New insights on Ba overabundance in open clusters. Evidence for the intermediate neutron-capture process at play?

Recently, an increasing number of studies were devoted to measure the abundances of neutron-capture elements heavier than iron in stars belonging to Galactic Open Clusters (OCs). OCs span a sizeable range in metallicity (−0.6 ≤ [Fe/H] ≤ +0.4), and they show abundances of light elements similar to disc stars of the same age. A different pattern is observed for heavy elements. A large scatter is observed for Ba, with most OCs showing [Ba/Fe] and [Ba/La] overabundant with respect to the Sun. The origin of this overabundance is not clearly understood. With the goal of providing new observational insights, we determined radial velocities, atmospheric parameters and chemical composition of 27 giant stars members of five OCs: Cr 110, Cr 261, NGC 2477, NGC 2506 and NGC 5822. We used high-resolution spectra obtained with the UVES spectrograph at European Southern Observatory Paranal. We perform a detailed spectroscopic analysis of these stars to measure the abundance of up to 22 elements per star. We study the dependence of element abundance on metallicity and age with unprecedented detail, complementing our analysis with data culled from the literature. We confirm the trend of Ba overabundance in OCs, and show its large dispersion for clusters younger than ∼4 Gyr. Finally, the implications of our results for stellar nucleosynthesis are discussed. We show in this work that the Ba enrichment compared to other neutron-capture elements in OCs cannot be explained by the contributions from the slow neutron-capture process and the rapid neutron-capture process. Instead, we argue that this anomalous signature can be explained by assuming an additional contribution by the intermediate neutron-capture process.

[1]  G. Carraro,et al.  Clues on the Galactic evolution of sulphur from star clusters , 2014, 1407.0485.

[2]  A. Srivastava,et al.  CONFINED PARTIAL FILAMENT ERUPTION AND ITS REFORMATION WITHIN A STABLE MAGNETIC FLUX ROPE , 2014 .

[3]  G. Carraro,et al.  Updated properties of the old open cluster Melotte 66: Searching for multiple stellar populations , 2014, 1404.6748.

[4]  G. Carraro,et al.  A super lithium-rich red-clump star in the open cluster Trumpler 5 , 2014, 1403.6461.

[5]  M. Busso,et al.  s-PROCESSING IN AGB STARS REVISITED. I. DOES THE MAIN COMPONENT CONSTRAIN THE NEUTRON SOURCE IN THE 13C POCKET? , 2014, 1403.6256.

[6]  M. Wiescher,et al.  GALACTIC CHEMICAL EVOLUTION AND SOLAR s-PROCESS ABUNDANCES: DEPENDENCE ON THE 13C-POCKET STRUCTURE , 2014, 1403.1764.

[7]  Michael R. Knox,et al.  GLOBAL NON-SPHERICAL OSCILLATIONS IN THREE-DIMENSIONAL 4π SIMULATIONS OF THE H-INGESTION FLASH , 2013, 1310.4584.

[8]  T. Kawano,et al.  Systematic and correlated nuclear uncertainties in the i-process at the neutron shell closure N = 82 , 2013, 1310.4578.

[9]  F. Herwig,et al.  RELICS OF ANCIENT POST-AGB STARS IN A PRIMITIVE METEORITE , 2013, 1310.2679.

[10]  K. Nomoto,et al.  Nucleosynthesis in Stars and the Chemical Enrichment of Galaxies , 2013 .

[11]  P. Woodward,et al.  HYDRODYNAMIC SIMULATIONS OF H ENTRAINMENT AT THE TOP OF He-SHELL FLASH CONVECTION , 2013, 1307.3821.

[12]  G. Carraro,et al.  Barium and yttrium abundance in intermediate-age and old open clusters , 2013, 1305.1909.

[13]  F. Thielemann,et al.  Abundances of neutron-capture elements in stars of the Galactic disk substructures , 2013, 1303.1730.

