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Post Info TOPIC: NGC 4337
Blobrana


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Title: Abundance analysis of red clump stars in the old, inner disc, open cluster NGC 4337: a twin of NGC 752?
Author: Giovanni Carraro (ESO-Chile), Lorenzo Monaco (ESO-Chile), Sandro Villanova (Concepcion)

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. 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. 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. We find that NGC 4337 is marginally more metal-rich than the Sun, with [Fe/H]=+0.12±0.05. The abundance ratios of alpha-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. 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 solar masses.

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Blobrana


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Title: NGC 4337: an over-looked old cluster in the inner disc of the Milky Way
Author: Giovanni Carraro (ESO-Chile), Edgard Giorgi (Universidad de La Plata), Edgardo Costa (Universidad de Chile), Ruben A. Vazquez (Universidad de La Plata)

Galactic open clusters do not survive long in the high density regions of the inner Galactic disc. Inside the solar ring only 11 open clusters are known with ages older than one Gyr. We show here, basing on deep, high-quality photometry, that NGC 4337, contrary to earlier findings, is indeed an old open cluster. The cluster is located very close to the conspicuous star cluster Trumpler 20, as well mis-classified in the past, and that has received so much attention in recent years. NGC 4337 shows a significant clump of He-burning stars which was not detected previously. Its beautiful color-magnitude diagram is strikingly similar to the one of the classical old open clusters IC 4651, NGC 752, and NGC 3680, and this suggests similar age and composition. A spectroscopic study is much needed to confirm our findings. This, in turn, would also allow us to better define the inner disc radial abundance gradient and its temporal evolution.To this aim, a list of clump star candidates is provided.

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NGC 4337 (also ESO 131-SC2, Collinder 254 and OCL 878) is a magnitude +8.9 open star cluster located 1,595 light-years away in the constellation Crux. 

The cluster was discovered by British astronomer John Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at the Cape of Good Hope on the 1st April 1834.

Right Ascension 12h 24m 03.2s, Declination -58° 07' 25"



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