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Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006)

Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006). From observations : a low binary fraction for late-type stars 2/3 of all disk MS stellar systems are composed of single star Some implications for star & planet formation. What were the observations and assumptions.

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Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006)

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  1. Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006) • From observations: a low binary fraction for late-type stars • 2/3 of all disk MS stellar systems are composed of single star • Some implications for star & planet formation

  2. What were the observations and assumptions SSF- Single Star Fraction BSF- Binary Star Fraction • 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 ?

  3. 2 recent developmets: • 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

  4. SSF vs. spectral type -- compiled from literature • Conclusion: • SSF is a function of Sp, • 43% for G (Duquennoy1991) • to ~74% for M (Delfosse2004)

  5. Field IMF: broad peak between 0.1~0.5 Msun  M type stars -Muench et al 2002

  6. Fraction of all stars above H-burning limit that are M stars: 73% for Muench’s IMF 78% for Miller-Scalo IMF; 84% for PDMF

  7. The Total Single Star Fraction SSF<M – SSF for earlier than M type SSFM – SSFfor M type stars MTF – fraction of all stars that are M-type stars ETF=1-MTF – early type fraction • SSF<M =43% (characterized for G stars) • SSFM=74% • MTF=73% or 78% 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

  8. 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 dynamical • decay 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 !?

  9. BSF

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