SUBARCSEC STRUCTURES IN THE DOUBLE NUCLEUS OF NGC-6240 DISCLOSED WITHHST AT 370, 430 AND 500 NM

We present an analysis of three medium band width (FWHM similar to 400 - 450 Angstrom) images of the nuclear region of NGC 6240 taken with t he pre-COSTAR Faint Object Camera (FOG) on board of the Hubble Space T elescope. The first filter band comprises the [OII]lambda 3727 doublet , the second measures the blue continuum around 4400 Angstrom and the third includes H beta + [OIII]lambda lambda 4959, 5007. The images sho w that the apparent two galactic nuclei B (north) and A (south) identi fied from the ground consist of compact subtructures on the tenth-arcs ec scale plus faint extended emission on the arcsec scale. Within a di ameter of 0.'' 26 (similar to 120 pc), most compact features exhibit a summed line luminosity L([OIII] + H beta) in the range 10(39)-10(40) erg s(-1) which is comparable to that of giant HII regions. Although t he data are not complete enough for a direct decomposition into line a nd continuum flux, probable solutions yield a LINER like [OII]/[OIII]/ H beta line ratio for the northern compact subcomponent B1. In the sou thern nucleus A the faint subcomponents A2 and A3 can be classified as LINER like if they are more strongly reddened than B1 or as HII-regio n like if not. The brightest southern compact component Al, however, e xhibits line ratios that are typical of (i) a Seyfert galaxy or (ii) a high-excitation HII region. This leads to the interesting alternative that there is either (i) a hidden AGN (which is in accord with recent ASCA observations) or (ii) a hidden cluster of young massive stars. T he second possibility would imply localized ongoing star formation wit hin an environment whose visible light is dominated by radiation from older stellar populations. However, considering recent models for fast autoionizing shocks computed by Dopita & Sutherland (1995), Al might also represent a shock-plus-precursor region.