Stellar Population Astrophysics (SPA) with TNG

Abstract

Context. Open clusters are excellent tracers of the chemical evolution of the Galactic disc. The spatial distribution of their elemental abundances, through the analysis of high-quality and high-resolution spectra, provides insight into the chemical evolution and mechanisms of element nucleosynthesis in regions characterised by different conditions (e.g. star formation efficiency and metallicity). Aims. In the framework of the Stellar Population Astrophysics (SPA) project, we present new observations and spectral analysis of four sparsely studied open clusters located in the solar neighbourhood, namely Collinder 350, Gulliver 51, NGC 7044, and Ruprecht 171. Methods. We exploit the HARPS-N spectrograph at the TNG telescope to acquire high-resolution optical spectra for 15 member stars of four clusters. We derive stellar parameters (Teff, log g, [Fe/H] and ξ) using both the equivalent width (EW) analysis and the spectral fitting technique. We compute elemental abundances for light, α-, iron-peak, and n-capture elements using the EW measurement approach. We investigate the origin of the correlation between metallicity and stellar parameters derived with the EW method for the coolest stars of the sample (Teff < 4300 K). The correlation is likely due to the challenging continuum setting and to a general inaccuracy of model atmospheres used to reproduce the conditions of very cool giant stars. Results. We locate the properties of our clusters in the radial distributions of metallicity and abundance ratios, comparing our results with clusters from the Gaia-ESO and APOGEE surveys. We present the [X/Fe]−[Fe/H] and [X/Fe]−RGC trends for elements in common between the two surveys. Finally, we derive the C and Li abundances as a function of the evolutionary phase and compare them with theoretical models. Conclusions. The SPA survey, with its high-resolution spectra, allows us to fully characterise the chemistry of nearby clusters. With a single set of spectra, we provide chemical abundances for a variety of chemical elements, which are comparable to those obtained in two of the largest surveys combined. The metallicities and abundance ratios of our clusters fit very well in the radial distributions defined by the recent literature, reinforcing the importance of star clusters to outline the spatial distribution of abundances in our Galaxy. Moreover, the abundances of C and Li, modified by stellar evolution during the giant phase, agree with evolutionary prescriptions (rotation-induced mixing) for their masses and metallicities.

Stellar Population Astrophysics (SPA) with the TNG: Stock 2, a little-studied open cluster with an eMSTO

“…The metal-licity found in this work is compatible with that expected for its position. Other similar clusters analysed by Alonso-Santiago et al (2017 are also added along to those previously investigated in the SPA project (Frasca et al 2019;D'Orazi et al 2020;Casali et al 2020;Zhang et al 2021, orange circles). Black lines link results for the same cluster provided by different authors.…”

“…The only exception is the brightest giant, star g1, for which Cantat-Gaudin et al (2018) report a membership probability of P=0.8. We targeted initially the giants, to determine the cluster metallicity and detailed abundances, as we did for other clusters in SPA, for which we mainly selected red clump stars, to have a sample as homogeneous as possible (see Casali et al 2020;Zhang et al 2021). These stars, orange circles in Fig.…”

“…To determine the stellar atmospheric parameters of our targets we used the rotfit code (Frasca et al 2006) adapted to the SPA project workframe, as previously done (see e.g. Frasca et al 2019;Casali et al 2020). The code provides us not only with atmospheric parameters such as effective temperature (T eff ), surface gravity (log g) and iron abundance ([Fe/H], as a proxy of the metallicity) but also with an estimate of the spectral type (SpT) and the projected rotational velocity (v sin i).…”

“…From the latter we only took clusters with data derived from two or more stars and closer than 15 kpc. In addition, open clusters from Alonso-Santiago et al (2017 are also added to the sample along with those previously investigated within the SPA project (Frasca et al 2019;D'Orazi et al 2020;Casali et al 2020;Zhang et al 2021). In total, for this comparison we gathered more than a hundred clusters, ten of which are in common among different datasets.…”

“…Radial metallicity gradient from open clusters studied in the framework of the Gaia-ESO(Baratella et al 2020; Magrini et al 2021, red circles) and APOGEE(Donor et al 2020, green circles) surveys. Other similar clusters analysed byAlonso-Santiago et al (2017 are also added along to those previously investigated in the SPA project(Frasca et al 2019;D'Orazi et al 2020;Casali et al 2020; Zhang et al 2021, orange circles). Black lines link results for the same cluster provided by different authors.…”