16708

The bright comma nearby star V723 Mon has a 3 Solar mass dark companion comma most easily explained as a mass gap black hole. There is no optical spectral evidence for a stellar companion comma nor are there continuum eclipses comma but there is evidence of a non-stellar comma blue d_commaveiling.. light and eclipses of the Balmer lines. Extraordinary claims require extraordinary evidence comma and so it is important to better characterize the excess UV emission. Because all but one (UVM2) of the Swift UV filters have red leaks comma the shape of the UV spectral energy distribution (SED) cannot be measured with Swift in the presence of V723 Mon. A rising UV SED would strongly suggest the presence of a hot stellar companion. More generally comma the UV emission is not dominated by the red giant and so is the best place to search for spectral features from any stellar companion. If it is not stellar emission comma the UV is also an important probe of the origin of the claimed d_commaveiling.. light source. These questions are easily addressed with two one orbit STIS-CCD-G230LB spectra comma one in eclipse and one out of eclipse.