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  • 1
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    Initiating solar system formation through stellar shock waves (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Isotopic anomalies in presolar grains and other meteoritical components require nucleosynthesis in stellar interiors, condensation into dust grains in stellar envelopes, transport of the grains through the interstellar medium by stellar outflows, and finally injection of the grains into the presolar nebula. The proximity of the presolar cloud to these energetic stellar events suggests that a shock wave from a stellar outflow might have initiated the collapse of an otherwise stable presolar cloud. We have begun to study the interactions of stellar shock waves with thermally supported, dense molecular cloud cores, using a three spatial dimension (3D) radiative hydrodynamics code. Supernova shock waves have been shown by others to destroy quiescent clouds, so we are trying to determine if the much smaller shock speeds found in, e.g., asymptotic giant branch (AGB) star winds, are strong enough to initiate collapse in an otherwise stable, rotating, solar-mass cloud core, without leading to destruction of the cloud.
    Keywords: SOLAR PHYSICS
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 155-156
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    NASA TECHNICAL REPORTS
  • 2
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    Large-scale processes in the solar nebula (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Theoretical models of the structure of a minimum mass solar nebula should be able to provide the physical context to help evaluate the efficacy of any mechanism proposed for the formation of chondrules or Ca, Al-rich inclusions (CAI's). These models generally attempt to use the equations of radiative hydrodynamics to calculate the large-scale structure of the solar nebula throughout the planet-forming region. In addition, it has been suggested that chondrules and CAI's (=Ch&CAI's) may have been formed as a direct result of large-scale nebula processing such as passage of material through high-temperature regions associated with the global structure of the nebula. In this report we assess the status of global models of solar nebula structure and of various related mechanisms that have been suggested for Ch and CAI formation.
    Keywords: SOLAR PHYSICS
    Type: Lunar and Planetary Inst., Papers Presented to the Conference on Chondrules and the Protoplanetary Disk; p 2-3
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Chondrule formation by clumpy accretion onto the solar nebula (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Chondrule textures and compositions appear to require rapid heating of precursor grain aggregates to temperatures in the range 1500 K to 2100 K, cooling times on the order of hours, and episodic and variable intensity events in order to produce chondrule rims and chemically distinct groups. Nebula shock waves have been proposed by Hood and Horanyi as a physical mechanism that may be capable of meeting the meteoritical constraints. Motivated by astronomical observations of the close environments of young stars, we suggest that the source of the nebula shock waves may be clumpy accretion onto the solar nebula - that is, episodic impacts onto the nebula by discrete cloud clumps with masses of at least 10(exp 22) g. If the cloud clumps are massive enough (10(exp 26) g), the resulting shockwave may be able to propagate to the midplane and process precursor aggregates residing in a dust sub-disk.
    Keywords: SOLAR PHYSICS
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 153-154
    Format: text
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  • 4
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    Midplane temperatures in the solar nebula (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Cosmochemical analyses of meteorites imply that maximum temperatures in the inner solar nebula were on the order of 1300 K, yet standard viscous accretion disk models predict much lower midplane temperatures (approx. 300 K at 2 AU to 3 AU) in a minimum mass nebula. A second-order accurate radiative hydrodynamics code has been used to construct models of the late-phase solar nebula appropriate for low-mass star formation (M is approximately 10(exp -6) to 10(exp -5) solar-M yr(exp -1). For a minimum mass (0.02 solar-M) nebula and a solar-mass protostar, the new models show that compressional heating due to mass accretion onto the nebula and subsequent vertical contraction of the nebula are sufficient to lead to midplane temperatures T(sub m) greater than 1400 K at 1 AU and T(sub m) greater than 1000 K at 2.5 AU.
    Keywords: SOLAR PHYSICS
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 151-152
    Format: text
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