Synthetic spectrum calculations of Ca II lines in the Gaia RVS wavelength region.

Abstract: The Gaia space telescope is dedicated to monitor the sky, collect data and create the most precise 3D map consisting of more than 1.7 billion objects in the Milky Way. At the same time, the Radial Velocity Spectrometer (RVS) will collect spectra for ~150 million stars in the wavelength range 847 to 874 nm. This wave range is selected because it coincides with G-and K-type star energy-distribution peaks, as well as containing the strong Ca II infrared triplet lines (λ =8498, 8542, 8662 Å). The aim of this thesis is to create a grid of synthetic spectra in RVS wavelength range which later when compared to the real spectra can be used to determine the chemical composition of the star as well as precise atmospheric parameters. Calculations consist of 198 spectra ranging in effective temperature from Teff =4500 K to 7000 K with various steps, surface gravity log g = 2.5 to 4.5 with the step of 0.5and metallicities [M/H] = −0.5, 0.0 and 0.5 relative to the Solar composition. For calculations MARCS atmosphere models [3], a line list extracted from the VALD3 database [6] and the software SME [7] was used. Spectra calculations were conducted in both classical LTE and refined non-LTE modes for the line formation of calcium.