Volume 586, February 2016
|Number of page(s)||15|
|Published online||04 February 2016|
1 ASI Science Data Center, via del Politecnico snc, 00133 Rome, Italy
2 Dipartimento di Fisica, Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Rome, Italy
3 INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monte Porzio Catone, Rome, Italy
4 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, PO Box 94249, 1090 GE, Amsterdam, The Netherlands
5 The Observatories of the Carnegie Institute of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA
6 INAF–Osservatorio Astronomico di Teramo, via Mentore Maggini s.n.c., 64100 Teramo, Italy
7 INFN Sezione Napoli, Napoli, Italy
8 Max-Planck-Institut für Astronomy, 69117 Heidelberg, Germany
9 GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, Place Jules Janssen, 92190 Meudon, France
10 UPJV, Université de Picardie Jules Verne, 33 rue St. Leu, 80080 Amiens, France
11 Department of Physics and Astronomy, N283 ESC, Brigham Young University, Provo, UT 84601, USA
12 South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
13 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
14 Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str.1, 85741 Garching, Germany
15 University Observatory Munich, Scheinerstr. 1, 81679 Munich, Germany
16 Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
17 INAF–Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
18 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
19 Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
20 Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching bei München, Germany
21 Laboratoire Lagrange, CNRS/UMR 7293, Observatoire de la Côte d’Azur, Bd de l’Observatoire, CS 34229, 06304 Nice, France
Received: 3 September 2015
Accepted: 19 October 2015
We present new accurate abundances for five neutron-capture elements (Y, La, Ce, Nd, Eu) in 73 classical Cepheids located across the Galactic thin disk. Individual abundances are based on high spectral resolution (R ~ 38 000) and high signal-to-noise ratio (S/N ~ 50−300) spectra collected with UVES at ESO VLT for the DIONYSOS project. Taking into account similar Cepheid abundances provided by our group (111 stars) and available in the literature, we end up with a sample of 435 Cepheids covering a broad range in iron abundances (−1.6 < [Fe/H] < 0.6). We found, via homogeneous individual distances and abundance scales, well-defined gradients for the above elements. However, the slope of the light s-process element (Y) is at least a factor of two steeper than the slopes of heavy s- (La, Ce, Nd) and r- (Eu) process elements. The s-to-r abundance ratio ([La/Eu]) of Cepheids shows a well-defined anticorrelation with both Eu and Fe. On the other hand, Galactic field stars attain an almost constant value and display a mild enhancement in La only when they approach solar iron abundance. The [Y/Eu] ratio shows slight evidence of a correlation with Eu and, in particular, with iron abundance for field Galactic stars. We also investigated the s-process index ([hs/ls]) and we found a well-defined anticorrelation, as expected, between [La/Y] and iron abundance. Moreover, we found a strong correlation between [La/Y] and [La/Fe] and, in particular, a clear separation between Galactic and Sagittarius red giants. Finally, the comparison between predictions for low-mass asymptotic giant branch stars and the observed[La/Y] ratio indicate a very good agreement over the entire metallicity range covered by Cepheids. However, the observed spread at fixed iron content is larger than predicted by current models.
Key words: stars: abundances / stars: variables: Cepheids / stars: oscillations / open clusters and associations: general / Galaxy: disk
Based on spectra collected with the UVES spectrograph available at the ESO Very Large Telescope (VLT), Cerro Paranal, Chile (ESO Proposals: 081.D-0928(A), PI: S. Pedicelli; 082.D-0901(A), PI: S. Pedicelli; 089.D-0767(C), PI: K. Genovali).
Tables 2, 3, 4, and 7 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A125
© ESO, 2016
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