An X-ray and optical study of the cluster A33

We report the rst detailed X-ray and opti- cal observations of the medium-distant cluster A33 ob- tained with the Beppo-SAX satellite and with the UH 2.2 m and Keck II telescopes at Mauna Kea. The in- formation deduced from X-ray and optical imaging and spectroscopic data allowed us to identify the X-ray source 1SAXJ0027.2 1930 as the X-ray counterpart of the A33 cluster. The faint, F2 10 keV 2: 41 0 13 erg s 1 cm 2 , X-ray source 1SAXJ0027.2 1930, 2 arcmin away from the optical position of the cluster as given in the Abell cat- alogue, is identied with the central region of A33. Based on six cluster galaxy redshifts, we determine the redshift of A33, z =0 :2409; this is lower than the value derived by Leir & Van Den Bergh (1977). The source X-ray luminos- ity, L2 10 keV =7 : 71 0 43 erg s 1 cm 2 , and intracluster gas temperature, T =2 :9 keV, make this cluster inter- esting for cosmological studies of the cluster LX T re- lation at intermediate redshifts. Two other X-ray sources in the A33 eld are identied. An AGN at z =0 :2274, and an M-type star, whose emissions are blended to form an extended X-ray emission 4 arcmin north of the A33 cluster. A third possibly point-like X-ray source detected 3 arcmin north-west of A33 lies close to a spiral galaxy at z =0 :2863 and to an elliptical galaxy at the same red- shift as the cluster.