Toward a long-term phase-connected ephemeris for the unique X-ray binary HD49798

HD 49798 is a unique Xray binary composed of a 13.2 s pulsator, most likely thefastestrotating massive white dwarf (1.28+/0.05 solar masses), orbiting thebrightest subdwarf of O spectral type. We obtained a phaseconnected timingsolution, that should now be extended over a longer time period to unveil thesmall variations in the spin period expected in this system. Their study willallow us to unambiguously confirm the nature of the compact object, to shedlight on the accretion flow geometry and on the magnetic field intensity. Thisis an updated version of a similar proposal accepted in C priority in AO12. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]