Preliminary Analysis of an Ultraviolet Hubble Space Telescope Faint Object Camera Image of the Center of M31
Boksenberg, A.; Barbieri, C.; Weigelt, G.; Nota, A.; Crane, P.; Baxter, D.; Sparks, W. B.; Albrecht, R.; Blades, J. C.; Deharveng, J. M.; Disney, M. J.; Jakobsen, P.; Kamperman, T. M.; King, I. R.; Macchetto, F.; Mackay, C. D.; Paresce, F.; Greenfield, P.; Jedrzejewski, R.; Stanford, S. A.
United States, France, Netherlands, Germany, Italy, United Kingdom
Abstract
A 5161 s exposure was taken with the FOC on the central 44" of M31, through a filter centered at 1750 A. Much of the light is redleak from visible wavelengths, but nearly half of it is genuine UV. The image shows the same central peak found earlier by Stratoscope, with a somewhat steeper dropoff outside that peak. More than 100 individual objects are seen, some pointlike and some slightly extended. We identify them as post-asymptotic giant branch stars, some of them surrounded by a contribution from their accompanying planetary nebulae. These objects contribute almost a fifth of the total UV light, but fall far short of accounting for all of it. We suggest that the remainder may result from the corresponding evolutionary tracks in a population more metal-rich than solar.