Accurate abundance analysis of late-type stars: advances in atomic physics

Abstract

The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics. Progress in the understanding, calculation and measurement of atomic properties and processes relevant to the high-accuracy analysis of F-, G-, and K-type stellar spectra is reviewed, with particular emphasis on abundance analysis. This includes fundamental atomic data such as energy levels, wavelengths, and transition probabilities, as well as processes of photoionisation, collisional broadening and inelastic collisions. A recurring theme throughout the review is the interplay between theoretical atomic physics, laboratory measurements, and astrophysical modelling, all of which contribute to our understanding of atoms and atomic processes, as well as to modelling stellar spectra.

Mutual Neutralization in Li+−D− Collisions: A Combined Experimental and Theoretical Study

“…The position of the avoided crossings and the nonadiabatic couplings are employed to compute theoretical partial and total cross sections by means of the multichannel Landau-Zener approach. This method is known to be particularly well suited for processes such as the mutual neutralization reaction in which the attractive PEC of the entrance channel crosses a series of PECs corresponding to the neutral fragments, with results in good agreement with fully quantum-mechanical calculations (Yakovleva et al 2016;Hedberg et al 2014;Barklem 2017;Belyaev et al 2012;Belyaev 2013;Belyaev et al 2014b;Barklem 2016b;Mitrushchenkov et al 2017;Belyaev et al 2014a).…”

“…The accurate determination of stellar abundances, in particular, provides insights into stellar and galactic evolution, as well as Big Bang nucleosynthesis. In order to derive these abundances, the use of non-Local Thermodynamical Equilibrium (non-LTE) models is required as departure from LTE is extremely common in these environments (Asplund 2005;Barklem 2016a). A typical issue in non-LTE models arises from uncertainties in reactive or inelastic collisional rate coefficients (or cross sections) involving hydrogen atoms.…”

“…Recently, significant progress has been accomplished in the theoretical description of mutual neutralization both with rigorous quantum calculations (Croft et al 1999a;Guitou et al 2012;Hedberg et al 2014;Larson et al 2016;Mitrushchenkov et al 2017) or using various asymptotic models (Yakovleva et al 2016;Barklem 2017Barklem , 2016bBelyaev et al 2014a;de Ruette et al 2018), in various collision energy ranges. This includes the theoretical study of mutual neutralization between H − and several elements such as H + (Stenrup et al 2009;Nkambule et al 2016), He + , Li + (Croft et al 1999b,a;Belyaev & Voronov 2018), Be + (Yakovleva et al 2016;Hedberg et al 2014), O + (Barklem 2017), Na + (Dickinson et al 1999), Mg + Guitou et al 2012), Al + (Belyaev 2013), Si + (Belyaev et al 2014b), Ca + (Barklem 2016b;Mitrushchenkov et al 2017) or Cs + (Belyaev et al 2014a).…”

The 3D non-LTE solar nitrogen abundance from atomic lines

“…This level has a different core (2p 2 1 D) than the other high-excitation levels in the figure (2p 2 3 P). As a result, it is only weakly coupled to the rest of the N i system: the electron collisions involving this level are typically an order of magnitude less efficient than collisions involving other levels of comparable energy; while the hydrogen collisions are neglected from the non-LTE model, due to Eqs 8 and 9 of Barklem (2016a).…”

Inelastic processes in collisions of lithium positive ions with hydrogen anions and atoms

“…Among other processes, the experiments treat neutralization processes in collisions between cations and anions. Lithium-hydrogen collisions are of interest, in particular, due to their importance for non-local thermodynamic equilibrium (non-LTE) modelings of cool stellar atmospheres (see, e.g., reviews [8][9][10], and references therein). It has been shown theoretically in reference [11] that the mutual neutralization processes Li + + H − → Li(nl) + H(1s), as well as their inverse processes, the ion-pair production, are important for non-LTE modelings of lithium spectra in cool stellar atmospheres, which are in turn important for determining absolute and relative abundances of lithium.…”