Near-Infrared Color Evolution of LMC Clusters
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A&A 409, 479–484 (2003) Astronomy DOI: 10.1051/0004-6361:20031136 & c ESO 2003 Astrophysics Near-infrared color evolution of LMC clusters J.-M. Kyeong1, M.-J. Tseng2, and Y.-I. Byun3 1 Korea Astronomy Observatory, Taejon, 305-348, Korea 2 Institute of Astronomy, National Central University, Chung-Li, 32054, Taiwan, ROC 3 Yonsei University Observatory and Department of Astronomy, Yonsei University, Seoul, 120-749, Korea Received 5 May 2003 / Accepted 7 July 2003 Abstract. We present here the digital aperture photometry for 28 LMC clusters whose ages are between 5 Myr and 12 Gyr. This photometry is based on our imaging observations in JHK and contains integrated magnitudes and colors as a function of aperture radius. In contrast to optical colors, our near-infrared colors do not show any strong dependence on cluster ages. Key words. galaxies: photometry – galaxies: Magellanic Clouds – galaxies: star clusters – infrared: stars 1. Introduction Previous effort in near-infrared includes Persson et al. (1983, hereafter Persson83) and Ferraro et al. (1995). Star clusters of the Large Magellanic Cloud (LMC) provide ex- Persson83 studied the integrated light of 84 clusters in the cellent templates for studies of stellar populations in external Large and Small Magellanic Clouds using a single cell pho- galaxies. The LMC is close enough that star clusters within the toelectric aperture photometry. In contrast to the UV and opti- galaxy can be resolved into individual stars by high spatial res- cal clusters colors which vary smoothly with age, their infrared olution imaging from both ground and space based telescopes. integrated colors display a large scatter among a given SWB Their CMDs can be used for detailed age calibration. These star classification. They defined a group of IR enhanced clusters clusters are also populous enough that their integrated colors that belong to SWB groups IV–VI, i.e., in the intermediate-age are less sensitive to stochastic effects when compared to galac- with the very red J − K and H − K colors. This color excess is tic open clusters. Most importantly, unlike globular cluster in due to the existence of luminous carbon stars on the asymptotic our Galaxy, clusters in the LMC are known to cover wide range giant branch, which are responsible for as much as half of the of ages, making them ideal objects to investigate the integrated bolometric luminosity in the near-infrared. spectral behavior of simple stellar population as functions of both age and chemical composition. Ferraro et al. (1995) was the first who used a small, but Integrated photometry for LMC clusters had been studied two-dimensional InSb array for near-infrared observation of since van den Bergh & Hagen (1968), who performed UBV LMC clusters. With the classical and overshooting stellar evo- photoelectric aperture photometry. In 1980, Searle, Wilkinson lution theories, they investigated how red stars dominate the and Bagnuolo carried out an extensive program of uvgr aper- bolometric luminosity of a simple stellar population after its ture photometry, which resulted in a classification scheme early evolutionary stage. These red stars are considered to be of age-calibration with the reddening-free parameter Q(vgr) in phase transitions; asymptotic giant branch (AGB) and red and Q(ugr). This scheme is now called the SWB classification. giant branch (RGB) branch, in particular. Their overall result is Their work showed that the integrated colors appear to corre- consistent with the earlier work by Persson83. The age depen- late with cluster ages, and can be used as a primary age in- dent variation for V − K (substantially controlled by AGB and dicator. Elson & Fall (1985) translated the SWB classification RGB stars) shows a large