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1-10 Myr-old low mass stars and brown dwarfs in nearby star forming regions

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Abstract

My thesis research has focused primarily on identifying and characterizing pre-main sequence stars in nearby star-forming regions. To this end, I carried out wide-field (~150-250 deg(2)) optical photometric and spectroscopic surveys in and near the star forming regions of Taurus and Upper Scorpius. In Taurus, the aim of my optical photometric/spectroscopic survey was specifically to probe for a population of intermediate-age pre-main sequence stars outside of the young subclusters that are known to contain most of the young Taurus population. From this work I found tens of young (~1-3 Myr) and intermediate-age (~5-10 Myr) stars both near the known Taurus population and to the east, but relatively few pre-main sequence stars of any age to the west. I argued that the new pre-main sequence stars identified far from Taurus can not have originated from the vicinity of the 1-2 Myr-old subclusters and I proposed instead that they comprise a new, previously undiscovered region of recent star formation. In USco, the aim of my optical photometric/spectroscopic survey was to probe beyond previously explored regions to identify large numbers of 5 Myr-old low mass stars. From the spectroscopic data I have discovered 145 low mass members of USco. Using Monte Carlo simulations I showed that, taking into account known observational errors, the observed age dispersion for the low mass population in USco is consistent with all stars forming in a single burst ~5 Myr ago. I also derived the first spectroscopic mass function for USco that extends into the substellar regime and compared results to similar mass functions derived for stars in four other young clusters and associations.

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