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

A. Kang; Y.-J. Sohn; J. Rhee; M. Shin; M.-S. Chun; Ho-Il Kim

doi:10.1051/0004-6361:20052692

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Volume 437 / No 1 (July I 2005)

A&A, 437 1 (2005) 61-68

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Issue		A&A Volume 437, Number 1, July I 2005


Page(s)		61 - 68
Section		Extragalactic astronomy
DOI		https://doi.org/10.1051/0004-6361:20052692
Published online		10 June 2005

A&A 437, 61-68 (2005)

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

A. Kang¹^,2, Y.-J. Sohn¹^,2, J. Rhee¹^,2, M. Shin¹, M.-S. Chun¹ and Ho-Il Kim³

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 $(K, J-K)$ and $(K, H-K)$ 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 $\langle K\rangle = 16.26\pm0.38$ , corresponding to $\langle M_K\rangle = -7.93$ , and mean colors of $\langle (J-K)_0\rangle = 2.253$ and $\langle (H-K)_0\rangle = 0.865$ . The number ratio of C stars to M-giants was estimated to be $0.11\pm0.04$ without any radial gradient from the center of NGC 185. The $(J-K)$ and $(H-K)$ 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 $M_{\rm bol} = -6.2$ , while the most luminous C star has $M_{\rm bol} = -5.5$ . 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 $0.83\pm0.02$ 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. 

Key words: galaxies: individual: NGC 185 / galaxies: stellar content / stars: AGB and post-AGB

© ESO, 2005

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