Including Mg I IR lines (<7.2 um) in solar and stellar models

JUAN I. PERALTA; MARIELA C. VIEYTES; ALEJANDRA M.P. MENDEZ; D.M. MITNIK

Cambridge

Conferencia; Cambridge Workshops of Cool Stars, Stellar Systems and the Sun; 2021

Center for Astrophysics, Harvard & Smithsonian MIT Kavli Institute

Considering the imminent launch of the James Webb Space Telescope with IR spectroscopy capabilities, our ability of calculating reliable synthetic stellar spectra in this spectral range must be improved. An important species with strong features in the spectra of late-type stars is the neutral Mg. In the present work we have improved our previous Mg I atomic model adding 128 strong transitions (log(gf) > -1), up to 72 000 Å, and updated several atomic parameters. One of the most important changes is our innovative treatment of the Effective Collision Strengths (ECS) parameters, which describe excitation by collision with electrons. We employed the latest convergent close-coupling calculations (CCC) by Barklem et al. (2017) up to level 25. For transitions involving levels between 26 and 54, we compared the influence in the spectrum of two different sets of ECS parameters: the widely used combination of Seaton (1962) (for allowed transitions) plus van Regemorter (1962) (for forbidden transitions) formulas, and new ECS obtained in this work using the multi–conguration Breit–Pauli distorted–wave (DW) method. We found an overall better agreement between observed and synthetic IR spectral lines when the combination CCC and the new DW calculations for the ECS were used. This result opens the possibility of a new and more reliable approach than the formulas of Seaton and van Regemorter as methods of calculating ECS for Mg I and other species in the stellar atmospheres, when the CCC method is not available.