most stars are single ! c. j. lada apj, 640, l63 (2006) 1.from observations: a low binary fraction...
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Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006)
1. From observations: a low binary fraction for late-type stars2. 2/3 of all disk MS stellar systems are composed of single star3. Some implications for star & planet formation
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What were the observations and assumptions
Systematic observations • Mid-late 20th century: for MS F,G stars very high BSF (~70% - 80%)• 1991 : for G stars 2/3 are multiple
But is the BSF for G stars representative of all stars ?
SSF- Single Star FractionBSF- Binary Star Fraction
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• BSF to be a function of Sp only ~30% for M stars• IMF (field & embedded clusters) peak broadly between 0.1 - 0.5Msun most disk stars are M-type
2 recent developmets:
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SSF vs. spectral type-- compiled from literatureConclusion:
• SSF is a function of Sp, 43% for G (Duquennoy1991) to ~74% for M (Delfosse2004)
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Field IMF: broad peak between 0.1~0.5 Msun M type stars
-Muench et al 2002
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Fraction of all stars above H-burning limit that are M stars: 73% for Muench’s IMF78% for Miller-Scalo IMF;84% for PDMF
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The Total Single Star Fraction
• SSF<M =43% (characterized for G stars)• SSFM=74%• MTF=73% or 78%
SSF<M – SSF for earlier than M typeSSFM – SSFfor M type stars
MTF – fraction of all stars that are M-type starsETF=1-MTF – early type fraction
SST(total) = SSF<M×ETF + SSFM×MTF = 66% or 67%
2/3 of all MS primary stars currently residing in the Galactic disk are single stars
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Some discussions
From observations one-to-one mapping of molecular cloud core mass to stellar mass, modified by a SFE of 30%-50%, is possible !
• BSF as function of stellar mass clues to physical process of star formation“if protostellar cores further fragment and produce small-N clusters, the dynamicaldecay of these clusters into binary and single stars can in certain circumstances produce a BSF that declines with decreasing primary mass, similar to what is observed” -Durisen et al. 2001
• Most stars could harbor planetary systems unperturbed by binary companions !?
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BSF