SPECTROSCOPIC ANALYSIS OF EARLY-TYPE STARS IN YOUNG STELLAR GROUPS .1. DIFFERENTIAL ANALYSIS OF THE B1V STARS IN NGC-2244

We explore the potential of analysing fast rotating early-type stars d ifferentially with respect to templates derived from a slowly rotating star of the same spectral type. The analysis is successfully applied to the normal B 1 V stars in NGC 2244, which have projected rotational velocities ranging from 22 to 260 km s(-1). A classical non-LTE analy sis of the slow rotator #201 results in chemical abundances similar to those of early B-type stars in the field and in Orion. We argue that a differential analysis of the fast rotators relative to a broadened t emplate derive;I from #201 can still reveal abundance differences of g reater than or similar to 0.2 dex, but no evidence was found for diffe rences in metal composition at this level. A differential analysis of H and He line profiles reveals the need to further explore rotation mo dels. Neither the classical approach to stellar rotation, nor the publ ished models that include the influence of rotation on the star's atmo sphere can bring the profiles of the slow rotator into complete agreem ent with those of the fast rotators. An attempt to extend the analysis to a Be star failed. The Be spectrum is described qualitatively and q uantitative measurements are made for the emission in the core of the Balmer lines.