Near-infrared properties of asymptotic giant branch stars in nearby dwarf elliptical galaxy NGC

M. Y. Jung, J. Ko, J. W. Kim, S. H. Chun, H. I. Kim, Y. J. Sohn

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Abstract

Aims. We investigated the distribution of resolved asymptotic giant branch (AGB) stars over a much larger area than covered by previous near-infrared studies in the nearby dwarf elliptical galaxy NGC 205. Methods. Using data obtained with the WIRCam near-infrared imager of the CFHT, we selected the AGB stars in the JHK s color-magnitude diagrams, and separated the C stars from M-giant stars in the JHK s color-color diagram. Results. We identified 1,550 C stars in NGC 205 with a mean absolute magnitude of M Ks=-7.49 ± 0.54, and colors of (J-K s) 0 = 1.81 ± 0.41 and (H-K s) 0 = 0.76 ± 0.24. The ratio of C stars to M-giant stars was estimated to be 0.15 ± 0.01 in NGC 205, and the local C/M ratios for the southern region are somewhat lower than those for the northern region. The (J-K s) color distributions of AGB stars contain the main peak of the M-giant stars and the red tail of the C stars. A comparison of the theoretical isochrone models with the observed color distribution indicates that most of the bright M-giant stars in NGC 205 were formed at log (t yr) ∼ 9.0-9.7. The logarithmic slope of the M Ks luminosity function for M-giant stars was estimated to be 0.84 ± 0.01, which is comparable with dwarf elliptical galaxies NGC 147 and NGC 185. Furthermore, we found that the logarithmic slopes of the M Ks luminosity function for C and M-giant stars are different to places, implying a different star formation history within NGC 205. The bolometric luminosity function for M-giant stars extends to M bol =-6.0 mag, and that for C stars spans-5.6 < M bol <-3.0. The bolometric luminosity function of C stars is unlikely to be a Gaussian distribution and the mean bolometric magnitude of C stars is estimated to be M bol =-4.24 ± 0.55, which is consistent with our results for dwarf elliptical galaxies NGC 147 and NGC 185.

Original languageEnglish
Article numberA35
JournalAstronomy and Astrophysics
Volume543
DOIs
Publication statusPublished - 2012 Jun 29

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All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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