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Title: Cool dwarfs and their mass function from infrared surveys
Author: Deacon, N. R.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2002
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Low mass stars and brown dwarfs in the field are usually identified by either infrared surveys or by proper motion surveys. Here these techniques are combined for the first time to produce an infrared proper motion survey. This has produced a sample of over 7000 low mass objects with proper motions greater than 0.1”/yr. It has also found several common proper motion binary systems and SIPS1259-4336, an M8.5 dwarf with a measured parallax of 276 ± 41 millarcseconds. This sample on its own will not yield a constraint on the mass function. In the field the range of ages and the luminosity evolution of objects leads to the mass function being intertwined with the stellar birthrate. Here this problem is dealt with detailed simulations. By drawing ages from a birthrate and masses from a mass function simulated objects can have space positions, velocities and absolute magnitudes assigned using a simple model of the Galaxy, evolutionary models of low mass objects and empirical relations. These can then be converted into observables and passed through a survey selection mechanism. By varying the underlying birthrate and mass function the effect these have on the survey results can be found. These results can then be compared with those of the actual survey to constrain the mass function and birthrate. Here the mass function parameter α is found to be 0.49±0.27 in the range 0.15M m > 0.075Mand the birthrate parameter β is 0.020±0.040. Finally the results of the future infrared surveys by UKIDSS are simulated and the potential constraints that could be set by them outlined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available