Volume 568, August 2014
|Number of page(s)||7|
|Section||Galactic structure, stellar clusters and populations|
|Published online||22 August 2014|
Abundance analysis of red clump stars in the old, inner disc, open cluster NGC 4337: a twin of NGC 752?⋆
1 ESO, Alonso de Cordova 3107,
19001 Santiago de
e-mail: firstname.lastname@example.org, email@example.com
2 Departamento de Astronomía, Universidad de Concepción, Casilla 169, Concepción, Chile
Accepted: 16 July 2014
Context. Open star clusters older than ~1 Gyr are rare in the inner Galactic disc. Still, they are objects that hold crucial information for probing the chemical evolution of these regions of the Milky Way.
Aims. We aim at increasing the number of old open clusters in the inner disc for which high-resolution metal abundances are available. Here we report on NGC 4337, which was recently discovered to be an old, inner disc open cluster.
Methods. We present the very first high-resolution spectroscopy of seven clump stars that are all cluster members. We performed a detailed abundance analysis for them.
Results. We find that NGC 4337 is marginally more metal-rich than the Sun, with [Fe/H]= + 0.12 ± 0.05. The abundance ratios of α-elements are generally solar. At odds with recent studies on intermediate-age and old open clusters in the Galactic disc, Ba is under-abundant in NGC 4337 compared with the Sun. Our analysis of the iron-peak elements (Cr and Ni) does not reveal anything anomalous. Based on these results, we estimate the cluster age to be 1.6+0.1-0.1 Gyr, and derive a reddening E(B − V) = 0.23 ± 0.05, and an apparent distance modulus (m − M)V = 12.80 ± 0.15. Its distance to the Galactic centre is 7.6 kpc. With this distance and metallicity, NGC 4337 fits the metallicity gradient for the inner Galactic disc fairly well.
Conclusions. The age and metallicity we measured make NGC 4337 a twin of the well-known old open cluster NGC 752. The red clumps of these two clusters bear an amazing resemblance. But the main sequence of NGC 752 is significantly more depleted in stars than that of NGC 4337. This would mean that NGC 752 is in a much more advanced dynamical stage, being on the verge of dissolving into the general Galactic field. Our results make NGC 4337 an extremely interesting object for further studies of stellar evolution in the critical turn-off mass range 1.1–1.4 M⊙.
Key words: techniques: spectroscopic / Hertzsprung-Russell and C-M diagrams / open clusters and associations: general / open clusters and associations: individual: NGC 4337
© ESO, 2014
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