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| Paper: |
Binary star fraction in star clusters |
| Volume: |
13, The Formation and Evolution of Star Clusters |
| Page: |
443 |
| Authors: |
Romani, Roger W.; Weinberg, Martin D. |
| Abstract: |
An unresolved binary system will be systematically brighter and redder than the primary component alone. These systems may measurably widen the main sequence in the color-magnitude diagram. We show analytically that a 'second sequence' is indeed expected for observed IMFs and standard color-magnitude relations. The relative intensity of the second sequence depends on the steepness of the mass function. For NGC 6341 (M92) and NGC 7099 (M30), we construct a model single-star + binary color-magnitude diagram based on the best fitting isochrones and power-law IMFs. The binary fraction is estimated by maximum likelihood. We find that the highest quality M92 field observed by Stetson and Harris (1988) contains less than about 8 percent binaries. Two fields observed in M30 (Bolte 1987) have a significantly lower fraction of binary candidates, less than about 3 percent. |
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