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1.6 Stellar IMF- Variations in high stellar density
Variation in IMF is observed from region to region. Salpeter’s function gives a steep fall in the case of massive stars, i.e stars with masses greater than 5M?. Many authors have explored the IF in many situations – in the field versus in clusters, in galaxies with different morphologies etc. In 1979 Miller and Scalo derive a mass function of stars in the solar neighbourhood. They fitted it with a lognormal function and obtained a slope steeper than the Salpeter slope in the high mass region19.They made studies in the low mass region and came to the conclusion that the number of stars in the solar and sub-solar region in the solar neighbourhood is less than the extrapolated Salpeter mass function. In 1987 Rana proposed a mass function for the solar neighbourhood within a range of 0.08 to 100M?. As said earlier mass of a star is calculated from its luminosity, there should be a lower limit for the mass of a star to be detected. 0.1 M? is usually used as the lower mass limit of a star 20.
Results of previous works on the IMF are the following. In 1955 Salpeter found a power law function with slope ? ~ -1.35. He introduced the function based on the population of stars that could be observed in those days. At present the stellar population that is accessible to observations is somewhat different. Investigations of Scalo resulted in a function with slope ? ~ -1.7, for intermediate to high mass stars. Rana obtained a slope ? ~ -1.8 for M ; 1.6M?. Further studies leads to the conclusion, which says that slope of low density regions are steep and slope of high density regions, are shallow 21.

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