Using the Near Infrared Camera and Multi-Object Spectrometer ( NICMOS ) on board the Hubble Space Telescope , we have obtained F 110 W ( \sim J ) and F 160 W ( \sim H ) images of three fields in NGC3379 , a nearby normal giant elliptical galaxy .
These images resolve individual red giant stars , yielding the first accurate color-magnitude diagrams for a normal luminous elliptical .
The photometry reaches \sim 1 magnitude below the red giant branch tip with errors of \lesssim 0.2 mags in F 110 W - F 160 W .
A strong break in the luminosity function at F 160 W = 23.68 \pm 0.06 is identified as the tip of the red giant branch ( RGB ) ; comparison with theoretical isochrones implies a distance of 10.8 \pm 0.6 Mpc , in good agreement with a number of previous estimates using various techniques .
The mean metallicity is close to solar , but there is an appreciable spread in abundance , from at least as metal poor as [ Fe/H ] \approx - 1.5 to as high as +0.8 .
There is a significant population of stars brighter than the RGB tip by up to \sim 1 magnitude .
The observations of each field were split over two epochs , separated by 2 - 3 months , allowing the identification of candidate long period variables ; at least 40 \% of the stars brighter than the RGB tip are variable .
Lacking period determinations , the exact nature of these variables remains uncertain , but the bright AGB stars and variables are similar to those found in metal rich globular clusters and are not luminous enough to imply an intermediate age population .
All of the evidence points to a stellar population in NGC3379 which is very similar to the bulge of the Milky Way , or an assortment of Galactic globular clusters covering a large metallicity spread .