Messier 93 - the NGC 2447 Open Star Cluster

Description:

"Chemical abundances of about fifteen elements from oxygen to europium are measured in seven red giants of the two open clusters NGC 2360 and NGC 2447. The effective temperatures of the giants are determined spectroscopically by taking advantage of their known masses (~2 Mo in NGC 2360 and ~3 Mo in NGC 2447) and bolometric magnitudes. The average iron abundances we obtain for the two clusters are [Fe/H]=0.07 for NGC 2360 and [Fe/H]=0.03 for NGC 2447. Evolutionary stellar model calculations are performed in the mass range 1-4 Mo in order to analyze the surface Na and O abundances predicted after the first dredge-up. The sodium abundance shows a well defined correlation with stellar mass in the 2-3 Mo range.

The agreement between our Na abundance determinations in NGC 2360 and our model predictions at 2 Mo is very good. In contrast, the overabundance in one of the three stars in NGC 2447 exceeds that predicted at 3 Mo by ~0.08 dex, which is significant compared to the observational error bars. The effects of core overshooting, convection prescription, metallicity and nuclear reaction rates on the Na surface predictions of our models are investigated. An oxygen deficiency relative to iron by 0.2 dex is measured in our stars, in disagreement with our model predictions. Assuming that the Sun is 0.1-0.3 dex enriched in oxygen relative to neighbor stars could explain the discrepancy."

"We use Two Micron All-Sky Survey (2MASS) to study open clusters in the solar neighborhood. Dias (2003) compiles a catalogue of optical open clusters from literature. The error and consistency are difficult to estimate due to different observational systems and resources. In order to study the effect of dynamical evolution and galactic location on open clusters, we use radial density profile from 2MASS point source catalogue to reestimate the size of clusters. We also discuss the difference between different methods. We find that the sizes of old open clusters are larger, and the number densities of them are smaller. Old open clusters are distributed higher from the disk. We work out the main sequence luminosity function and main sequence mass function of 17 open clusters. We do not find the relation between age and luminosity function and mass function. We conclude that in the contest of main sequence luminosity function and mass function, 2MASS data is suitable for clusters within 2 kpc from the sun and age less than 3×10 8 yr only. Moreover, we find that an interesting result, the power index of field-star luminosity functions on different locations are very similar, the average value is 0.336±0.01"

History of Observation:

"Nebula, about 1 1/4 deg north preceding the bright star in the Ship [or more exactly] preceding the 1st Navis [Puppis] towards 23 Canis majoris. My Brother examined it with [magnification] 460 and found not less than 20 stars, with 227 above 40. with a compound eyepiece perhaps 100 and 150 very beautiful, nothing nebulous among them. Messier has it not."

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