Using the resolution profile of the HERMES spectrograph to model spectral linesNonkulovski, Kristijan (Avtor) Kos, Janez (Mentor) spectrograph: HERMESresolution profilespectral analysisstars: abundancesstars: fundamental parametersThe main objective of this master thesis is to characterize the resolution profile of the HERMES spectrograph used in the GALAH project. Approximately 100 spectra from different stars were used in the whole analysis that were taken as part of the regular GALAH observations. First, we evaluated the line spread function from which we get the resolution profile in two of the four wavelength bands of the spectrograph, red channel 6481-6739 \AA and infra red channel 7590-7890 \AA. We find that the modeled resolution profile and the measured FWHM are in a very good agreement in both of the wavelength bands. Second, we use three methods for modeling the spectral lines. We start by synthesizing spectra with very high resolution R=300000 and then apply the different methods. With the first one, we fix the resolution of the synthetic spectra using the modeled resolution profile. In the second method, we degrade the synthetic spectra to the lowest common resolution R=22000, and in the third, we assume the nominal resolution of the spectrograph R=28000 for both the observed and the synthetic spectra. The synthetic spectra were generated with the help of the iSpec tool and best fit value was calculated with the \chi^2 goodness of fit test. For both of the methods, we calculate the relative uncertainty of the extracted parameters: effective temperature (T_eff), surface gravity (log g), metallicity [M/H], rotational velocity (vsini) and abundances of sodium, calcium, and silicon. Effective temperature and surface gravity show almost no change in the relative uncertainty between the first two methods, metallicity has a lower relative uncertainty when using the lowest common resolution, and rotational velocity is poorly determined with all of the methods. For all of the abundances, we observe better precision when using the modeled resolution profile. The accuracy of the chemical abundances was also calculated by comparing spectra that have similar element abundances in our star cluster. We found that elements (silicon and metallicity) that are determined by modeling lines that are close to the edges of the wavelength range show are more affected by the changing resolution across the wavelength band. Elements in the central part of the wavelength range have the same accuracy for the first two methods. We also conclude that when assuming the nominal resolution of the spectrograph we get the worst precision and accuracy for all of the parameters.20232023-11-18 08:15:15Magistrsko delo/naloga152306VisID: 139568COBISS_ID: 172412931sl