Chemical abundances in seven red giants of NGC 2360 and NGC 2447 ? , ? ?
نویسندگان
چکیده
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 (∼ 2M in NGC 2360 and ∼ 3M 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 − 4M 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 − 3M range. The agreement between our Na abundance determinations in NGC 2360 and our model predictions at 2M is very good. In contrast, the overabundance in one of the three stars in NGC 2447 exceeds that predicted at 3M 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.
منابع مشابه
Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants
We present the results of an observational study of the efficiency of deep mixing in globular cluster red giants as a function of stellar metallicity. We determine [C/Fe] abundances based on low-resolution spectra taken with the Kast spectrograph on the 3m Shane telescope at Lick Observatory. Spectra centered on the 4300Å CH absorption band were taken for 42 bright red giants in 11 Galactic glo...
متن کاملThe chemical abundance of the very metal rich old Open Clusters NGC 6253 and NGC 6791 ⋆
Aims. In the framework of a project aiming at deriving in a homogeneous way the properties (age, distance, reddening and detailed chemical abundances) of a large sample of old open clusters, we present here the metal abundance and the abundance ratios of light (C, N, O, Na, Mg, Al, Si, Ca, Ti) and heavier (Cr, Mn, Ni, Ba, Eu) elements in the galactic open clusters NGC 6253 and NGC 6791. Methods...
متن کاملIron abundances from high - resolution spectroscopy of the open clusters NGC 2506 , NGC 6134 , and IC 4651 ⋆
This is the first of a series of papers devoted to derive the metallicity of old open clusters in order to study the time evolution of the chemical abundance gradient in the Galactic disk. We present detailed iron abundances from high resolution (R ∼ > 40, 000) spectra of several red clump and bright giant stars in the open clusters IC 4651, NGC 2506 and NGC 6134. We observed 4 stars of NGC 250...
متن کاملFluorine Abundance Variations in Red Giants of the Globular Cluster M4 and Early-Cluster Chemical Pollution
We present fluorine abundances in seven red-giant members of the globular cluster M4 (NGC 6121). These abundances were derived from the HF (1–0) R9 line at 2.3357μm in high-resolution infrared spectra obtained with the Phoenix spectrograph on Gemini-South. Many abundances in the target stars have been studied previously, so that their overall abundance distributions are well-mapped. The abundan...
متن کامل