scholarly journals Chemical composition of giant stars in the open cluster IC 4756

2018 ◽  
Vol 615 ◽  
pp. A165 ◽  
Author(s):  
Vilius Bagdonas ◽  
Arnas Drazdauskas ◽  
Gražina Tautvaišienė ◽  
Rodolfo Smiljanic ◽  
Yuriy Chorniy
Keyword(s):  
Chemical Elements ◽  
Open Cluster ◽  
Theoretical Models ◽  
Open Clusters ◽  
Galactic Chemical Evolution ◽  
Element Abundances ◽  
Giant Stars ◽  
Thin Disc ◽  
The Mean ◽  
Red Giant

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 ± 0.05 dex. 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 (~ 800 Myr), 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.

scholarly journals OCCASO – III. Iron peak and α elements of 18 open clusters. Comparison with chemical evolution models and field stars

2019 ◽  
Vol 490 (2) ◽  
pp. 1821-1842 ◽  
Author(s):  
L Casamiquela ◽  
S Blanco-Cuaresma ◽  
R Carrera ◽  
L Balaguer-Núñez ◽  
C Jordi ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Chemical Abundances ◽  
Homogeneous Sample ◽  
Giant Stars ◽  
Stellar Nucleosynthesis ◽  
Solar Abundances ◽  
Red Giant

ABSTRACT The study of open-cluster chemical abundances provides insights on stellar nucleosynthesis processes and on Galactic chemo-dynamical evolution. In this paper we present an extended abundance analysis of 10 species (Fe, Ni, Cr, V, Sc, Si, Ca, Ti, Mg, O) for red giant stars in 18 OCCASO clusters. This represents a homogeneous sample regarding the instrument features, method, line list and solar abundances from confirmed member stars. We perform an extensive comparison with previous results in the literature, and in particular with the Gaia FGK Benchmark stars Arcturus and $\mu$-Leo. We investigate the dependence of [X/Fe] with metallicity, Galactocentric radius (6.5 kpc < RGC < 11 kpc), age (0.3 Gyr < Age < 10 Gyr), and height above the plane (|z| < 1000 pc). We discuss the observational results in the chemo-dynamical framework, and the radial migration impact when comparing with chemical evolution models. We also use APOGEE DR14 data to investigate the differences between the abundance trends in RGC and |z| obtained for clusters and for field stars.

scholarly journals Asteroseismology of Red-Giant Stars as a Novel Approach in the Search for Gravitational Waves

2015 ◽  
Vol 11 (A29B) ◽  
pp. 363-364
Author(s):  
Tiago L. Campante ◽  
Ilídio Lopes ◽  
D. Bossini ◽  
A. Miglio ◽  
W. J. Chaplin
Keyword(s):  
Gravitational Waves ◽  
Open Clusters ◽  
Red Giants ◽  
Natural Oscillations ◽  
Giant Stars ◽  
Novel Approach ◽  
Oscillation Modes ◽  
The Mean ◽  
Red Giant Stars ◽  
Red Giant

AbstractStars are massive resonators that may be used as gravitational-wave (GW) detectors with isotropic sensitivity. New insights on stellar physics are being made possible by asteroseismology, the study of stars by the observation of their natural oscillations. The continuous monitoring of oscillation modes in stars of different masses and sizes (e.g., as carried out by NASA's Kepler mission) opens the possibility of surveying the local Universe for GW radiation. Red-giant stars are of particular interest in this regard. Since the mean separation between red giants in open clusters is small (a few light years), this can in principle be used to look for the same GW imprint on the oscillation modes of different stars as a GW propagates across the cluster. Furthermore, the frequency range probed by oscillations in red giants complements the capabilities of the planned eLISA space interferometer. We propose asteroseismology of red giants as a novel approach in the search for gravitational waves.

