HST WFPC2 OBSERVATION OF THE CORE OF M-3 - BLUE OBJECTS AND THE POSITION OF THE RADIO-SOURCE/

HST/WFPC2 images of the central part of the globular cluster M 3 (NGC 5272) in UV (F255W), U (F336W), V (F555W) and I (F814W) are used to se arch for faint blue stars down to an UV magnitude slightly below the t urnoff level. Three low-luminosity blue stars are found in the PC 1 fi eld of view, two are new detections. All are within similar to 10 '' f rom the cluster centre. Two are likely horizontal branch stars on the extreme blue extension which turns out very scarce in the core of this cluster. The third object has a position in the UV color-magnitude di agram consistent with the cataclysmic variables region; changes in its magnitude during the limited period of observation provide marginal i ndication of variability. One of the very few known non-pulsating radi o sources, located in the direction of the centre, is accurately posit ioned. Its position does not match any of the low luminosity blue star s by similar to 7 ''. In turn, the error box of the radio source posit ion contains two interesting objects: a bright horizontal branch star and a bright blue straggler, both are within similar to 1 ''. NO other object in the vicinity of the radio source shows any photometric sign ature of an unusual cluster object or of an extragalactic source. Vari ability of some candidates (RR Lyrae and BSS) has been confirmed; new variable candidates of both types have also been found.