UV abundances in HE0107-5240

Abstract

We have determined the CNO abundances from OH, CH and NH lines in the VLT/UVES UV spectra of HE0107-5240 and CD-38 245 together with the abundances of several metal species, including FeII, whose lines were not detected in blue spectra. The UV abundance analyses support those determined from the blue spectra, in particular the abundance from the FeII lines is in good agreement with the Fe abundance derived from the Fe I lines. It seems unlikely that the large overabundances of CNO have been produced in a medium-mass AGB star which now evolved to a white dwarf. The oxygen abundance is consistent with the predictions of Umeda & Nomoto (2003, 2005), who proposed that HE0107-5240 has formed from a gas cloud which has been enriched by the yields of a $\approx 25$ solar mass Population III star exploding as a supernova of low explosion energy E${=} 3.10^{50}$ erg with mixing and fallback. The odd-even effect predicted in the original models are not evident in the Sc and Co abundances of HE0107-5240, which are better fitted by the low density variant progenitor model.