Long-term phase-connected timing of the unique X-ray binary HD49798

HD49798 is the only known Xray binary with a hot subdwarf companion. Thecompact object (a white dwarf or a neutron star) has a spin period of 13 s andhas been steadily spinning up at 2x10^{15} s/s for the last 20 years.Independently of its NS or WD nature, this spinup is difficult to explain withthe angular momentum that accretion can supply. An alternative explanationimplies the presence of a young WD, still in the contracting phase. A newobservation must be secured as soon as possible in order to extend the phaseconnected timing solution of this unique binary and shed light on thenature ofthe compact object. This fulfil proposal was accepted in AO17 (C priority) butnot executed. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]