NGC 2236: a moderately metal-poor open cluster of Hyades-like age located beyond the Perseus spiral arm

Abstract

New CCD photometry in the Washington system C and T1 passbands down to T1∼ 18.5 mag in the field of the northern open cluster NGC 2236 is presented. T1 magnitudes and C−T1 colours for a total of 1162 stars within an area of 13.6 × 13.6 arcmin2 were measured. These CCD data were supplemented with photoelectric CMT1T2 photometry of 13 red giant candidates. The comparison of the cluster (T1, C−T1) colour–magnitude diagram with theoretical isochrones computed for the Washington system yields E(C−T1) = 1.10 ± 0.10 and for log t= 8.80 (t= 600+100−40 Myr) and Z= 0.008. The derived E(C−T1) value implies E(B−V) = 0.55 ± 0.05. NGC 2236 is then located at 2.5 ± 0.5 kpc from the Sun beyond the Perseus spiral arm and at ∼10.8 kpc from the Galactic centre. A cluster angular diameter of 9.4 arcmin, equivalent to 6.8 pc, was estimated from star counts both within and outside the cluster field. We also derived from the stellar density profile a cluster core radius of rc= 1.7 arcmin (1.2 pc) and an annular corona of Δrc= 1.8rc (2.2 pc). Five independent Washington abundance indices yield a mean cluster metallicity of [Fe/H]=−0.3 ± 0.2, which is not only in reasonably good agreement with the one obtained from the isochrone fit, but also compatible with the existence of a radial abundance gradient in the Galactic disc. We examined the properties of a sample of 20 known open clusters aligned along the line‐of‐sight to NGC 2236. Berkeley 27 appears as the farthest and oldest cluster of the studied sample.

Probing the Large Magellanic Cloud's recent chemical enrichment history through its star clusters

“…Note, however, that the theoretically computed bluest stage during the He-burning core phase is redder than the observed RGC in the CMD of IC 2140 (Fig. 8), a behaviour previously detected in other studies of Galactic and Magellanic Cloud clusters (e.g., Clariá et al 2007;). The age error was estimated considering the isochrones that encompassed those features best.…”

On the metallicity of open clusters

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CCD Washington photometry of 10 open clusters or candidates projected close to the Galactic plane

“…Our goal is to determine reddenings, distances, ages, and if possible also metallicities for poorly known OCs (or candidates), preferably for those located toward the Galactic centre direction (see, e.g., Marcionni et al 2014, hereafter M14). The Washington photometric system has been widely applied to young, intermediate-age and old clusters in the Galaxy (e.g., Geisler et al 1992;Clariá et al 2007;Piatti et al 2009) and in the Magellanic Clouds (e.g., Geisler et al 2003). Geisler et al (1991) and Geisler and Sarajedini (1999) have demonstrated the pross offered by this system in the study of Galactic and/or extragalactic star clusters.…”