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Stellar Population Astrophysics (SPA) with the TNG. GIANO-B Astronomy & Astrophysics manuscript no. origlia c ESO 2019 August 22, 2019 Stellar population astrophysics (SPA) with the TNG? GIANO-B spectroscopy of red supergiants in Alicante 7 and Alicante 10 L. Origlia1, E. Dalessandro1, N. Sanna2, A. Mucciarelli3; 1, E. Oliva2, G. Cescutti4, M. Rainer2, A. Bragaglia1, and G. Bono5; 6 1 INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, I-40129, Bologna, Italy e-mail: [email protected] 2 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Firenze, Italy 3 Dipartimento di Fisica e Astronomia, Universitá degli Studi di Bologna, Via Gobetti 93/2 - I-40129, Bologna, Italy 4 INAF - Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34143, Trieste, Italy 5 Dipartimento di Fisica e Astronomia, Universitá degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133, Roma, Italy 6 INAF - Osservatorio Astronomico di Roma, Via Frascati 33, I-00040, Monte Porzio Catone, Italy Received .... ; accepted ... ABSTRACT Aims. The Scutum complex in the inner disk of the Galaxy hosts a number of young clusters and associations of red supergiant stars that are heavily obscured by dust extinction. These stars are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. Methods. Within the SPA Large Programme at the TNG, we secured GIANO-B high-resolution (R'50,000) YJHK spectra of 11 red supergiants toward the Alicante 7 and Alicante 10 associations near the RSGC3 cluster. Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to measure several hundreds of atomic and molecular lines that are suitable for chemical abundance determinations. We also measured a prominent diffuse interstellar band at λ1317.8 nm (vacuum). This provides an independent reddening estimate. Results. The radial velocities, Gaia proper motions, and extinction of seven red supergiants in Alicante 7 and three in Alicante 10 are consistent with them being members of the associations. One star toward Alicante 10 has kinematics and low extinction that are inconsistent with a membership. By means of spectral synthesis and line equivalent width measurements, we obtained chemical abundances for iron-peak, CNO, alpha, other light, and a few neutron-capture elements. We found average slightly subsolar iron abundances and solar-scaled [X/Fe] abundance patterns for most of the elements, consistent with a thin-disk chemistry. We found depletion of [C/Fe], enhancement of [N/Fe], and relatively low 12C=13C <15, which is consistent with CN cycled material and possibly some additional mixing in their atmospheres. Key words. Techniques: spectroscopic – stars: supergiants – stars: abundances – infrared: stars 1. Introduction peak, CNO, alpha, neutron-capture, Li, Na, Al, and other light element abundances with the necessary high accuracy. These dif- Stellar population astrophysics experiences a golden era because ferent elements are synthesized in stars and supernovae with dif- of the Gaia mission and ongoing and near-future massive photo- ferent mass progenitors and are therefore released into the in- metric, astrometric, and spectroscopic surveys that set the obser- terstellar medium with different time delays with respect to the vational framework for an exhaustive description of the struc- onset of the star formation event. ture of the Milky Way (MW) and its satellites. Optical and near-infrared (NIR) high-resolution (HR) spectroscopy is cru- cial to provide the complementary detailed chemical tagging 1.1. SPA Large Programme of selected stellar populations, in order to constrain timescales The unique combination of the High Accuracy Radial velocity arXiv:1908.07779v1 [astro-ph.SR] 21 Aug 2019 and overall formation and chemical enrichment scenarios. Only Planet Searcher for the Northern emisphere (HARPS-N) and echelle spectra with simultaneous HR and wide spectral cover- GIANO-B echelle spectrographs at the Telescopio Nazionale age might be able to allow measurements of the full set of iron- Galileo (TNG), which together cover almost the full optical and ? NIR range out to the K band, is ideal to sample the luminous Based on observations made with the Italian Telescopio Nazionale stellar populations of the the MW thin disk over almost its entire Galileo (TNG) operated on the island of La Palma by the Fundación extension, as seen from the Northern Hemisphere at a spectral Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de resolution R≥50,000. Thus, taking advantage of this HR capa- Astrofisica de Canarias. This study is part of the Large Program titled bility, we proposed a Large Program called the SPA - Stellar SPA - Stellar Population Astrophysics: the detailed, age-resolved chem- Population Astrophysics: detailed age-resolved chemistry of the istry of the Milky Way disk (PI: L. Origlia), granted observing time with Milky Way disk (Program ID A37TAC_13, PI: L. Origlia). Ob- HARPS-N