The Compact UV Nucleus of M33

The most luminous X-ray source in the Local Group is associated with thenucleus of M33. This source, M33 X-8, appears modulated by ~20% over a ~106 dayperiod, making it unlikely that the combined emission from unresolved sourcescould explain the otherwise persistent ~1e39 erg/s X-ray flux (Dubus et al.1997, Hernquist et al. 1991). We present here high resolution UV imaging of thenucleus with the Planetary Camera of the HST undertaken in order to search forthe counterpart to X-8. The nucleus is bluer and more compact than at longerwavelength images but it is still extended with half of its 3e38 erg/s UVluminosity coming from the inner 0.14". We cannot distinguish between aconcentrated blue population and emission from a single object.