INFRARED-EMISSION AND MASS-LOSS FROM EVOLVED STARS IN ELLIPTIC GALAXIES

Small aperture 10.2 mum measurements of normal elliptical galaxies show that for almost all of these galaxies the 12 mum emission seen by IRAS is extended on the scale of the galaxy. NGC 1052 and NGC 3998 are exceptions to this; much of their 10-12 mum emission comes from the inner regions of the galaxies and may be associated with their active nuclei, as is the case for many radio galaxies. The distribution of the infrared light and the infrared colors of elliptical galaxies suggest that the most plausible source of the 12 mum emission is photospheric and circumstellar emission from cool evolved red giant stars. The 12 mum emission is well in excess of that expected from photospheric emission alone; about 40% of it probably comes from circumstellar dust. The 12 and 2.2 mum measurements are used to derive a total mass-loss rate of 0.0021 L2.2/L. M. Gyr-1 for the evolved giant stars in elliptical galaxies, in excellent agreement with earlier and completely independent estimates based on optical luminosities and stellar evolutionary considerations.