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ItemFinding the Elusive Substellar Members of Young Moving Groups([Honolulu] : [University of Hawaii at Manoa], [December 2016], 2016-12)Young moving groups (YMGs) consist of coeval, comoving stars, with ages between 10–100 Myrs, that have migrated from their origins after formation. They provide a valuable link between ongoing star formation in molecular clouds (~ 1 Myr) and old field stars (� 1 Gyr). However, previous searches based on optical surveys such as Hipparcos and the Palomar Sky Survey were insensitive to these very faint cool dwarfs. More recent surveys with GALEX have begun to reveal the nearby (< 25 pc) low-mass members (� 0.1 M8) but the cool, substellar members have remained elusive. We have increased the search volume by a factor of ~ 10 using a novel combination of photometry and proper motions from Pan-STARRS, WISE, and 2MASS in order to uncover the missing substellar members down to ~ 0.01 M8 (at 10 Myr). We have obtained NIR low-resolution spectroscopy and confirmed the youth of 65 new ultracool dwarf YMG candidates. We also obtained high-resolution NIR spectroscopy to determine radial velocities for our young brown dwarfs. With our RVs and PS1 parallaxes, we have nearly doubled the number of confirmed bona fide substellar YMG members, which are also brown dwarf age benchmarks. Our new young brown dwarfs empirically define the substellar spectral evolution with age and provide us with a snapshot of brown dwarf evolution. Finally, our resulting young brown dwarfs will be valuable targets for future surveys of brown dwarf binarity and young exoplanet characterization.
ItemThe Initial Mass Function of Westerlund 1 Based on High Spatial Resolution HST Data([Honolulu] : [University of Hawaii at Manoa], [December 2013], 2013-12)Westerlund 1 is one of the most massive young star clusters in the Milky Way. We use precise photometry and astrometry from the Hubble Space Telescope to derive the fundamental properties of the cluster, including the initial mass function. Cluster membership probabilities are estimated using proper motions and photometry and 615 stars have membership probabilities above 90%. By comparing the cluster members with synthetic cluster models and Bayesian inference, we obtain the distance to the cluster 3:8 ± 0:2kpc, the age 14.7Myrs, and the average extinction Aks to the cluster 0:75 ± 0:01amg with an extinction variation 0:12 ± 0:02mag. The initial mass function is fit by a single power-law down to 1M☉ with an index of-1:58 ± 0:16, inconsistent with the "universal value" found in other low mass clusters (e.g. Orion), but consistent with the other starburst cluster (eg: Arches). We also find that the stellar evolution and atmosphere models do not match with our data in the pre-main sequence region. More improvement in the models are required in the future.