scholarly journals Open cluster remnants in low-density Galactic fields

2009 ◽  
Vol 5 (S266) ◽  
pp. 487-490
Author(s):  
D. B. Pavani ◽  
L. O. Kerber ◽  
E. Bica ◽  
W. J. Maciel
Keyword(s):  
Galactic Disk ◽  
Information Source ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Theoretical Models ◽  
Open Clusters ◽  
Low Density ◽  
Statistical Tool ◽  
General Picture ◽  
Disk Evolution

AbstractOpen cluster remnants (OCRs) are fundamental objects to investigate open cluster dissolution processes (e.g., Bica et al. 2001; Carraro 2002; Pavani et al. 2003; Carraro et al. 2007; Pavani & Bica 2007). They are defined as poorly populated concentrations of stars, with enough members to show evolutionary sequences in colour–magnitude diagrams (CMDs) as a result of the dynamical evolution of an initially more massive physical system. An OCR is intrinsically poorly populated, which makes its differentiation from field-star fluctuations difficult. Among the possible approaches to establish the nature of OCRs, we adopted CMD analysis combined with a robust statistical tool applied to 2mass data. In addition, photometry is the main information source available for possible OCRs (POCRs). We developed a statistical diagnostic tool to analyse the CMDs of POCRs and verify them as physical systems, explore membership probabilityies taking into account field contamination and derive age, distance and reddening values in a self-consistent way. We present the results of our analysis of 88 POCRs that are part of a larger sample that is widely distributed across the sky, with a significant density contrast of bright stars compared to the Galactic field. The 88 objects are projected onto low-density Galactic fields, at relatively high latitudes (|b| > 15°). Studies of larger POCR samples will provide a better understanding of OCR properties and constraints for theoretical models, including new insights into the evolution of open clusters and their dissolution rates. The results of this ongoing survey will provide a general picture of these fossil stellar systems and their connection to Galactic-disk evolution.

scholarly journals Formation history of open clusters constrained by detailed asteroseismology of red giant stars observed byKepler

2017 ◽  
Vol 160 ◽  
pp. 05002
Author(s):  
Enrico Corsaro ◽  
Yueh-Ning Lee ◽  
Rafael A. García ◽  
Patrick Hennebelle ◽  
Savita Mathur ◽  
...  
Keyword(s):  
Open Clusters ◽  
Giant Stars ◽  
Formation History ◽  
History Of ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals 12C/13C isotopic ratios in red-giant stars of the open cluster NGC 6791

2017 ◽  
Vol 474 (4) ◽  
pp. 4810-4817 ◽  
Author(s):  
László Szigeti ◽  
Szabolcs Mészáros ◽  
Verne V Smith ◽  
Katia Cunha ◽  
Nadège Lagarde ◽  
...  
Keyword(s):  
Open Cluster ◽  
Isotopic Ratios ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals RADIAL VELOCITIES AND METALLICITIES OF RED GIANT STARS IN THE OLD OPEN CLUSTER NGC 7762

2016 ◽  
Vol 152 (6) ◽  
pp. 224 ◽  
Author(s):  
Giovanni Carraro ◽  
Eugene A. Semenko ◽  
Sandro Villanova
Keyword(s):  
Open Cluster ◽  
Radial Velocities ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

The evolution of the Milky Way’s radial metallicity gradient as seen by APOGEE, CoRoT, and Gaia

2018 ◽  
Vol 14 (A30) ◽  
pp. 257-257
Author(s):  
Friedrich Anders ◽  
Ivan Minchev ◽  
Cristina Chiappini
Keyword(s):  
Milky Way ◽  
Past History ◽  
Open Clusters ◽  
Dynamical Models ◽  
Giant Stars ◽  
The Past ◽  
The Status ◽  
History Of ◽  
Abundance Profile ◽  
Red Giant