[14]  D. Lambert,et al.  Comprehensive abundance analysis of red giants in the open clusters NGC 2527, 2682, 2482, 2539, 2335, 2251 and 2266 , 2013, 1303.1104.

[15]  E. Friel,et al.  ZIRCONIUM, BARIUM, LANTHANUM, AND EUROPIUM ABUNDANCES IN OPEN CLUSTERS , 2013, 1303.4283.

[16]  R. Wyse,et al.  ELEMENTAL ABUNDANCES AND THEIR IMPLICATIONS FOR THE CHEMICAL ENRICHMENT OF THE BOÖTES I ULTRAFAINT GALAXY , 2012, 1212.0598.

[17]  B. Carney,et al.  ELEMENTAL ABUNDANCE RATIOS IN STARS OF THE OUTER GALACTIC DISK. IV. A NEW SAMPLE OF OPEN CLUSTERS , 2012, 1206.6931.

[18]  B. Leibundgut,et al.  Silver and palladium help unveil the nature of a second r-process , 2012, 1205.4744.

[19]  Timothy Heckman,et al.  AN ARCHIVAL Chandra AND XMM-Newton SURVEY OF TYPE 2 QUASARS , 2012, 1205.0033.

[20]  R. Gratton,et al.  The chemical composition of nearby young associations: S-process element abundances in AB Doradus, Carina-Near and Ursa Major , 2012, 1204.2635.

[21]  R. Gratton,et al.  C, N, O abundances and carbon isotope ratios in evolved stars of the open clusters Collinder 261 and NGC 6253 ⋆ , 2012, 1203.6514.

[22]  Sergio Ortolani,et al.  The Gaia-ESO Public Spectroscopic Survey , 2012 .

[23]  R. Hirschi,et al.  Non-standard s process in low metallicity massive rotating stars , 2011, 1112.5548.

[24]  S. Randich,et al.  NEWS ON THE s PROCESS FROM YOUNG OPEN CLUSTERS , 2011, 1112.5290.

[25]  Maria Lugaro,et al.  THE s-PROCESS IN ASYMPTOTIC GIANT BRANCH STARS OF LOW METALLICITY AND THE COMPOSITION OF CARBON-ENHANCED METAL-POOR STARS , 2011, 1112.2757.

[26]  D. Lambert,et al.  Comprehensive abundance analysis of red giants in the open clusters NGC 752, NGC 1817, NGC 2360 and NGC , 2011, 1109.2678.

[27]  J. Lattanzio,et al.  THREE-DIMENSIONAL HYDRODYNAMICAL SIMULATIONS OF A PROTON INGESTION EPISODE IN A LOW-METALLICITY ASYMPTOTIC GIANT BRANCH STAR , 2011, 1109.1289.

[28]  G. Carraro,et al.  A UBVI AND uvbyCaHβ ANALYSIS OF THE INTERMEDIATE-AGE OPEN CLUSTER, NGC 5822 , 2011, 1108.0587.

[29]  Italy,et al.  Chemical abundance analysis of the open clusters Berkeley 32, NGC 752, Hyades, and Praesepe , 2011, 1107.2242.

[30]  E. Muller,et al.  Multidimensional hydrodynamic simulations of the hydrogen injection flash , 2011, 1106.3260.

[31]  S. Randich,et al.  s-PROCESSING IN THE GALACTIC DISK. I. SUPER-SOLAR ABUNDANCES OF Y, Zr, La, AND Ce IN YOUNG OPEN CLUSTERS , 2011, 1105.2208.

[32]  C. Soubiran,et al.  The non-local thermodynamic equilibrium barium abundance in dwarf stars in the metallicity range of −1 < [Fe/H] < +0.3 , 2011, 1104.0534.

[33]  K. Kratz,et al.  What are the astrophysical sites for the r-process and the production of heavy elements? , 2011 .

