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Register a new userA New Approach to Determine the Initial Mass Function in the Solar Neighborhood
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Authors
Takuji Tsujimoto
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Oxygen to iron abundance ratios of metal-poor stars provide information on nucleosynthesis yields from massive stars which end in Type II supernova explosions. Using a standard model of chemical evolution of the Galaxy we have reproduced the solar neighborhood abundance data and estimated the oxygen and iron yields of genuine SN II origin. The estimated yields are compared with the theoretical yields to derive the relation between the lower and upper mass limits in each generation of stars and the IMF slope. Independently of this relation, we furthermore derive the relation between the lower mass limit and the IMF slope from the stellar mass to light ratio in the solar neighborhood. These independent relations unambiguously determine the upper mass limit of $m_u=50 pm 10 M_sun$ and the IMF slope index of 1.3 - 1.6 above 1 M_sun. This upper mass limit corresponds to the mass beyond which stars end as black holes without ejecting processed matter into the interstellar medium. We also find that the IMF slope index below 0.5 M_sun cannot be much shallower than 0.8.
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The origin of brown dwarfs (BDs) is still an unsolved mystery. While the standard model describes the formation of BDs and stars in a similar way recent data on the multiplicity properties of stars and BDs show them to have different binary distribution functions. Here we show that proper treatment of these uncovers a discontinuity of the multiplicity-corrected mass distribution in the very-low-mass star (VLMS) and BD mass regime. A continuous IMF can be discarded with extremely high confidence. This suggests that VLMSs and BDs on the one hand, and stars on the other, are two correlated but disjoint populations with different dynamical histories. The analysis presented here suggests that about one BD forms per five stars and that the BD-star binary fraction is about 2%-3% among stellar systems.
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