The fast-spinning ultra-massive white dwarf companion of HD 49798

HD49798/RXJ06484418 is an Xray binary with unique properties: the primary staris the brightest known subdwarf of early spectral type, while the secondary isthe fastest rotating (P13.2 s) and one of the most massive (M>1.2 Msun) whitedwarfs currently known. We propose a followup study to better understand theproperties of the Xray emission and derive tighter constraints on the masses ofthis interesting postcommon envelope binary. In addition, observations near thetime of the eclipse will provide for the first time information on the stellarwind properties of a hot subdwarf. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]