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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 stars 2.2/3 of all disk MS stellar systems.

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Presentation on theme: "Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006) 1.From observations: a low binary fraction for late-type stars 2.2/3 of all disk MS stellar systems."— Presentation transcript:

1 Most Stars Are Single ! C. J. Lada ApJ, 640, L63 (2006) 1.From observations: a low binary fraction for late-type stars 2.2/3 of all disk MS stellar systems are composed of single star 3.Some implications for star & planet formation

2 What were the observations and assumptions Systematic observations  Mid-late 20th century: for MS F,G stars  very high BSF (~70% - 80%)BSF 1991 : for G stars  2/3 are multiple But is the BSF for G stars representative of all stars ? SSF- Single Star Fraction BSF- Binary Star Fraction

3 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:

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 { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/13/4046519/slides/slide_7.jpg", "name": "The Total Single Star Fraction SSF

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 !?

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