  We have determined the oxygen abundance of HE0107-5240 from UV-OH lines
detected in VLT/UVES spectra. Using a plane-parallel LTE model atmosphere, we
derive [O/Fe] = +2.4, and a similar analysis of CD -38 245 yields [O/Fe] =
+1.0. We estimate systematic errors due to 3D effects to be in the order of 0.3
to 0.4 dex. That is, our derived O abundances are likely overestimates: effects
from thermal inhomogeneities due to convection may require that the abundances
should be reduced by 0.3-0.4 dex or even more. Radial velocity data for
HE0107-5240 based on high-resolution spectra show that over a time span of 373
days the radial velocity was constant at 44.5 km/s, with a 1 sigma scatter of
the measurements of 0.5 km/s. However, it can not yet be ruled out that
HE0107-5240 is a very long period and/or low amplitude binary. These results
provide new constraints on scenarios for the origin of the abundance pattern of
HE0107-5240. In particular, it seems unlikely that the large overabundances of
CNO have been produced in a medium-mass AGB star which later evolved to a white
dwarf. The oxygen abundance of HE0107-5240 is significantly smaller than the
prediction of Umeda & Nomoto (2003) from calculated yields of a ~25 solar mass
Population III star exploding as a supernova of low explosion energy (E_exp = 3
x 10^50 erg) with mixing and fallback. The scenario of Limongi et al. (2003),
involving two Population III supernovae, predicts an oxygen abundance of [O/Fe]
= +4.1 for HE0107-5240, in strong contradiction with the observed value. In
conclusion, none of the above mentioned scenarios, in their present
realizations, can satisfactorly explain the abundance pattern of HE0107-5240.
