The peculiar cluster HS 327 in the Large Magellanic Cloud: Can OH/IR starsand carbon stars be twins?

The obscured OH/IR star IRAS 05298-6957 in the LMC was recently noticed to be member of the small double cluster HS 327 that also contains a carbon st ar (van Loon, et al. 1998, A&A, 329, 169). Hence they are coeval and have ( nearly) the same progenitor mass, which can only be understood if Hot Botto m Burning (HBB) has prevented IRAS 05298-6957 from being a carbon star. We present extensive visual and near-IR photometric data for >10(4) stars in a nd around HS 327, and spectroscopic data for some of the brightest AGE star s amongst these. Colour-magnitude diagrams are used to estimate the age for the cluster and its members, and luminosities are derived for the stars fo r which spectra have been obtained. The age for IRAS 05298-6957 and the car bon star is estimated to be similar to 200 Myr. This corresponds to a Main- Sequence progenitor mass similar to4.0 M-circle dot.- the first direct meas urement of the lower mass threshold for HBB. This agrees with stellar evolu tion models that, however, fail to reproduce the low luminosity of the carb on star.