The Theory Of Evolution For Brown Dwarfs

Brown dwarfs have been one of the hottest fields in astronomy for the past 20years.Brown dwarfs are objects which have insufficient mass to sustain stable hydrogen nuclear burning in their cores.Brown dwarfs play an important role in correcting the mass function of galactic objects,promoting the development of astronomical observational technology and studying the low-temperature atmosphere.They are too faint and cold to be directly detected until the year 1995.Researchers use theories of stellar physics and stellar evolution to study brown dwarfs.With the development of observational technology in recent years,several benchmark brown dwarfs have been discovered.These benchmark brown dwarfs are a good test for theoretical model.We use MESA one-dimensional stellar evolution code to study brown dwarfs.We adopt some of the modules applicable to brown dwarfs in MESA,such as SCVH EOS for equation of state and COND atmosphere model.We compared our model with observations of three benchmark brown dwarfs:HD4747B,HD 19467B and Gl 758B.The observations were found to be well agreed with our theoretical model.We use the brown dwarf evolutionary model to simulate the upper and lower mass limits of brown dwarfs.The upper mass limit is the hydrogen burning mass limit.The lower mass limit is the deuterium burning mass limit.We found that although the upper and lower mass limits of brown dwarfs are generally considered to be 0.08M_?and 13M_J,different parameters including helium abundance,metallicity,initial deuterium abundance and rotation can fluctuate these values up and down.We found that higher helium abundance,higher metallicity and slower rotation speed bring down the mass limits of the brown dwarfs.Our results of upper and lower mass limits are consistent with previous work from literature.Our result on upper mass limit is about 0.075M_??0.085M_?.Our results on lower mass limit is about 11.8M_J?15.4M_J.In previous studies from literature,no one has given numerical simulation results for the effect of rotation on the deuterium burning mass limit.We conclude that the mass limit of the brown dwarf differs by about 0.6M_Jat 0.2 times the initial critical rotation speed and without considering rotation.