CCD IMAGING OF NGC-4861 - IONIZED-GAS PROPERTIES AND STELLAR FORMATION

This work undertakes the study of the galaxy NGC 4861, using imaging c entered at the strong lines Ha, HP, [O III] lambda 5007 and nearby con tinua. Integrated, absolute fluxes of 28 H II regions, and the region known as the bright knot, have been measured showing correlations betw een the equivalent width of HP and the excitation index log([O III]/H beta). An excitation gradient has been detected along the chain of H I I regions extending northwards from the bright knot, which is unusual for irregular galaxies like NGC 4861. We suggest that this gradient is due to different stages of evolution, or ages, of the H II regions. T he continuum fluxes of eight emissionless associations and the continu um colors of the companion galaxy IC 3961 have also been measured, and the presence of ionized gas cannot be detected. The age and mass of t he stellar population and ionizing stars of the bright knot were subse quently estimated. It was also verified that this region is the most i mportant burst of star formation in NGC 4861.