Based on the observations collected at the MMT, which is a joint facility of the Smithsonian Institution and the University of Arizona. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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http://cxc.harvard.edu/ciao/

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... COLDEN

http://cxc.harvard.edu/toolkit/colden.jsp

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... tools

http://www.eso.org/~jliske/vpguess/, http://www.ast.cam.ac.uk/~rfc/vpfit.html

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