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  • 1
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    Open-system behavior during chondrule formation (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The question of whether chondrules behaved as open systems during formation is crucial to our understanding of both chondrule and chondrite formation. The very large range of chondrule types is best summarized by the compositional classification scheme, wherein the primitive chondrule groups (i.e., those not produced by metamorphic processes) are A1, A2, A5, and B1. In the Semarkona (LL3.0) chondrite, 10.5%, 25.0%, 5.0%, and 56.9% (by number) of the chondrules are groups A1, A2, A5, and B1, respectively. We argue that groups A1 and A2 were produced by reduction and evaporation during chondrule formation of material originally resembling group B1 chondrules.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Papers Presented to the Conference on Chondrules and the Protoplanetary Disk; p 37-38
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Time-series photometric spot modeling. 2: Fifteen years of photometry of the bright RS CVn binary HR 7275 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present a time-dependent spot modeling analysis of 15 consecutive years of V-band photometry of the long-period (P(sub orb) = 28.6 days) RS CVn binary HR 7275. This baseline in time is one of the longest, uninterrupted intervals a spotted star has been observed. The spot modeling analysis yields a total of 20 different spots throughout the time span of our observations. The distribution of the observed spot migration rates is consistent with solar-type differential rotation and suggests a lower limit of the differential-rotation coefficient of 0.022 +/-0.004. The observed, maximum lifetime of a single spot (or spot group) is 4.5 years, the minimum lifetime is approximately one year, but an average spot lives for 2.2 years. If we assume that the mechanical shear by differential rotation sets the upper limit to the spot lifetime, the observed maximum lifetime in turn sets an upper limit to the differential-rotation coefficient, namely 0.04 +/- 0.01. This would be differential rotation just 5 to 8 times less than the solar value and one of the strongest among active binaries. We found no conclusive evidence for the existence of a periodic phenomenon that could be attributed to a stellar magnetic cycle.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 282; 2; p. 535-546
    Format: text
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    NASA TECHNICAL REPORTS
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