamic Stability; Molecular Clouds; Rotation; Carbon Monoxide; Emission Spectra; Line Spectra; Astrophysics; HYDROMAGNETICS; INSTABILITIES; ISM: INDIVIDUAL NAME: ORION NEBULA; ISM: MAGNETIC FIELDS full text sources ADS | data products SIMBAD (2) Related Materials (1) Erratum: 1993ApJ...412L..75H

A study of the fragmentation of molecular clouds and the form of initial mass-function for low-mass protostellar fragments

Opacity limited fragmentation is considered for a spherically-collapsing isothermal molecular cloud in a low temperature range where molecular hydrogen and grains are the only cooling and opacity sources. The minimum Jeans mass of a fragment is calculated for different values of the parameters. The form of the initial mass function (IMF) is derived for low-mass protostellar fragments for different values of the parameters. They are discussed and compared with observations. A rough estimate of the cloud mass contained in the brown-dwarf regime is given.

Ambipolar diffusion and star formation: Formation and contraction of axisymmetric cloud cores. I - Formulation of the problem and method of solution

The problem of the formation and contraction of axially symmetric, isothermal, self-gravitating, molecular cloud fragments (or cores) due to ambipolar diffusion in magnetically supported parent clouds is formulated. The numerical method of solution involves a new, very general, fully adaptive, filtered mesh to accurately follow the quasi-static and dynamical phases of evolution. In a test run on a 30 x 30 grid with flux-freezing in the neutrals, the evolution of a supercritical fragment to a central density enhancement of 100,000 was traced. The height and width of the innermost zone decreased by factors of 180 and 45, respectively, and the mass in the central flux tube changed by less than 0.2 percent, which is a negligible amount compared to the change expected when ambipolar diffusion is included.

Gravitational fragmentation - A comparison with W49A

The process of gravitational fragmentation of molecular clouds is investigated through a comparison of numerical and observational results. The expected millimeter wave molecular line emission from a model fragmenting cloud generated by a numerical hydrodynamic simulation is calculated and compared with observations of HCO(+) from the star-forming region W49A. This investigation suggests that the rotating ring of H II regions, the necklace in W49A, may have formed in the gravitational fragmentation of a flattened rotating molecular cloud.

A simulation of the collapse and fragmentation of cooling molecular clouds

The application of the Smoothed Particle Hydrodynamics method to the fragmentation of rotating cloud and disk systems is described, allowing for molecular cooling due to H2 and CO. A novel approach to solving Poisson's equation for disklike structures which exploits the multigrid algorithm is also described. Numerical studies are presented which investigate the evolution of both rotating clouds and Maclaurin disks, in each case with both an isothermal equation of state and with molecular cooling. The results establish the influence of molecular cooling on the fragmentation of molecular clouds. The isothermal sequences, if they fragment at all, do so into far fewer lumps than the cooling sequences. This is not due to a cooling instability as such, but rather to the reduced thermal support. One of the sequences shows a remarkable similarity to the W49A star-forming region.

MHD instabilities and fragmentation of molecular clouds

The properties of the interstellar magnetic clouds, their hierarchy, turbulence and their origin in a processes of the rising of MHD-instabilities are discussed.

MHD instabilities and fragmentation of molecular clouds

The properties of the interstellar magnetic clouds, their hierarchy, turbulence and their origin in a processes of the rising of MHD-instabilities are discussed.

Symposium Summary: Fragmentation and Star Formation in Molecular Clouds

This Symposium on fragmentation and star formation has dealt with the heart of the study of molecular clouds, which is how they form stars. This problem is one of the most profound and challenging problems in all of astrophysics. The complexity of the interstellar medium adds to its difficulty and we cannot expect a quick and easy solution. Nonetheless, the reports presented at this Symposium indicate that substantial progress is being made in this field.

Symposium Summary: Fragmentation and Star Formation in Molecular Clouds

This Symposium on fragmentation and star formation has dealt with the heart of the study of molecular clouds, which is how they form stars. This problem is one of the most profound and challenging problems in all of astrophysics. The complexity of the interstellar medium adds to its difficulty and we cannot expect a quick and easy solution. Nonetheless, the reports presented at this Symposium indicate that substantial progress is being made in this field.

Nature and History of the Organic Compounds in Comets: an Astrophysical View

AbstractThe chemical similarities between comets, carbonaceous chondrites, and interstellar molecules and grains are reviewed first. The evolution of frosty interstellar grains is then followed during the collapse of a molecular cloud fragment and the subsequent formation of the Solar System. The paradigm clarifies the probable origin of the two populations of comets of different symmetry (the Oort Cloud and the Kuiper Belt) and implies an exogenous origin for all carbon and water on Earth. This origin is explained by the orbital diffusion of planetesimals that is required by the growth of protoplanets.

