Modeling the Mg I from the NUV to MIR

I. The solar case

¹ Instituto de Astronomía y Física del Espacio, CONICET–Universidad de Buenos Aires, Argentina
e-mail: mariela@iafe.uba.ar; jperalta@iafe.uba.ar
² Departamento de Ciencia y Tecnología, UNTREF, Argentina
³ Departamento de Física, Universidad de Buenos Aires, Argentina

Received: 4 August 2021
Accepted: 6 October 2021

Abstract

Context. Semi-empirical models of the solar atmosphere are used to study the radiative environment of any planet in our Solar System. There is a need for reliable atomic data for neutral atoms and ions in the atmosphere to obtain improved calculated spectra. Atomic parameters are crucial to computing the correct population of elements through the whole stellar atmosphere. Although there is very good agreement between the observed and calculated spectra for the Sun, there is still a mismatch in several spectral ranges due to the lack of atomic data and the inaccuracies thereof, particularly for neutrals such as Mg I.

Aims. To represent many spectral lines of Mg I from the near-ultraviolet to the mid-infrared correctly, it is necessary to add and update the atomic data involved in the atomic processes that drive their formation.

Methods. The improvements made to the Mg I atomic model are as follows: i) 127 strong lines, including their broadening data, were added. ii) To obtain these new lines, we increased the number of energy levels from 26 to 85. iii) Photoionization cross-section parameters were added and updated. iv) Effective collision strength (ϒ_ij) parameters were updated for the first 25 levels using the existing data from the convergent close-coupling calculations. One of the most significant changes in our model is given by the new ϒ_ij parameters for transitions involving levels between 26 and 54, which were computed with a multiconfiguration Breit–Pauli distorted-wave (DW) method. For transitions involving superlevels, we calculated the ϒ_ij parameters with the usual semi-empirical formulas.

Results. More than 100 transitions were added to our calculations, increasing our capability of reproducing important features observed in the solar spectra. We found a remarkable improvement in matching the solar spectra for wavelengths higher than 30 000 Å when our new DW ϒ_ij data were used in the model.