Near-IR photometry of asymptotic giant branch stars in the dwarf elliptical galaxy NGC 185

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: 13 January 2005
Accepted: 4 March 2005

Abstract

J, H and K' images obtained with the Canada-France-Hawaii Telescope were used to investigate the stellar contents of the asymptotic giant branch (AGB) in the dwarf elliptical galaxy NGC 185. The bright parts of and color-magnitude diagrams consist of a group of bright blue stars, a dominant population of M-giants and a red C star population. There were 73 C stars with a mean magnitude of , corresponding to , and mean colors of and . The number ratio of C stars to M-giants was estimated to be without any radial gradient from the center of NGC 185. The and  color distributions of AGB stars showed an M-giant peak and blue and red tails, where the latter two correspond to AGB stars younger than those along M-giant peak and C stars. The bolometric luminosity functions of M-giants and C stars indicate that the M-giant AGB sequence has terminated at , while the most luminous C star has . The bolometric luminosity function of C stars in NGC 185 is very similar to that of recent literature values derived from Vi band photometry. The logarithmic slope of the luminosity function for bright M-giant stars was estimated to be in K band. Theoretical isochrone models, compared with the observed near-infrared photometric properties of AGB stars, indicate that star formation in NGC 185 has a wide range of ages with possibly two different epochs of star formation.