Optical spectroscopy of the candidate luminous white dwarf in the young Large Magellanic Cloud cluster NGC 1818

An optical spectrum of the Elson et al. candidate luminous white dwarf in t he young LMC cluster NGC 1818 shows conclusively that it is not a degenerat e star. A model atmosphere fit gives T-eff approximate to 31 500 K and log g approximate to 4.4, typical of a normal main-sequence B star. However, if it is a true LMC member then the star is underluminous by almost 3 mag. It s position in the cluster colour-magnitude diagram also rules out the possi bility that this is an ordinary B star. The luminosity is, however, consist ent with a similar to 0.5-M. post-asymptotic giant branch or post-extended horizontal branch object, although if it has evolved via single-star evolut ion from a high-mass (7.6-9.0 M.) progenitor then we might expect it to hav e a much higher mass, similar to 0.9 M.. Alternatively, it may have evolved in a close binary. In this case the object offers no implications for the maximum mass for white dwarf progenitors, or the initial-final mass relatio n. Finally, we suggest that it could in fact be an evolved member of the LM C disc, and merely projected by chance on to NGC 1818. Spectroscopically, t hough, we cannot distinguish between these evolutionary states without high er resolution (echelle) data.