THE VERY RED HALO OF THE CD GALAXY IN A-3284

We present deep CCD surface photometry in the Gunn g, r, i system and spectroscopy of the cD galaxy at the centre of the cluster A 3284 at z = 0.15. The brightness profile of the galaxy has been tracked up to 4 0 arcsec (142 kpc) from the centre, and down to 26 mag/arcsec(2). The core and halo components in the galaxy have been singled out deriving geometrical parameters of the fitting isophotes as well as magnitudes and colours. The spectral properties of the galaxy core indicate a ste llar population super metal-rich with [Fe/H] = +0.5. The cD halo is cl early dominant at 45 kpc from the galactic centre and has exceedingly red colours (g - r = 1.03, g - i = 1.82), about 0.7 mag redder than th e core g - i. A match with the models for evolutionary population synt hesis by Buzzoni (1989) shows that the hare is consistent with a popul ation of unevolved M-dwarf stars lower than 0.7 Mo.. The M/L ratio in B for the halo is estimated to range between 50 and 200 implying a tot al mass for the cD galaxy of 1.6-3.1 10(13) M. and total B luminosity of 6.0 10(11) L..