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  • 1
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    Experimental constraints on the origin of chondrules (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Chrondule formation was an important (perhaps ubiguitous) process in the early solar system, yet their origins remain elusive. Some points, however, are clear. The precursor material of chondules (dust) was rapidly heated at rates of perhaps thousands of degrees per second and was cooled more slowly. It was proposed to investigate chondrule formation in the Space Station environment via a dust-box (a chamber in which dust can be suspended, heated, and cooled. A microgravity environment is conducive to this kind of experiment because of the significant retardation of settling rates compared with a terrestrial laboratory environment. These long-duration experiments might require the development of technologies to counteract even the small, but finite and permanent gravitation field of the Space Station. Simple, but interesting experiments on dust suspensions immediately present themselves.
    Keywords: ASTROPHYSICS
    Type: NASA, Lyndon B. Johnson Space Center, Experiments in Planetary and Related Sciences and the Space Station; 2 p
    Format: application/pdf
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  • 2
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    Submillimeter observations of evolved stars (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Broadband submillimeter observations of thermal emission from several evolved stars have been obtained using the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. The observations were carried out at an effective wavelength of 400 microns in order to estimate the mass loss rates in dust from the stars. Direct estimates of mass loss rates are in the range 10 to the -9th to 10 to the -6th solar mass/yr. Analysis of the spectrum of IRC + 10216 confirmed previous estimates of dust grain emissivity in the range 10-1000 microns. The infrared properties of IRC + 10216 are found to be similar to the carbon rich object CRL 3068. No systematic difference was found between the dust masses of carbon rich and oxygen rich envelopes. The largest mass loss rates in dust were obtained for the bipolar objects OH 231.8 + 4.2 CRL 2688, CRL 618, and NGC 7027. It is suggested that the ratios of gas to dust, and the slopes of the far infrared to submillimeter wavelength continua of these stars objects are probably representative of amorphous rather than crystalline grains.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 294; 242-255
    Format: text
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  • 3
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    Magnetic fields and stardust (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The purpose of this paper is to outline the principles governing the use of far-infrared and submillimeter polarimetry to investigate magnetic fields and dust in interstellar clouds. Particular topics of discussion are the alignment of dust grains in dense clouds, the dependence on wavelength of polarization due to emission or to partial absorption by aligned grains, the nature of that dependence for mixtures of grains with different properties, and the problem of distinguishing between (1) the effects of the shapes and dielectric functions of the grains and (2) the degree and direction of their alignment.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Quarterly Journal (ISSN 0035-8738); 29; 327-351
    Format: text
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  • 4
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    Polarization of far-infrared radiation from molecular clouds (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The paper reports measurements of the polarization of far-infrared emission from dust in nine molecular clouds. Detections were obtained in Mon R2, in the Kleinmann-Low (KL) nebula in Orion, and in Sgr A. Upper limits were set for six other clouds. A comparison of the 100 micron polarization of KL with that previously measured at 270 microns provides new evidence that the polarization is due to emission from magnetically aligned dust grains. Comparing the results for Orion with measurements at optical wavelengths, it is inferred that the magnetic field direction in the outer parts of the Orion cloud is the same as that in the dense core. This direction is nearly perpendicular to the ridge of molecular emission and is parallel to both the molecular outflow in KL and the axis of rotation of the cloud core. In Mon R2, the field direction which the measurements imply does not agree withthat derived from 0.9-2.2 micron polarimetry. The discrepancy is attributed to scattering in the near-infrared. In Orion and Sgr A, where comparisons are possible, the measurements are in good agreement with 10 micron polarization measurements.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 345; 802-810
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  • 5
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    Magnetic alignment of grains (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper reviews mechanisms that have been proposed to account for alignment of dust grains in diffuse clouds and in dense clouds. The mechanisms that have proved inadequate are considered, including alignment by nonmagnetic and magnetic processes. The results thus far favor the Davis-Greenstein mechanism, in which paramagnetic relaxation of spinning grains removes components of rotation perpendicular to the magnetic field. Polarization measurements showing the alignment of grains in cool dense clouds are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters and Communications (ISSN 0888-6512); 26; 3-5
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  • 6
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    Experimental constraints on heating and cooling rates of refractory inclusions in the early solar system (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The refractory inclusions in carbonaceous chondrites were the subject of considerable interest since their discovery. These inclusions contain minerals that are predicted to be some of the earliest condensates from the solar nebula, and contain a plethora of isotopic anomalies of unknown origin. Of particular interest are those coarse-grained inclusions that contain refractory metal particles (Fe, Ni, Pt, Ru, Os Ir). Experimental studies of these inclusions in terrestrial laboratories are, however, complicated because the dense particles tend to settle out of a molten or partially molten silicate material. Heating experiments in the Space Station technology and microgravity in order to observe the effects of metal nuggets (which may act as heterogeneous nucleation sites) on nucleation rates in silicate systems and to measure simultaneously the relative volatilization rate of siderophile and lithophile species. Neither experiment is possible in the terrestrial environment.
    Keywords: ASTROPHYSICS
    Type: NASA, Lyndon B. Johnson Space Center, Experiments in Planetary and Related Sciences and the Space Station; 1 p
    Format: text
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