scatter, which makes it almost useless into the UBV two-color diagram and also introduced a redden- for the purpose of age calibration as well as for the evolutionary ing independent parameter, s, which agrees with the SWB se- study of simple stellar populations. quence for 90% of clusters. Girardi et al. (1995) revised the Using a large format detector which enables more careful relation between the parameter s and cluster ages to consider background estimates and covers a larger cluster area, we aim the dispersion of observed colors due to stochastic effects and to collect a homogeneous data set for LMC clusters in the near- metallicity variation. infrared and re-examine the age dependence of integrated in- frared color. Send offprint requests to: J.-M. Kyeong, e-mail: [email protected] This paper is a part of a long term study to understand the Tables 2 and 3 and Fig. 2 are only available in electronic form at broad band color evolution of stellar systems with both simple http://www.edpsciences.org and more complex stellar populations. Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20031136 480 J.-M. Kyeong et al.: Near-infrared color evolution of LMC clusters Table 1. Basic properties of LMC clusters in our sample. NGC RA(J2000) Dec SWBa sb log tc [Fe/H]d E(B − V)e Dia. f Vg B − V g U − Bg 1651 04 37 32.1 −70 35 07 V 39 9.30 −0.37 0.11 62V 12.67 0.69 0.30 1711 04 50 37.2 −69 59 03 I 20 7.70 −0.57 0.16 60V 10.11 0.12 −0.37 1783 04 59 10.0 −65 59 14 V 37 9.00 −0.45 0.10 72V 10.93 0.62 0.23 1786 04 59 07.9 −67 44 38 VII 48 10.18 −1.87 0.12 60V 10.88 0.74 0.10 1806 05 02 13.2 −67 59 07 V 40 9.30 −0.23 0.12 88V 11.10 0.73 0.26 1818 05 04 14.8 −66 26 04 I 18 7.40 −0.4∼0.0 0.10 72V 9.70 0.18 −0.47 1831 05 06 15.6 −64 55 03 IVA 31 8.50 0.01 0.10 60V 11.18 0.34 0.13 1847 05 07 05.4 −68 58 41 I 21 7.42 −0.37 0.10 72V 11.06 0.20 −0.33 1850 05 08 45.8 −68 45 42 II 21 7.50 −0.12 0.15 50T 9.57 0.15 −0.27 1856 05 09 30.3 −69 08 05 IVA 30 8.12 −0.52 0.24 62V 10.06 0.34 0.07 1866 05 13 39.1 −65 27 56 III 27 8.12 −0.50 0.10 72V 9.73 0.25 −0.04 1868 05 14 35.4 −63 57 16 IVA 33 8.74 −0.50 0.07 62V 11.56 0.45 0.15 1967 05 26 44.3 −69 06 06 I 12 7.00 0.14 50T 10.83 0.05 −0.75 1978 05 28 44.3 −66 14 08 VI 45 9.70 −0.42 0.10 62V 10.70 0.78 0.23 1983 05 27 44.3 −68 59 03 I 13 6.90 0.09 45V 9.94 0.10 −0.76 1987 05 27 18.2 −70 44 05 IVB 35 8.80 0.12 62V 12.08 0.52 0.20 2004 05 30 40.3 −67 17 10 I 15 7.30 −0.56 0.06 72V 9.60 0.17 −0.68 2031 05 33 40.9 −70 59 06 III 27 8.20 −0.52 0.07† 72V 10.83 0.27 -0.05 2074 05 39 01.7 −69 29 51 0 10 6.60 0.07 150T 9.32 -0.16 −0.91 2100 05 42 07.8 −69 12 42 I 17 7.20 −0.32 0.24 60V 9.60 0.16 −0.56 2107 05 43 12.1 −70 38 24 IVA 32 8.60 0.19 60V 11.51 0.38 0.13 2134 05 51 56.7 −71 05 45 III 28 8.00 −1.0 0.10 60V 11.05 0.25 −0.02 2136 05 52 57.7 −69 29 24 III 26 8.00 −0.55 0.10 60V 10.54 0.28 −0.13 2154 05 57 38.3 −67 15 37 V 39 9.20 −0.56 0.10 62V 12.13 0.68 0.30 2155 05 58 34.6 −65 28 36 VI 45 9.51 −0.45 0.10 62V 12.60 0.80 0.23 2157 05 57 34.9 −69 11 45 III 25 7.60 −0.45 0.10 60V 10.16 0.19 −0.16 2164 05 58 56.8 −68 30 56 II 23 7.70 −0.45 0.10 60V 10.34 0.10 −0.24 2214 06 12 58.4 −68 15 33 II 22 7.60 −0.45 0.10 60V 10.93 0.11 −0.27 a, b SWB classification and s parameter from Bica et al. (1996, hereafter BCDSP96). c, d Logarithmic age and metallicity from Mackey & Gilmore (2003), except for NGC 1651, which is from Sarajedini et al. (2002). e Reddening from Persson83. Except for NGC 1847 from Nelson & Hodge (1983), and NGC 1967, NGC 1983, NGC 2074 from Meurer et al. (1990). f Aperture diameter in arcsec for BV photometry. Suffix V and T indicates photometry sources, respectively van den Bergh (1981, hereafter VDB81) and BCDSP96. g Optical photometry data from VDB81 and BCDSP96. † Adopted mean value across the LMC of E(B − V) = 0.07 taken from Burnstein & Heiles (1984). 2. Sample and observation 2.2.