and GIANO-B echelle spectrographs at the TNG. serving time has been granted starting from June 2018. The SPA Article number, page 1 of 8 A&A proofs: manuscript no. origlia Large Programme aims at obtaining high-quality spectra of more for RSGC2 and RSGC3, respectively, from tmeasurement of the than 500 stars in the MW thin disk and associated star clusters at Ca II triplet lines. different Galactocentric distances, including the poorly explored Some chemical abundances of Fe, C, O, and other alpha el- inner disk. We will observe luminous giant and supergiant stars ements were derived for stars in RSGC1 and RSGC2 (Davies in young star clusters and associations, luminous Cepheid and et al. 2009b) using NIRSPEC-Keck spectra at a resolution Mira variables across the entire thin disk, and main-sequence R≈17,000. They suggest slightly subsolar abundances. (MS) and other evolved stars of open clusters in the solar neigh- RSGs are very luminous NIR sources even in highly red- borhood. dened environments, such as the inner Galaxy, and they can be The proposed observations will allow us to provide a detailed spectroscopically studied at HR even with 4 m class telescopes mapping of possible gradients, cosmic spreads, and other inho- when these are equipped with efficient echelle spectrographs. A mogeneities of individual abundances and abundance ratios. We few years ago, during the commissioning and science verifica- will also be able to answer a number of open questions regarding tion of GIANO (see, e.g., Oliva et al. 2012a,b, 2013; Origlia et disk formation, evolution, and chemical enrichment, and we will al. 2014), we therefore acquired HR (R≈50,000) YJHK spectra perform critical tests of stellar evolution and nucleosynthesis. of a few RSGs in the RSGC2 and RSGC3 clusters. This will maximize the scientific return and the overall legacy In particular, we observed three RSGs in RSGC2 in July value for astrophysics. 2012 and five RSGs RSGC3 in October 2013. Detailed RVs and Based on this detailed chemical tagging and complementary chemical abundances of iron-peak, CNO, alpha, and a few other kinematic and evolutionary information from the Gaia mission metals have been published in Origlia et al. (2013, 2016). They and other surveys, we expect in particular to set the framework confirmed slightly subsolar iron and iron-peak elements, some for a comprehensive chemodynamical modeling of the disk for- depletion of carbon and enhancement of nitrogen, and approxi- mation and evolution. We hope to be able to distinguish radial mately solar-scale [X/Fe] abundance ratios for the other metals. migration from in situ formation scenarios (e.g., da Silva et al. Prompted by the results of these pilot projects, we decided to 2016, and references therein) and the overall chemical enrich- perform a more systematic investigation of the RSGs in the Scu- ment history. In addition, given the expected high quality of tum complex. As part of the SPA Large Program at the TNG, we the acquired spectra and the target properties, we will be able are observing a representative sample of luminous RSG stars, to perform the following stellar evolution tests and calibrations: candidate members of the young clusters and associations in the i) a first systematic investigation of the dependence of period- Scutum complex, using the refurbished GIANO-B spectrograph. luminosity relations of variable stars on their detailed chemical This first paper presents the derived RVs and chemical abun- content, ii) a probe of the poorly explored physics and nucle- dances for RSG candidate members of the Alicante 7 and Ali- osynthesis of red supergiants (RSGs), and iii) a probe of crucial cante 10 associations near the RSGC3 star cluster. stellar evolution parameters, such as convection, diffusion, mix- ing, rotation, and magnetic fields in MS and evolved stars for 3. Observations and data reduction different stellar ages and evolutionary stages. GIANO (Origlia et al. 2014) is the HR (R'50,000) YJHK (950– 2450 nm) spectrometer of the TNG telescope. GIANO was de- 2. High-resolution spectroscopy in the Scutum signed to receive light directly from a dedicated focus of the complex TNG. The instrument was provisionally commissioned in 2012 and was used in the GIANO-A configuration. In this position, In the central region of the MW close to the base of the Scutum- the spectrometer was positioned on the rotating building and fed Crux arm and the tip of the long bar, at a distance of ≈3.5 kpc through a pair of fibers that were connected to another focal sta- from the Galactic center, lies a giant region of star formation tion (Tozzi et al. 2014). The spectrometer was eventually moved that is known as the Scutum complex. This region is character- to the originally foreseen configuration in 2016. This configura- ized by three young and massive clusters: RSGC1 (Figer et al.
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