The dust and gas surrounding LkH-alpha 101

The linear polarization of the reflection nebula NGC 1579 and the CO (1 to 0) emission from the associated molecular gas have been mapped for several minutes of arc around the exciting star LkH-alpha 101. These maps show conclusively that LkH-alpha 101 is the sole significant source of illumination in the region. The dust in the reflection nebula appears to be uniform over the illuminated region and is uniformly illuminated by LkH-alpha 101. Despite the patchy obscuration, the dark cloud which obscures LkH-alpha 101 does not surround the star. LkH-alpha 101 may have formed out of a placental cloud whose remnants now include four molecular cloud fragments, two in front of and two behind the reflection nebula, as well as an H I cloud previously detected in the region.

High-resolution infrared observations in IC 5146

view Abstract Citations (10) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution infrared observations in IC 5146. Wilking, B. A. ; Harvey, P. M. ; Joy, M. Abstract High-resolution near-infrared and far-infrared observations are presented of the southeastern molecular cloud fragment in the IC 5146 dark cloud. These observations rule out earlier suggestions for the formation of massive stars in this fragment. Publication: The Astronomical Journal Pub Date: April 1984 DOI: 10.1086/113540 Bibcode: 1984AJ.....89..496W Keywords: Astronomical Spectroscopy; High Resolution; Infrared Astronomy; Molecular Clouds; Emission Spectra; Far Infrared Radiation; Spectral Resolution; Stellar Evolution; Astronomy full text sources ADS | data products SIMBAD (3)

General physical characteristics of the interstellar molecular gas

The interstellar medium may be characterized by several physically rather distinct regimes: coronal gas, intercloud gas, diffuse clouds, isolated dark clouds and globules (of small to modest mass), more massive molecular clouds containing OB (and later) stars, and giant molecular clouds. Molecules first appear in the denser diffuse clouds, and occur everywhere that AV ≳ 1m. Values of temperature, density, ionization fraction, mass, size, and velocity field are discussed for each regime. Heating and cooling mechanisms are reviewed. Nearly all molecular clouds exceed the Jeans criteria for gravitational instability, yet detailed models reveal no cases where observations can be interpreted unambiguously in terms of rapid collapse. The possibility that clouds are supported by turbulence, rotation, or magnetic fields is discussed, and it is concluded that none of these agencies suffice. Comments are made about fragmentation and star formation in molecular clouds, with possible explanations for why only low mass stars form in low mass clouds, why early-type stars form only in clouds with masses ≳ 103 M⊙, and why O-stars seem to form near edges of clouds. Finally, large-scale interactions between molecular clouds and the galactic disk stellar population are discussed.

The locations of newly formed stars in molecular clouds

Observations of very massive stars (M≥10M⊙) are suggestive of a star formation process which requires an external trigger. However, observations pertaining to the formation of stars of lower mass (M≤9M⊙) require no such triggering mechanism and are consistent with the idea that such stars form as a natural consequence of the evolution, gravitational collapse and fragmentation of a proto-stellar molecular cloud.

CO and H2O observations of the H II region NGC 281

view Abstract Citations (56) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CO and H2O observations of the H II region NGC 281. Elmegreen, B. G. ; Lada, C. J. Abstract Two molecular cloud fragments that appear to be separated by a channel of ionized gas at the southern edge of the H II region were detected by CO observations of the region around NGC 281. Near an H2O maser discovered at the northern edge of one cloud, near the interface between the cloud and the H II region, 12-CO temperatures and line widths reach a maximum value. Since a ridge of enhanced continuum emission from the H II region is also found to be coincident with the maser position, it is thought that the maser source is adjacent to an ionization front which is progressing into the back side of the molecular cloud. The dynamical history of the region is considered, and it is suggested that the proximity of the maser to the edge of the molecular cloud could indicate that gravitational instabilities detected there may already have resulted in star formation. Publication: The Astrophysical Journal Pub Date: January 1978 DOI: 10.1086/155801 Bibcode: 1978ApJ...219..467E Keywords: Carbon Monoxide; H Ii Regions; Interstellar Masers; Water Masers; Astronomical Maps; Gravitational Collapse; Hydrogen Ions; Interstellar Chemistry; Nebulae; Stellar Evolution; Astrophysics; Dynamics:H II Regions; Masers:Molecular Clouds full text sources ADS | data products SIMBAD (2)