Prolate Clouds Research Articles

Spheroidal models of magnetic clouds and their comparison with spacecraft measurements

We present here magnetic force‐free solutions for spherical, oblate, and prolate clouds and show their magnetic field configurations. It is shown that spheroidal models can fit observed clouds as well as the cylindrical model. The spherical model is free of the limitation of the cylindrical model that allows only reduced increase of the magnetic field to 2x of the boundary value following from properties of the Bessel functions. For the tested cases, the cloud diameters following from the fit are generally larger for the spherical model than for the cylindrical one. An analysis of 14 cases shows that the fit using the spherical model is of a comparable accuracy in comparison with the cylindrical model. Generally, no exact determination of the cloud boundaries has been given up to now. We try to estimate cloud boundaries from the plasma data as an independent check, and compare them with cloud boundaries following from models of magnetic clouds. The boundaries given by the spheroidal models are near irregular temperature increases, and we suggest taking these increases as a possible indicator of the cloud physical boundaries.

Gas and dust in the pre-main-sequence multiple system GG Tauri

We present 1.4 and 2.7 mm aperture synthesis maps of the gas and dust continuum emission around GG Tauri, a very young component of a premain-sequence multiple star system; both GG Tau and its apparent companion, GG Tau/c, at 1500 AU separation, are themselves binaries. At 1.4 mm, dust continuum emission of about 750 AU in extent is associated with GG Tau, and a secondary peak is near GG Tau/c. Spectral line images reveal gaseous structure around GG Tau, elongated along the GG Tau-GG Tau/c axis. There is some suggestion that the gas associated with GG Tau/c alone is extended in a different direction. Marked changes in the morphology and velocity structure of the molecular emission near GG Tau/c also indicate that this system is differently oriented. Clumps between the two systems may be vestiges of a connecting bar. GG Tau and GG Tau/c appear to have originated in a common cloud; their different systemic orientations suggest that they formed from an initially prolate cloud rather than from an extensive and highly flattened disk.

Interstellar cloud shapes - A minimum-hypothesis account involving a purely gravitational effect

The effect produced by the anisotropic gravitational field on the shape of a nonspherical, self-gravitating interstellar cloud is examined. The projected axial ratios observed for molecular clouds can be accounted for if clouds are not generally in a state of strict dynamical equilibrium. For clouds having spectral line widths dominated by supersonic turbulent motions, this purely gravitational effect predicts a mean true axial ratio q about 0.3 for both oblate and prolate cloud geometries. Clouds having p less than about 0.3 are likely to be prolate and quite elongated. The observational data on molecular cloud cores, which have essentially thermal line widths, can be fitted equally well to either oblate or prolate spheroids having q between 0.1 and 0.4 with q about 0.2 providing the best match: highly elongated cores are again more likely to be prolate. While other processes certainly operate throughout the Galaxy to influence cloud shape, it appears plausible that at least some clouds may be shaped principally by their anisotropic gravitational field.

The distribution of galaxies around NGC 5846

view Abstract Citations (19) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Distribution of Galaxies Around NGC 5846 Haynes, M. P. ; Giovanelli, R. Abstract The three-dimensional distribution of galaxies in a region surrounding the chain of galaxies in the NGC 5846 group has been investigated by both subjective and objective tests for clustering. The compilation of a complete redshift sample over the area of study allows the identification of distinct galaxy aggregates and estimation of group properties. Much of the nearby structure, including the NGC 5846 group, is connected into a single prolate cloud of galaxies that points toward the Virgo cluster. Also evident is a tenuous filament of galaxies at a velocity of ~7000 km s^-1^ that appears to connect at right angles with an elongated cloud that is identified as the Zw 1400+0949 cluster seen in projection. The subconcentration around NGC 5846 is itself a tight, compact configuration, unlike other density enhancements like the Virgo III or Ursa Major Clouds. A comparison of the NGC 5846 group with similar structures in the Local Supercluster confirms the qualitative impression that the highest density environments are dominated by early type systems. Publication: The Astronomical Journal Pub Date: September 1991 DOI: 10.1086/115915 Bibcode: 1991AJ....102..841H Keywords: Galactic Structure; Red Shift; Spatial Distribution; Virgo Galactic Cluster; Spiral Galaxies; Universe; X Ray Sources; Astronomy; GALAXIES: CLUSTERING; GALAXIES: REDSHIFTS full text sources ADS | data products SIMBAD (105) NED (101)

