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D. Soderblom (STScI)
The TW Hydrae Association is a grouping of more than a dozen pre-main sequence low-mass stars. The brightest member is HD 98800, itself a quadruple system. HD 98800 is bright enough to have been included in the Hipparcos Input Catalogue, and so a good parallax is available. The multiplicity of HD 98800 complicates deconvolving the relevant parameters of individual stars to place them in an H-R diagram, although having more than one component also constrains fits to the points.
HD 98800 is about 10 to 20 Myr old. The limitations on defining this age more precisely will be presented, as will corroborating evidence from other TW Hya members. How did this meager group of pre-main sequence stars form and find its way to the solar neighborhood? Some scenarios that work, and some that don't, will be shown.
This work has been supported by grants from NASA Headquarters for the analysis of Hipparcos data, and from STScI for HST data analysis.