UBC Theses and Dissertations

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UBC Theses and Dissertations

Three dimensional velocity tomography in the core of Messier 71 Samra, Raminder Singh


Using the Gemini North Telescope at Mauna Kea, Hawaii, we have obtained astrometric and spectroscopic data for stars in the core of the galactic globular cluster Messier 71 (NGC 6838). This data has allowed us to for the first time ever to obtain three dimensional velocity profiles for stars in the vicinity of centre of a globular cluster. Using the Near Infrared Imager with Adaptive Optics and a 3.8 year baseline for our astrometric study we have resolved the internal proper motion dispersion. The proper motion dispersion is found to be 179±17 µ year⁻¹, we have put a strict limit to the size of any central Intermediate Mass Black Hole at ~150 solar masses at 90% confidence, additionally we find no evidence of core anisotropy. Using our GMOS Integrated Field Unit spectroscopic data we have obtained a radial velocity dispersion of 3.54±0.64 km s⁻¹. Combining our proper motion and radial velocity dispersions we find the geometric distance to the cluster to be 4.1±1.2 kpc. We then compare our geometric distance to a distance found from fitting stellar evolution models. We have developed a new technique for fitting models, using this technique we find the stellar evolution model distance to be 3.9±0.2 kpc. We then discuss how this technique can easily be applied to other clusters in any future work.

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