[34]  W. Aoki,et al.  The s process: Nuclear physics, stellar models, and observations , 2010, 1012.5218.

[35]  F. Montes,et al.  PRODUCTION OF LIGHT-ELEMENT PRIMARY PROCESS NUCLEI IN NEUTRINO-DRIVEN WINDS , 2010, 1007.1275.

[36]  Chris L. Fryer,et al.  CONVECTIVE–REACTIVE PROTON–12C COMBUSTION IN SAKURAI'S OBJECT (V4334 SAGITTARII) AND IMPLICATIONS FOR THE EVOLUTION AND YIELDS FROM THE FIRST GENERATIONS OF STARS , 2010, 1002.2241.

[37]  E. Friel,et al.  ABUNDANCES OF RED GIANTS IN OLD OPEN CLUSTERS. V. Be 31, Be 32, Be 39, M 67, NGC 188, AND NGC 1193 , 2010 .

[38]  D. O. Astronomy,et al.  Abundances and physical parameters for stars in the open clusters NGC 5822 and IC 4756 , 2010, 1002.2547.

[39]  C. Badenes,et al.  METALLICITY AS A SOURCE OF DISPERSION IN THE SNIa BOLOMETRIC LIGHT CURVE LUMINOSITY–WIDTH RELATIONSHIP , 2010, 1002.0681.

[40]  E. Rossetti,et al.  Chemical abundance analysis of the open clusters Cr 110, NGC 2099 (M 37), NGC 2420, NGC 7789, and M 67 (NGC 2682) , 2009, 0910.0723.

[41]  Astronomy,et al.  A holistic approach to carbon-enhanced metal-poor stars , 2009, 0901.4737.

[42]  M. Asplund,et al.  The chemical composition of the Sun , 2009, 0909.0948.

[43]  Italy.,et al.  ENHANCED PRODUCTION OF BARIUM IN LOW-MASS STARS: EVIDENCE FROM OPEN CLUSTERS , 2009, 0901.2743.

[44]  N. Santos,et al.  Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars Stellar metallicity, stellar mass, and giant planets , 2008, 0811.2392.

[45]  N. Mowlavi,et al.  CNONa and 12 C/ 13 C in giant stars of 10 open clusters ⋆ , 2008, 0810.1701.

[46]  K. Kratz,et al.  NUCLEOSYNTHESIS MODES IN THE HIGH-ENTROPY WIND OF TYPE II SUPERNOVAE: COMPARISON OF CALCULATIONS WITH HALO-STAR OBSERVATIONS , 2008, 0901.2541.

[47]  Torino,et al.  The s-Process in Massive Stars at Low Metallicity: The Effect of Primary 14N from Fast Rotating Stars , 2008, 0810.0182.

[48]  D. O. Astronomy,et al.  Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20 , 2008, 0807.2313.

[49]  G. Wasserburg,et al.  Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy , 2008, 0807.0809.

[50]  S. Udry,et al.  Red giants in open clusters - XIV. Mean radial velocities for 1309 stars and 166 open clusters , 2008 .

[51]  S. Villanova,et al.  Old open clusters as key tracers of Galactic chemical evolution II. Iron and elemental abundances in NGC 2324, NGC 2477, NGC 2660, NGC 3960, and Berkeley 32 , 2008 .

[52]  T. Beers,et al.  Nucleosynthesis in the Early Galaxy , 2007, 0709.0417.

[53]  USA,et al.  The Infrared Ca II Triplet as Metallicity Indicator , 2007, 0705.3335.

[54]  M. Asplund,et al.  Chemical Homogeneity in Collinder 261 and Implications for Chemical Tagging , 2006, astro-ph/0611832.

[55]  O. Bienaymé,et al.  High-precision effective temperatures of 215 FGK giants from line-depth ratios , 2006 .

[56]  F. Thielemann,et al.  Neutrino-induced nucleosynthesis of A>64 nuclei: the nu p process. , 2005, Physical review letters.

