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Session 46 - Old Stellar Populations Beyond The Milky Way.
Display session, Wednesday, June 11
South Main Hall,
We present photometry of far-UV (1500 Åwide-field images of six E/SO galaxies taken with the Ultraviolet Imaging Telescope during the Astro-2 mission. In three cases, the radial FUV surface brightness profiles are more consistent with an exponential decline than a de Vaucouleurs function. As in earlier studies, however, there is no evidence that massive hot stars contribute to the FUV light, and the FUV axial ratios and isophote orientations are similar to those at optical wavelengths. The systems span a wide range of central FUV--B color. There is also a wide range of radial FUV--B color gradients. In two cases, the color reddens with increasing radius (i.e. FUV light is more concentrated to the galaxy center than is B band light); in three cases, there is little gradient. In M32, there is a strong reversed gradient, first reported from Astro-1 data, in which FUV--B becomes bluer with radius. We find no correlation between the FUV--B color gradients and internal metallicity gradients based on Mg absorption features. We conclude that metallicity is not the sole parameter controlling the ``UV upturn component'' in old populations.
Program listing for Wednesday