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SDSSJ212531.92-010745.9 is the first known PG1159 star in a close binary witha late main sequence companion allowing a dynamical mass determination. Thesystem shows flux variations with a peak-to-peak amplitude of about 0.7 mag anda period of about 6.96h. In August 2007, 13 spectra of SDSSJ212531.92-010745.9covering the full orbital phase range were taken at the TWIN 3.5m telescope atthe Calar Alto Observatory (Alm\'{e}ria, Spain). These confirm the typicalPG1159 features seen in the SDSS discovery spectrum, together with the Balmerseries of hydrogen in emission (plus other emission lines), interpreted assignature of the companion's irradiated side. A radial velocity curve wasobtained for both components. Using co-added radial-velocity-corrected spectra,the spectral analysis of the PG1159 star is being refined.  The system's lightcurve, obtained during three seasons of photometry with theG\"ottingen 50cm and T\"ubingen 80cm telescopes, was fitted with both theNIGHTFALL and PHOEBE binary simulation programs. An accurate mass determinationof the PG1159 component from the radial velocity measurements requires to firstderive the inclination, which requires light curve modelling and yields furtherconstraints on radii, effective temperature and separation of the system'scomponents. From the analysis of all data available so far, we present thepossible mass range for the PG1159 component of SDSSJ212531.92-010745.9.

Dynamic masses for the close PG1159 binary SDSSJ212531.92-010745.9