Near-IR photometry of asymptotic giant branch stars in the dwarf elliptical galaxy NGC 147

¹ Department of Astronomy, Yonsei University, Seoul 120-749, Korea e-mail: sohnyj@yonsei.ac.kr; breeze82@galaxy.yonsei.ac.kr
² Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea
³ Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea

Received: 7 June 2005
Accepted: 31 July 2005

Abstract

Near-infrared and K' images were used to investigate the stellar contents of the asymptotic giant branch (AGB) population in the nearby dwarf elliptical galaxy NGC 147. The obtained and color–magnitude diagrams contain stars of AGB and red giant branch populations, where the former consists of a group of bright blue stars, a dominant population of M giant and a red C star population. We identified 91 AGB C stars in NGC 147 with the mean absolute magnitude and colors of , and . The estimated number ratio of C stars to M giant stars (C/M) is . The estimated local C/M ratios of for the inner region () and for the outer region () indicate a weak radial gradient. The mean bolometric magnitude of 91 C stars in NGC 147 is . The bolometric luminosity function of M giant stars in NGC 147 extends up to  mag, and that of only C stars spans . The color histograms of AGB stars in and show a main peak containing M giant stars, a red tail containing C stars with a weak excess, and a blue excess possibly due to bright blue foreground stars and AGB stars younger than M giants. The comparison of the theoretical isochrone models with the color distribution and the brightness of AGB stars indicates that most of the bright M giants in NGC 147 were formed at log  with a range of . Ages of the majority of M giant stars in NGC 147 are similar to those of younger M giant stars in its companion NGC 185, while their formation occurred more recently than the older M giant stars in NGC 185 by ~2 Gyr.