The collapse of cylindrical isothermal and polytropic clouds with rotation

view Abstract Citations (22) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Collapse of Cylindrical Isothermal and Polytropic Clouds with Rotation Bonnell, Ian ; Bastien, Pierre Abstract Two-dimensional numerical hydrodynamic calculations are carried out to study the effect of the geometry on the process of gravitational collapse of a rotating axisymmetric cloud. Both polytropic and isothermal equations of state are used in the analysis. It is shown that the shape of a cloud undergoing collapse is the dominant factor in all cases, except where the polytropic constant is large (greater than 4/3). Without rotation, clouds differing from a uniform geometry collapse more readily, while the rotating oblate clouds require a larger initial Jeans number than either clouds with L/D = 1 or prolate clouds. Publication: The Astrophysical Journal Pub Date: June 1991 DOI: 10.1086/170147 Bibcode: 1991ApJ...374..610B Keywords: Gravitational Collapse; Isothermal Processes; Molecular Clouds; Polytropic Processes; Star Formation; Stellar Rotation; Astronomical Models; Computational Astrophysics; Hydrodynamics; Jeans Theory; Astrophysics; HYDRODYNAMICS; STARS: FORMATION; STARS: ROTATION full text sources ADS |

Effect of the geometric shape of an exploding cloud and the location of initiation of combustion on the parameters of the blast wave

When burning gases accidentally flow out into an unbounded space, a dangerously explosive cloud, whose shape depends on the conditions of outflow, the meteorological conditions, and the properties of the gas, forms [i]. Gases such as propane, propylene, butadiene, and others whose density i~ greater than that of air form an oblate cloud, whose height is less than its transverse dimensions. If the source of burning gas operates continuously and a wind is blowing, then a prolate cloud, characterized by the fact that one dimension (length) is much greater than the other dimensions, can form. Other forms of dangerously explosive clouds can also form: Thus, in the case when gas flows out of a pipeline or a reservoir a jet forms with an internal distribution of the concentration of hot gas such that a dangerously explosive cloud whose shape is close to that of an ellipsoid of revolution with the ratio between the axes depending on the velocity of outflow and the size of the source forms.

The thermal effects of H2 molecules in rotating and collapsing spheroidal gas clouds

view Abstract Citations (127) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The thermal effects of H2 molecules in rotating and collapsing spheroidal gas clouds. Hutchins, J. B. Abstract The thermal evolution of a protogalactic density perturbation within the expanding background of various Friedmann universes is studied for the case of a uniform pressure-free spheroid which reaches its maximum extension at some time, undergoes homologous collapse, and rotates as a solid body for times later than the time of maximum extension. Cooling of the cloud by radiation in the rotational lines of H2 molecules formed through various reactions is investigated in order to determine the Jeans mass. Dynamic processes during the precollapse epoch are analyzed, and a theory of heat exchange with the radiation field through rotational transitions of H2 molecules in their electronic and vibrational ground states is developed. Conditions on the matter temperature and electron concentration at the time of maximum extension are presented as explicit functions of the background model parameter and the time of maximum extension. The chemical reaction equations and rates of importance during collapse are discussed, and the collapse dynamics is considered. The thermal effects of H2 molecules are examined as functions of the background model, the time of maximum extension, the initial axial ratio, and rotation for initially spherical, oblate, and prolate clouds. Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154254 Bibcode: 1976ApJ...205..103H Keywords: Hydrogen Clouds; Molecular Gases; Rotating Matter; Stellar Evolution; Temperature Effects; Astronomical Models; Gravitational Collapse; Heat Transfer; Oblate Spheroids; Perturbation Theory; Prolate Spheroids; Stellar Mass; Astrophysics full text sources ADS |