Study of the departures from LTE in the unevolved stars infra-red spectra

Abstract

We present a study of departures from Local Thermodynamic Equilibrium (LTE) in the formation of infra-red lines of Na I, Mg I, Al I, S I, K I and Sr II in unevolved stars of spectral types F,G,K and metallicities around the solar metallicity. The purpose of this investigation is to identify lines of these species that can be safely treated with the LTE approximation in the infra-red spectra of these types of stars. We employ a set of 40 stars observed with the GIANO spectrograph at the 3.5 m Telescopio Nazionale Galileo (TNG) and previously investigated by Caffau et al. We were able to identify many lines that can be treated in LTE for all the above-mentioned species, except for Sr II. The latter species can only be studied using three lines in the J-band, but all three of them display significant departures from LTE. With our small-size, but high-quality sample we can determine robustly the trends of the abundance ratios with metallicity, confirming the trends apparent from a sample that is larger by several orders of magnitude, but of lower quality in terms of resolution and S/N ratio.

References in corpus (22)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Co-formation of the Galactic disc and the stellar halo
• Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere
• Gaia Data Release 2: Catalogue validation
• Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
• Gaia Data Release 1: Catalogue validation
• In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2
• 4MOST: Project overview and information for the First Call for Proposals
• The Milky Way has no in-situ halo other than the heated thick disc. Composition of the stellar halo and age-dating the last significant merger with Gaia DR2 and APOGEE
• On the correlation of elemental abundances with kinematics among galactic disk stars
• Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
• APOGEE: The Apache Point Observatory Galactic Evolution Experiment
• NLTE determination of the aluminium abundance in a homogeneous sample of extremely metal-poor stars
• Chemical Cartography with APOGEE: Multi-element abundance ratios
• Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg] and [K/Mg] in the Milky Way
• The IAG solar flux atlas: Accurate wavelengths and absolute convective blueshift in standard solar spectra
• NLTE strontium abundance in a sample of extremely metal poor stars and the Sr/Ba ratio in the early Galaxy
• Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tuc
• Abundances of Na, Mg, and K in the atmospheres of red giant branch stars of Galactic globular cluster 47 Tucanae
• Systematic investigation of chemical abundances derived using IR spectra obtained with GIANO

Cited by in corpus (7)

• Comparative high-resolution spectroscopy of M dwarfs -- exploring non-LTE effects
• Probing 3D and NLTE models using APOGEE observations of globular cluster stars
• Sulfur abundances in three Galactic clusters: Ruprecht 106, Trumpler 5 and Trumpler 20
• Influence of departures from LTE on determinations of the sulfur abundances in A-K type stars
• Abundance of strontium in the Galactic globular cluster 47 Tuc
• Cepheid Metallicity in the Leavitt Law (C--MetaLL) survey: VIII. High-Resolution IGRINS Spectroscopy of 23 Classical Cepheids: Validating NIR Abundances
• Sulfur abundances in the Galactic bulge and disk