The stellar population of the nucleus of M 33 from an analysis of itslambda-lambda 1200-3000 A spectrum.

Abstract

The λλ1200 - 3000 Å spectrum of the nucleus of M33 is used in conjunction with U, B, V photometry as input to a linear programming method to determine the stellar population of the system. No astrophysical constraints but modifications in the stellar library (which includes Population II objects) were used to explore different evolutionary histories of star formation in the nucleus. A multigeneration model, where a young component (age ≡10⁷years) and an old one (age ≡5×10⁹ years) are superimposed, gives the best fit to the data and is favoured by the results at other wavelengths as well. The effect of reddening on the modelling and the interpretation of the nuclear X-ray source are briefly discussed.