Isophotometry of elliptical galaxies.

Abstract

Isophotal contours have been traced directly for several regular galaxies with the Michigan isophotometer. The plate material includes short and long exposures with the Curtis Schmidt telescope, in blue and red light, with each plate standardized in a tube sensitometer. Tracings were made at several orientations in order to minimize grain effects. So far the following preliminary results have been obtained. The study of a number of other smooth galaxies is being continued. I. The prototype E7 galaxy, NGC 3115, has been examined on both blue and red plates, and there is no conclusive evidence of any changes in color index throughout the system. The b/a ratios change markedly with distance from the nucleus, with a minimum value 0.29 at a = I `.0 and less flattened isophotes both interior and exterior to this point. These results are in general accord with those of Oort and de Vaucouleurs. Within the accuracy of the measures, a given contour has the same shape in blue and red light. 2. NGC 3377 (E~) and NGC 3379 (Eo) have fairly regular elliptical contours, with no obvious changes in the b/a values. 3. Isophotes were also derived for two very regular-appearing barred spirals in the same field, NGC 33~4 (SBa) and NGC 3412 (SBa). In each of these systems, the contours change from approximate circles near the center to highly elongated ellipses at low intensity levels, with a progressive twist in the position angle of the major axis. This work was supported by a Summer Faculty Research Fellowship of the University of Michigan. University of Michigan, A nn A rbor, Mich.