Cobalt-Hydrogen Atomic and Ionic Collisional Data

Svetlana A Yakovleva,Andrey K Belyaev,Maria Bergemann

doi:10.3390/atoms8030034

Abstract

Rate coefficients for inelastic processes in low-energy Co + H,       Co  +  +   H  −     ,       Co  +  + H    , and       Co   2 +   +   H  −     collisions are estimated using the quantum simplified model. Considerations include 44 triplet and 55 quintet molecular states of CoH, as well as 91 molecular states of CoH     +    . The estimations provide the rate coefficients for the 4862 partial processes (mutual neutralization, ion-pair formation, excitation, and de-excitation) in the neutral CoH system, and for the     8190    partial processes in the ionized CoH     +    system,     13 , 052    processes in total. At     T = 6000    K, the rate coefficients with the largest values around     6 ×  10  − 8      cm  3    s   − 1      correspond to the mutual neutralization processes into the     Co (  e 2  F ) + H    and      Co +   (  g 5  F )  + H    final channels in the neutral and ionized systems, respectively. Among the excitation and de-excitation processes in Co + H and in Co     +    + H collisions, at     T = 6000    K, the largest rate coefficients have values around     7 ×  10  − 9      cm  3    s   − 1      and correspond to the processes      Co (  y 2   S ∘  ) + H  →  Co (  e 2  F ;   v 4   D ∘  ) + H     and       Co +   (  h 3  P )  + H  →   Co +   (  g 3  P ;   g 5  P ;   g 5  F )  + H     , respectively. The calculations single out inelastic processes important for non-local thermodynamic equilibrium (NLTE) modelling of Co I and Co II spectra in stellar atmospheres. The test NLTE calculations are carried out, and it is found that the new collision rates have a strong effect on the line formation and NLTE abundance corrections.

Highlights

Determination of the stellar absolute and relative abundances for different chemical elements is one of the fundamental problems in modern astrophysics, see, e.g., reviews [1,2] and references therein, for example, for understanding the Big Bang, stellar evolution, and microscopic processes in stars
Local Thermodynamic Equilibrium (LTE) modelings of stellar spectra provide not sufficiently accurate results, and non-Local Thermodynamic Equilibrium (NLTE) modelings are used for more accurate treatments [1,2]
Calculations of the rate coefficients for inelastic processes in low-energy Co + H, Co+ + H−, Co + H, and Co2+ + H− collisions are performed by means of the quantum simplified model [28,29]

Summary

Introduction

Determination of the stellar absolute and relative abundances for different chemical elements is one of the fundamental problems in modern astrophysics, see, e.g., reviews [1,2] and references therein, for example, for understanding the Big Bang, stellar evolution, and microscopic processes in stars. The lack of reliable data on H-collisional data, i.e., inelastic processes in collisions of atoms and positive ions of a treated chemical element with hydrogen atoms and negative ions, brings the main uncertainty in NLTE modelings due to the highest abundance of hydrogen in the Universe. The astrophysical origin of Co is still poorly understood, as the models of Galactic chemical evolution fail to explain the abundances of Co relative to Fe in the disk and in the halo (e.g., Andrews et al [23], Côté et al [24]) This mismatch is commonly attributed to the uncertainties of core-collapse and SN I models [20]. We compare our results with our previous predictions and quantify the importance of quantum H-collision data in the NLTE modelling of Co lines

Inelastic Collisions with Hydrogen

Spectral Line Modelling

Conclusions