High-precision stellar abundances of the elements: methods and applications

Abstract

Efficient spectrographs at large telescopes have made it possible to obtain high-resolution spectra of stars with high signal-to-noise ratio and advances in model atmosphere analyses have enabled estimates of high-precision differential abundances of the elements from these spectra, i.e. with errors in the range 0.01 -0.03 dex for F, G, and K stars.Methods to determine such high-precision abundances together with precise values of effective temperatures and surface gravities from equivalent widths of spectral lines or by spectrum synthesis techniques are outlined, and effects on abundance determinations from using a 3D non-LTE analysis instead of a classical 1D LTE analysis are considered.The determination of high-precision stellar abundances of the elements have led to the discovery of unexpected phenomena and relations with important bearings on the astrophysics of galaxies, stars, and planets, i.e. i) Existence of discrete stellar populations within each of the main Galactic components (disk, halo, and bulge) providing new constraints on models for the formation of the Milky Way. ii) Differences in the relation between abundances and elemental condensation temperature for the Sun and solar twins suggesting dust-cleansing effects in proto-planetary disks and/or engulfment of planets by stars; iii) Differences in chemical composition between binary star components and between members of open or globular clusters showing that star-and cluster-formation processes are more complicated than previously thought; iv) Tight relations between some abundance ratios and age for solar-like stars providing new constraints on nucleosynthesis and Galactic chemical evolution models as well as the composition of terrestrial exoplanets.We conclude that if stellar abundances with precisions of 0.01 -0.03 dex can be achieved in studies of more distant stars and stars on the giant and supergiant branches, many more interesting future applications, of great relevance to stellar and galaxy evolution, are probable. Hence, in planning abundance surveys, it is important to carefully balance the need for large samples of stars against the spectral resolution and signal-to-noise ratio needed to obtain high-precision abundances. Furthermore, it is an advantage to work differentially on stars with similar atmospheric parameters, because then a simple 1D LTE analysis of stellar spectra may be sufficient. However, when determining high-precision absolute abundances or differential abundance between stars having more widely different parameters, e.g. metal-poor stars compared to the Sun or giants to dwarfs, then 3D non-LTE effects must be taken into account.

High-resolution Spectroscopic Study of Dwarf Stars in the Northern Sky: Lithium, Carbon, and Oxygen Abundances

“…Every new analysis of these chemical elements in stellar atmospheres contributes to the ongoing discussion of their importance in understanding the Galaxy evolution and whether they constitute a star-planet connection (see, e.g., Delgado Mena et al 2010;González Hernández et al 2010;Brugamyer et al 2011;Petigura & Marcy 2011;Schuler et al 2011;Ramírez et al 2012;Spina et al 2016;Luck 2017;Adibekyan et al 2018;Bensby & Lind 2018;Fu et al 2018;Luck 2018a;Nissen & Gustafsson 2018;Guiglion et al 2019;Pavlenko et al 2019).…”

Precision angular diameters for 16 southern stars with VLTI/PIONIER

“…Internal errors on modern techniques for spectroscopic temperature determination are at the level of < 1.5% (e.g. using the Cannon, Ho et al 2016, trained on values from more fundamental techniques, see Nissen & Gustafsson 2018 for a summary), meaning that in order to be useful, diameter calibration at the level of < 1% is required to put these surveys on an absolute scale. Whilst possible to measure T eff spectroscopically, it is not yet possible to calibrate temperature scales at the < 100 K level from spectra alone (particularly when using different analysis techniques, e.g.…”

Differential abundance analysis of Procyon and θ Sculptoris: Comparison with abundance patterns of solar‐like pairs

“…Because of this, we have based our final model parameters on 12 Fe I lines and 13 Fe II lines with equivalent widths ≲20 mÅ (Table ). Our calculations used local thermodynamic equilibrium and 1‐dimensional models as is still common in differential analyses (Nissen & Gustafsson ).…”

“…These range from consequences of terrestrial planet formation to accretion of differentiated interstellar material. We refer to Nissen & Gustafsson (, see Section 4), RAM14, and other cited papers for details.…”