Near-infrared properties of asymptotic giant branch stars in nearby dwarf elliptical galaxy NGC 205⋆,⋆⋆
1 Department of Astronomy, Yonsei University, 120-749 Seoul, Korea
2 Yonsei University Observatory, 120-749 Seoul, Korea
3 Korea Astronomy and Space Science Institute, 305-348 Daejeon, Korea
4 CEOU, Department of Physics and Astronomy, Seoul National University, 151-742 Seoul, Korea
Received: 14 February 2012
Accepted: 10 May 2012
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 JHKs color − magnitude diagrams, and separated the C stars from M-giant stars in the JHKs color − color diagram.
Results. We identified 1,550 C stars in NGC 205 with a mean absolute magnitude of ⟨ MKs ⟩ = −7.49 ± 0.54, and colors of ⟨ (J − Ks)0 ⟩ = 1.81 ± 0.41 and ⟨ (H − Ks)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 − Ks) 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 (tyr) ~ 9.0−9.7. The logarithmic slope of the MKs 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 MKs 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 Mbol = −6.0 mag, and that for C stars spans −5.6 < Mbol < −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 Mbol = −4.24 ± 0.55, which is consistent with our results for dwarf elliptical galaxies NGC 147 and NGC 185.
Key words: galaxies: individual: NGC 205 / galaxies: stellar content / stars: AGB and post-AGB
Based on observations carried out at the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France, and the University of Hawaii.
Calibrated photometry is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/543/A35
© ESO, 2012