Issue |
A&A
Volume 653, September 2021
|
|
---|---|---|
Article Number | A67 | |
Number of page(s) | 24 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202141069 | |
Published online | 08 September 2021 |
The Gaia-ESO Survey: a new approach to chemically characterising young open clusters★
II. Abundances of the neutron-capture elements Cu, Sr, Y, Zr, Ba, La, and Ce
1
Dipartimento di Fisica e Astronomia Galileo Galilei,
Vicolo Osservatorio 3,
35122
Padova,
Italy
e-mail: martina.baratella.1@phd.unipd.it
2
INAF – Osservatorio Astronomico di Padova,
vicolo dell’Osservatorio 5,
35122
Padova,
Italy
3
Monash Centre for Astrophysics (MoCA), Monash University, School of Physics and Astronomy,
Clayton,
VIC 3800
Melbourne,
Australia
4
Main Astronomical Observatory, National Academy of Sciences of Ukraine,
Akademika Zabolotnoho 27,
Kyiv
03143,
Ukraine
5
INAF – Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
50125
Firenze,
Italy
6
Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH),
Konkoly Thege Miklós út 15-17,
1121
Budapest,
Hungary
7
ELTE Eötvös Loránd University, Institute of Physics,
Budapest
1117,
Pázmány Péter sétány 1/A,
Hungary
8
E. A. Milne Centre for Astrophysics, Department of Physics and Mathematics, University of Hull,
HU6 7RX,
UK
9
Joint Institute for Nuclear Astrophysics - Center for the Evolution of the Elements,
East Lansing,
MI
48824,
USA
10
INAF – Osservatorio di Astrofisica e Scienza dello Spazio,
via P. Gobetti 93/3,
40129
Bologna,
Italy
11
INAF – Osservatorio Astronomico di Roma,
via Frascati 33,
00040
Monte Porzio Catone (RM),
Italy
12
INAF – Osservatorio Astrofisico di Catania,
via S. Sofia 78,
95123
Catania,
Italy
13
Australian Astronomical Optics, Faculty of Science and Engineering, Macquarie University,
Macquarie Park,
NSW
2113,
Australia
14
Macquarie University Research Centre for Astronomy, Astrophysics & Astrophotonics,
Sydney,
NSW
2109,
Australia
15
European Southern Observatory,
Alonso de Cordova 3107,
Vitacura,
Santiago,
Chile
16
Institute of Theoretical Physics and Astronomy, Vilnius University,
Sauletekio av. 3,
10257
Vilnius,
Lithuania
17
Departmento de Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, Camino Bajo del Castillo s/n,
28692 Villanueva de la Cañada,
Madrid,
Spain
18
Institute of Astronomy, University of Cambridge,
Madingley Road,
Cambridge
CB3 0HA,
UK
19
Lund Observatory, Department of Astronomy and Theoretical Physics,
Box 43,
22100
Lund,
Sweden
20
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences,
ul. Bartycka 18,
00-716
Warsaw,
Poland
21
Instituto de Física y Astronomía, Universidad de Valparaiso,
Gran Bretaña
1111,
Valparaíso,
Chile
22
Núcleo Milenio de Formación Planetaria, NPF, Universidad de Valparaíso,
Chile
23
Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales,
Av. Ejército 441,
Santiago,
Chile
24
Departamento de Ciencias Fisicas, Universidad Andres Bello,
Fernandez Concha 700,
Las Condes,
Santiago,
Chile
Received:
13
April
2021
Accepted:
9
July
2021
Context. Young open clusters (ages of less than 200 Myr) have been observed to exhibit several peculiarities in their chemical compositions. These anomalies include a slightly sub-solar iron content, super-solar abundances of some atomic species (e.g. ionised chromium), and atypical enhancements of [Ba/Fe], with values up to ~0.7 dex. Regarding the behaviour of the other s-process elements like yttrium, zirconium, lanthanum, and cerium, there is general disagreement in the literature: some authors claim that they follow the same trend as barium, while others find solar abundances at all ages.
Aims. In this work we expand upon our previous analysis of a sample of five young open clusters (IC 2391, IC 2602, IC 4665, NGC 2516, and NGC 2547) and one star-forming region (NGC 2264), with the aim of determining abundances of different neutron-capture elements, mainly Cu I, Sr I, Sr II, Y II, Zr II, Ba II, La II, and Ce II. For NGC 2264 and NGC 2547 we present the measurements of these elements for the first time.
Methods. We analysed high-resolution, high signal-to-noise spectra of 23 solar-type stars observed within the Gaia-ESO survey. After a careful selection, we derived abundances of isolated and clean lines via spectral synthesis computations and in a strictly differential way with respect to the Sun.
Results. We find that our clusters have solar [Cu/Fe] within the uncertainties, while we confirm that [Ba/Fe] is super-solar, with values ranging from +0.22 to +0.64 dex. Our analysis also points to a mild enhancement of Y, with [Y/Fe] ratios covering values between 0 and +0.3 dex. For the other s-process elements we find that [X/Fe] ratios are solar at all ages.
Conclusions. It is not possible to reconcile the anomalous behaviour of Ba and Y at young ages with standard stellar yields and Galactic chemical evolution model predictions. We explore different possible scenarios related to the behaviour of spectral lines, from the dependence on the different ionisation stages and the sensitivity to the presence of magnetic fields (through the Landé factor) to the first ionisation potential effect. We also investigate the possibility that they may arise from alterations of the structure of the stellar photosphere due to the increased levels of stellar activity that affect the spectral line formation, and consequently the derived abundances. These effects seem to be stronger in stars at ages of less than ~ 100 Myr. However, we are still unable to explain these enhancements, and the Ba puzzle remains unsolved. With the present study we suggest that other elements, for example Sr, Zr, La, and Ce, might be more reliable tracer of the s-process at young ages, and we strongly encourage further critical observations.
Key words: stars: abundances / stars: fundamental parameters / stars: solar-type / open clusters and associations: general
Based on observations collected with the FLAMES instrument at VLT/UT2 telescope (Paranal Observatory, ESO, Chile), for the Gaia- ESO Large Public Spectroscopic Survey (188.B-3002, 193.B-0936).
NuGrid Collaboration, http://nugridstars.org
© ESO 2021
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