Aims. We investigated the photometric properties of asymptotic giant branch (AGB) stars of the dwarf irregular galaxy IC 1613 and its metallicity. Methods. We used near-infrared JHK s photometric data obtained with the WIRCam array on Canada-France-Hawaii Telescope (CFHT). The optical gi imaging data of a previous study were cross-matched with ours to distinguish the stellar populations in the galaxy and to select the AGB stars. We also separated the C stars from the M-giant stars in the JHK s color−color diagram. Results. We identified 140 C stars and 306 M-giant stars in IC 1613. The (J − K s ) color histogram of AGB stars shows the main peak of M-giant stars and the red tail of C stars. The broad color distribution of M-giant stars and the isochrones in the color magnitude diagram indicate that IC 1613 has a wide range of intermediate-age stars. We also know that most C stars were formed over the past 2−8 Gyr according the M bol -age relation. The C/M ratio of 0.46 ± 0.05 was estimated and [Fe/H] abundance of −1.23 ± 0.06 was derived from the C/M ratio. Radial distributions of C/M ratio and metallicity show the shallow trend of the negative metallicity gradient from the center. The local C/M ratio also indicates that the HI cavity has higher C/M values than the bright HI spot and HI gas region. However, the low [Fe/H] value near the central region of the galaxy is likely to be caused by the change in age of the dominant stellar population according to the radial distance, not the real metallicity variation. It might also be that relatively younger and metal-rich C stars are concentrated in the center of the galaxy, while the M-giant stars were homogeneously distributed from the center to the borders of the galaxy.

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.

The JHK S magnitudes of the red giant branch tip (TRGB) and the distance moduli of the nearby dwarf irregular galaxy IC 1613 have been determined from the nearinfrared luminosity functions (LFs) of the resolved stars in the galaxy. Applying a Savitzky-Golay filtering, we derived the second derivatives of the LFs, and estimated the apparent magnitudes of the TRGB as m J = 19.1, m H = 18.4, and m Ks = 18.0. The mean values of the theoretical absolute magnitudes of the TRGB were measured by using the Yonsei-Yale isochrones with a metallicity range of −2.1 < [Fe/H] < −0.5 and age of 12 Gyr. The derived values of near-infrared TRGB distance moduli for IC 1613 are (m − M ) = 24.12 ± 0.25, 24.20 ± 0.44, and 24.00 ± 0.52 for J, H, and K S bands, respectively.

We have used the near-infrared JHK S photometric data of resolved stars in a nearby dwarf elliptical galaxy NGC 205 to determine the magnitudes of the red giant branch tip (TRGB). By applying Savitzky-Golay filter to the observed luminosity functions (LFs) in each band, we derived the second derivatives of the LFs so as to determine the magnitudes of the TRGB. Absolute magnitudes of the TRGB in JHK S bands were measured from the Yonsei-Yale isochrones. By comparing the determined apparent magnitudes and the theoretical absolute magnitudes of the TRGB, we estimated the distance moduli of NGC 205 to be (m − M ) = 24.10 ± 0.08, 24.08 ± 0.12 and 24.14 ± 0.14 in J, H, and K S bands, respectively.