The Initial Mass Function of Very Low Mass Stars and the Significance of Brown Dwarfs
In recent years we have learned how tricky is the determination of the IMF at the low luminosity end of the main sequence. I recall here the main reasons why the stellar structure computations produce a functional form of the mass-luminosity relation for M ≤ 0.5M ⊙ which, coupled with the observationally determined luminosity function in the visual band, produces a smoothly increasing IMF down to M=0.1M ⊙.
I discuss then the updates of the theory and the large errors which still weigh on the derivation of luminosity and effective temperature from the observational data.
I further consider whether the recent detection of several infrared (substellar?) companions to intrinsically faint stars may give us further hints on the mass-luminosity relation close to the end of the main sequence, and, second, to the number density expected for single brown dwarfs in the galactic disk.
I finally review the problems emerging from the consideration of the luminosity function based on stellar counts in the infrared bands.
KeywordsGlobular Cluster Main Sequence Luminosity Function Galactic Disk Main Sequence Star
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