TOWARDS ACCURATE STELLAR PHOTOMETRY: THE ROLE OF C, N, O AND ALPHA-PROCESS ELEMENTS

摘要

Stars provide most of the light we detect in the universe and enrich our knowledge of chemical evolution of galaxies. In order to have the real view we should know to which extent stars reflect the material from which they were formed and to which they expose effects of their internal evolution. Crucial chemical elements in this sense are carbon and nitrogen, an alteration of which in evolved stars is already a recognized fact. Abundances of oxygen and α-process elements also differ in galactic populations of stars to about a factor of three. In this contribution, on the basis of new stellar model atmospheres, we discuss the sensitivity of stellar spectra to C, N, O and α-process element abundances in order to take this effect into account in photometric observations at the Gaia orbiting observatory. The synthetic spectra of these evolved stars show an enhancement of the NH band at 3300-3500 A by about 10% and several weakened CH and C_2 features. Such spectral changes can be observed photometrically and should be taken into account in the photometric classification of giants. Carbon features in stellar atmospheres show a particularly complex behaviour being very dependent on mixing processes in stars, and on the abundance of oxygen which can also be altered by different reasons. NH bands are more independent indicators of mixing processes in stars. Abundances of α-process elements can be evaluated photometrically by using the direct indicators - Ca Ⅱ H and K lines and Mg Ⅰ b triplet.