14th World Congress on Computational Mechanics (WCCM) ECCOMAS Congress 2020 Virtual Congress: 11-–15 January 2021 F. Chinesta, R. Abgrall, O. Allix and M. Kaliske (Eds) DESIGN OF AN ARTIFICIAL NEURAL NETWORK FOR THE ANALYSIS OF STELLAR SPECTRA JAIME KLAPP 1 , CELIA R. FIERRO-SANTILLAN 1 , LEONARDO DI G SIGALOTTI 2 AND ISIDORO GITLER 3 1 Departamento de F´ ısica, Instituto Nacional de Investigaciones Nucleares (ININ) Carretera M´ exico-Toluca km. 36.5, La Marquesa, 52750 Ocoyoacac, Estado de M´ exico, Mexico jaime.klapp@inin.gob.mx, celia.fierro.estrellas@gmail.com 2 ´ Area de F´ ısica de Procesos Irreversibles, Departamento de Ciencias B´ asicas, Universidad Aut´ onoma Metropolitana-Azcapotzalco (UAM-A), Av. San Pablo 180, 02200 M´ exico City, M´ exico leonardo.sigalotti@gmail.com 3 Departamento de Matem´ aticas, Centro de Investigaci´ on y de Estudios Avanzados CINVESTAV-IPN Apartado Postal 14–740 07000 M´ exico City, D.F. igitler@math.cinvestav.edu.mx Key words: Artificial neural network, stellar atmospheres, techniques: spectroscopy Abstract. We have developed an artificial neural network, whose purpose is to automatically find in a database of synthetic stellar spectra the one which best reproduces an observed spectrum. Using the equivalent widths of selected spectral lines, the network fits a set of lines related to the physical parame- ters in the stellar atmosphere (i.e., temperature, gravity and mass loss rate). The main advantage of this approach is its scalability. 1 INTRODUCTION All our information about the physical conditions and the chemical composition of stars comes from the study of their electromagnectic spectrum. In massive stars (20M ⊙ ≤ M ⋆ ≤ 120M ⊙ ), we can identify three components of stellar spectrum: the continuum, the absorption and the emission lines. They can give us information about the structure of the atmosphere, since they come from layers located at different depths in the stellar atmosphere (e.g., see Figure 1). The spectrum emitted by the stellar interior where the atmosphere begins is called the continuum. Due to its strong dependence on temperature and the energy distribution, the continuum can be modeled by Planck’s law of blackbody radiation 1 . The absorption lines come from the base of the atmosphere. This region is in local thermodynamic equi- librium (LTE). The atoms in the atmosphere absorb certain characteristic wavelengths of the continuum 1 A blackbody is an ideal radiator that does not exist in the real world. However, many objects, including stars, behave as a blackbody. Blackbody radiation can be produced in a closed cavity whose walls absorb all radiation incident upon them and coming from inside the cavity. The walls and the radiation in the cavity are in equilibrium. Both are at the same temperature, and the walls emit all the energy they receive. 1