2018A&A...615A.165B


Query : 2018A&A...615A.165B

2018A&A...615A.165B - Astronomy and Astrophysics, volume 615A, 165-165 (2018/7-1)

Chemical composition of giant stars in the open cluster IC 4756.

BAGDONAS V., DRAZDAUSKAS A., TAUTVAISIENE G., SMILJANIC R. and CHORNIY Y.

Abstract (from CDS):


Context. Homogeneous investigations of red giant stars in open clusters contribute to studies of internal evolutionary mixing processes inside stars, which are reflected in abundances of mixing-sensitive chemical elements like carbon, nitrogen, and sodium, while α- and neutron-capture element abundances are useful in tracing the Galactic chemical evolution.
Aims. The main aim of this study is a comprehensive chemical analysis of red giant stars in the open cluster IC 4756, including determinations of 12C/13C and C/N abundance ratios, and comparisons of the results with theoretical models of stellar and Galactic chemical evolution.
Methods. We used a classical differential model atmosphere method to analyse high-resolution spectra obtained with the FEROS spectrograph on the 2.2 m MPG/ESO Telescope. The carbon, nitrogen, and oxygen abundances, 12C/13C ratios, and neutron-capture element abundances were determined using synthetic spectra, and the main atmospheric parameters and abundances of other chemical elements were determined from equivalent widths of spectral lines.
Results. We have determined abundances of 23 chemical elements for 13 evolved stars and 12C/13C ratios for six stars of IC 4756. The mean metallicity of this cluster, as determined from nine definite member stars, is very close to solar - [Fe/H]=-0.02±0.01. Abundances of carbon, nitrogen, and sodium exhibit alterations caused by extra-mixing: the mean 12C/13C ratio is lowered to 19±1.4, the C/N ratio is lowered to 0.79±0.05, and the mean [Na/Fe] value, corrected for deviations from the local thermodynamical equilibrium encountered, is enhanced by 0.14±0.05dex. We compared our results to those by other authors and theoretical models.
Conclusions. Comparison of the α-element results with the theoretical models shows that they follow the thin disc α-element trends. Being relatively young (∼800Myr), the open cluster IC 4756 displays a moderate enrichment of s-process-dominated chemical elements compared to the Galactic thin disc model and confirms the enrichment of s-process-dominated elements in young open clusters compared to the older ones. The r-process-dominated element europium abundance agrees with the thin disc abundance. From the comparison of our results for mixing-sensitive chemical elements and the theoretical models, we can see that the mean values of 12C/13C, C/N, and [Na/Fe] ratios lie between the model with only the thermohaline extra-mixing included and the model which also includes the rotation-induced mixing. The rotation was most probably smaller in the investigated IC 4756 stars than 30% of the critical rotation velocity when they were on the main sequence.

Abstract Copyright: © ESO 2018

Journal keyword(s): stars: abundances - open clusters and associations: individual: IC 4756 - stars: horizontal-branch - stars: evolution

VizieR on-line data: <Available at CDS (J/A+A/615/A165): table1.dat table2.dat>

Simbad objects: 15

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Number of rows : 15
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 * alf Boo RG* 14 15 39.67207 +19 10 56.6730 2.46 1.18 -0.05 -1.03 -1.68 K1.5IIIFe-0.5 2232 0
2 BD+05 3805 * 18 35 47.4314134440 +05 20 17.105979624 10.39 10.57 9.54     G8 19 0
3 HD 171658 * 18 35 58.4613268896 +05 24 59.985225180 9.72 10.08 8.86     K5 27 0
4 BD+05 3818 * 18 36 33.2283499464 +05 12 42.780591540 9.83 10.28 9.01     K0 21 0
5 BD+05 3829 * 18 37 05.2144598832 +05 17 31.621063920 10.58 10.93 9.83     G5 34 0
6 BD+05 3833 * 18 37 20.7739949622 +05 53 43.109227904 10.08 10.43 9.46     G0 21 0
7 BD+05 3835 * 18 37 30.2982427272 +05 12 15.715653660 10.47 10.85 9.77     G5 28 0
8 BD+05 3840 * 18 37 35.8279260456 +05 15 37.811128716 9.44 9.43 8.06     K2 22 0
9 BD+05 3850 SB* 18 38 05.1613660152 +05 24 33.720370164 10.02 10.29 9.24     K0 28 0
10 BD+05 3858 * 18 38 20.7633328128 +05 26 02.301879660 10.05 10.46 9.46     ~ 30 0
11 IC 4756 OpC 18 38 31.2 +05 29 24           ~ 217 0
12 BD+05 3868 * 18 38 43.7886124608 +05 14 19.935885012 10.05 10.38 9.36     G 30 0
13 BD+05 3873 * 18 38 52.9301191680 +05 20 16.508925924 9.93 10.10 9.05     K0 37 0
14 BD+05 3882 * 18 39 17.8751122128 +05 13 48.737856648 10.09 10.37 9.36     G0 33 0
15 BD+05 3906 * 18 40 18.5164988640 +05 18 51.727114368 10.08 10.35 9.27     G5 16 0

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2022.08.08-03:53:32

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