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The Central Star of A63 – UU Sge Don Pollacco (Queens University Belfast, UK), Ralf Napiwotzki (Banberg, Germany), Steve Bell (HMNAO, UK) Katrina Exter (Queens University Belfast, UK).

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  1. The Central Star of A63 – UU SgeDon Pollacco (Queens University Belfast, UK), Ralf Napiwotzki (Banberg, Germany), Steve Bell (HMNAO, UK)Katrina Exter (Queens University Belfast, UK) UU Sge is unique amongst central star in that it is a totally eclipsing binary. Hence physical parameters for the components can be derived, in principle, with great accuracy. The morphology of A63 is extreme, exhibiting an aspect ratio of some 7:1! This result is consistent with the light curve solutions derived using a 6000K secondary – as derived from spectra obtained during the brief (but faint) total eclipse. These results imply a distance of 2.4 kpc (±20%). The spectra here were obtained near phase 0.5 (top) and around 0.0 (middle). The difference shows the irradiated spectrum (bottom). Double peaked hydrogen lines and narrow forbidden lines arise high in the atmosphere of the secondary star. Model atmosphere fits to the spectrum of the sdO star (near phase 0) require Teff~70000K. At other phases emission lines from the irradiated phase contaminate absorption lines and in the case of OIV and CIV lines, fill them in completely!

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