The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822

A. Kang, Y.J. J. Sohn, H.-I. Kim, J. Rhee, J.-W. Kim, N. Hwang, M. G. Lee, Y.-C. Kim, M.-S. Chun

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21 Citations (Scopus)


Images of {JHK} and {gi} obtained with the Canada-France-Hawaii Telescope are used to investigate the stellar contents of the resolved asymptotic giant branch (AGB) population in the area of 3.6 arcmin×6.3 arcmin on the central bar of the dwarf irregular galaxy NGC 6822. The upper envelope of near-infrared (J-K,K) and (H-K,K) color-magnitude diagrams (CMDs) shows four components of main-sequence stars, foreground stars, massive supergiants, and AGB stars. These components are also noticeable in the bright part of (g-i,g) CMD. We select AGB stars in NGC 6822 from the (g-K,g) CMD, which has a long spectral wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of < MK>=-7.60±0.50, and with mean colors of < (J-K)0>=1.77±0.41, and < (H-K)0>=0.75±0.28. The number ratio of C stars to M-giants (C/M) is estimated as 0.27±0.03, while the northern part of the bar has a somewhat lower C/M ratio than the southern part. The (J-K) and (H-K) color distributions of AGB stars contain a main peak of M-giant stars and a red tail of C stars. The broad color distributions for M-giants indicate that NGC 6822 has a wide range of intermediate ages with a peak at log(t_yr)˜9.0. The MK luminosity function (LF) for C stars in the central bar of NGC 6822 is likely to be a Gaussian distribution, while the LF of C stars in the southern part is slightly skewed to the brighter side than in northern part. The mean bolometric magnitude of 141 C stars in NGC 6822 is < M_bol>=-4.36±0.54. The bolometric LF for M-giants extends up to M_bol=-6.5, while the one for C stars spans -5.8
Original languageEnglish
Pages (from-to)717-727
JournalAstronomy and Astrophysics
Issue number3
Publication statusPublished - 1 Aug 2006
Externally publishedYes


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