AbstractThe time evolution of the radial metallicity gradient is one of the most important constraints for Milky Way chemical and chemo-dynamical models. In this talk we reviewed the status of the observational debate and presented a new measurement of the age dependence of the radial abundance gradients, using combined asteroseismic and spectroscopic observations of red giant stars. We compared our results to state-of-the-art chemo-dynamical Milky Way models and recent literature results obtained with open clusters and planetary nebulae, and propose a new method to infer the past history of the Galactic radial abundance profile.

scholarly journals The Gaia-ESO survey: Calibrating a relationship between age and the [C/N] abundance ratio with open clusters

2019 ◽  
Vol 629 ◽  
pp. A62 ◽  
Author(s):  
G. Casali ◽  
L. Magrini ◽  
E. Tognelli ◽  
R. Jackson ◽  
R. D. Jeffries ◽  
...  
Keyword(s):  
Open Cluster ◽  
Empirical Relationship ◽  
Star Clusters ◽  
Open Clusters ◽  
Open Star Clusters ◽  
Mixing Processes ◽  
Dwarf Stars ◽  
Additional Tool ◽  
Giant Stars ◽  
Stellar Ages

Context. In the era of large high-resolution spectroscopic surveys such as Gaia-ESO and APOGEE, high-quality spectra can contribute to our understanding of the Galactic chemical evolution by providing abundances of elements that belong to the different nucleosynthesis channels, and also by providing constraints to one of the most elusive astrophysical quantities: stellar age. Aims. Some abundance ratios, such as [C/N], have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using open star clusters, observed by the Gaia-ESO and APOGEE surveys, as calibrators. Methods. We used stellar parameters and abundances from the Gaia-ESO Survey and APOGEE Survey of the Galactic field and open cluster stars. Ages of star clusters were retrieved from the literature sources and validated using a common set of isochrones. We used the same isochrones to determine for each age and metallicity the surface gravity at which the first dredge-up and red giant branch bump occur. We studied the effect of extra-mixing processes in our sample of giant stars, and we derived the mean [C/N] in evolved stars, including only stars without evidence of extra mixing. By combining the Gaia-ESO and APOGEE samples of open clusters, we derived a linear relationship between [C/N] and (logarithmic) cluster ages. Results. We apply our relationship to selected giant field stars in the Gaia-ESO and APOGEE surveys. We find an age separation between thin- and thick-disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. Conclusions. With this empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. For giant stars, the isochrone fitting method is indeed less sensitive than for dwarf stars at the turn-off. Our method can therefore be considered as an additional tool to give an independent estimate of the age of giant stars. The uncertainties in their ages is similar to those obtained using isochrone fitting for dwarf stars.

scholarly journals Pseudo-photometric distances of 30 open clusters

2018 ◽  
Vol 619 ◽  
pp. A132 ◽  
Author(s):  
A. Chelli ◽  
G. Duvert
Keyword(s):  
Spectral Type ◽  
Large Scale ◽  
Open Cluster ◽  
Estimation Method ◽  
Distance Estimation ◽  
Open Clusters ◽  
Distance Modulus ◽  
Stellar Clusters ◽  
The Mean ◽  
The Difference

Aims. We demonstrate that reliable photometric distances of stellar clusters, and more generally of stars, can be obtained using pseudomagnitudes and rough spectral type without having to correct for visual absorption. Methods. We determine the mean absolute pseudomagnitude of all spectral (sub)types between B and K. Distances are computed from the difference between the star’s observed pseudomagnitude and its spectral type’s absolute pseudomagnitude. We compare the distances of 30 open clusters thus derived against the distances derived from TGAS parallaxes. Results. Our computed distances, up to distance modulus 12, agree within 0.1 mag rms with those obtained from TGAS parallaxes, proving excellent distance estimates. We show additionally that there are actually two markedly different distances in the cluster NGC 2264. Conclusions. We suggest that the pseudomagnitude distance estimation method, which is easy to perform, can be routinely used in all large-scale surveys where statistical distances on a set of stars, such as an open cluster, are required.

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