About Stark Broadening of Recombination Radio Lines in the Orion A Nebula

Abstract In order to study the Stark broadening of recombination radio lines in Orion A at a wavelength of 13.5 mm, observations of the H93γ, H94γ, H95γ and H65α lines were carried out at the RT22 (FIAN) radio telescope. An excess of the Stark broadening from the theoretical predictions was found for levels with the main quantum number ( n ) in the range of 93–95 with ∆ n = 2, 3. The recombination radio line H82β was also observed together with the H145(12) and H152(14) lines, the latter also showed an excess of the Stark broadening from the theoretical predictions. It is shown that the Stark broadening data of different frequencies can be consistently described in units of velocities by the dependence ~ n 4–4.5 in the range of n values from 70 to 174. For the first time, the density gradient estimates in this HII region were obtained using the Stark broadening. The electron density of the nebula center turned out to be ≈2 times higher than at a distance of 2 $$' $$ –3 $$' $$ from the center.