[57]  M. Reinecke,et al.  Metallicity effect in multi-dimensional SNIa nucleosynthesis , 2005, astro-ph/0507510.

[58]  R. Gratton,et al.  High-resolution spectroscopy of the old open cluster Collinder 261: abundances of iron and other elements , 2005, astro-ph/0505606.

[59]  R. Schiavon,et al.  A library of high resolution synthetic stellar spectra from 300 nm to 1.8 μm with solar and α-enhanced composition , 2005, astro-ph/0505511.

[60]  Potsdam,et al.  alpha-, r-, and s-process element trends in the Galactic thin and thick disks , 2004, astro-ph/0412132.

[61]  R. Gratton,et al.  Iron abundances from high-resolution spectroscopy of the open clusters NGC 2506, NGC 6134, and IC 4651 , 2004, astro-ph/0404298.

[62]  C. Soubiran,et al.  On the correlation of elemental abundances with kinematics among galactic disk stars , 2004, astro-ph/0401234.

[63]  C. Sneden,et al.  # 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A. GALACTIC EVOLUTION OF Sr, Y, AND Zr: A MULTIPLICITY OF NUCLEOSYNTHETIC PROCESSES , 2003 .

[64]  R. Kurucz,et al.  New Grids of ATLAS9 Model Atmospheres , 2004, astro-ph/0405087.

[65]  E. Friel,et al.  Abundances of Red Giants in the Old Open Cluster Collinder 261 , 2003 .

[66]  F. Timmes,et al.  TO APPEAR IN THE ASTROPHYSICAL JOURNAL LETTERS Preprint typeset using LATEX style emulateapj v. 3/3/03 ON VARIATIONS IN THE PEAK LUMINOSITY OF TYPE IA SUPERNOVAE , 2003 .

[67]  A. Bragaglia,et al.  Intermediate-age open clusters: Collinder 110 , 2003, astro-ph/0303662.

[68]  Nathan D. Miller,et al.  Metallicities of Old Open Clusters , 2002 .

[69]  L. Mashonkina.  Non-LTE analysis of the formation of EuII lines in the atmospheres of solar-type stars , 2000 .

[70]  H. C. Stempels,et al.  VALD{2: Progress of the Vienna Atomic Line Data Base ? , 1999 .

[71]  M. Busso,et al.  Neutron Capture in Low-Mass Asymptotic Giant Branch Stars: Cross Sections and Abundance Signatures , 1999, astro-ph/9906266.

[72]  A. Bragaglia,et al.  Old open clusters: UBGVRI photometry of NGC 2506 , 1997, astro-ph/9707076.

[73]  E. Friel,et al.  Deep CCD Photometry of Old Open Clusters , 1997 .

[74]  A. Bragaglia,et al.  CCD PHOTOMETRY OF THE OLD OPEN CLUSTER COLLINDER 261 , 1996, astro-ph/9607081.

[75]  W. Krzemiński,et al.  Discovery of 45 short-period eclipsing binaries in the field of the old open cluster Collinder 261 , 1995 .

[76]  S. Woosley,et al.  Production of the Light p-Process Nuclei in Neutrino-driven Winds , 1994 .

[77]  K. Janes,et al.  The Galactic System of Old Star Clusters: The Development of the Galactic Disk , 1994 .

[78]  富野 康日己,et al.  Annual review 腎臓 , 1987 .

[79]  Ingemar Furenlid,et al.  Solar flux atlas from 296 to 1300 nm , 1985 .

[80]  A. Cameron.  The heavy element yields of neutron capture nucleosynthesis , 1982 .

[81]  R. Rutten,et al.  Empirical NLTE analyses of solar spectral lines , 1978 .

[82]  J. Cowan,et al.  Production of C-14 and neutrons in red giants , 1977 .

[83]  R. Mcclure,et al.  A photometric study of the open cluster NGC 2477. , 1972 .