The intensities of Balmer lines in low resolution integrated light spectra of globular clusters

Abstract

We introduce a study of the depths and widths of Balmer absorption lines in low resolution ( Δ 𝜆 / 𝜆 ∼ 1000) integrated light (IL) spectra of globular clusters (GCs) depending on the following parameters: age, metallicity (Z) and helium mass fraction (Y). The parameters of stellar atmospheres used to calculate synthetic IL spectra of GCs are set by theoretical isochrones of stellar evolution. As the age increases, the luminosities and effective temperatures of the Main sequence turnoff stars decrease. The analysis of low resolution spectra demonstrates that the depths and widths of the Balmer absorption lines H 𝛿 , H 𝛾 and H 𝛽 in IL spectra of GCs decrease accordingly. On the other hand, as the contribution of hot blue horizontal branch (HB) stars in IL spectra becomes more and more significant, the depths and widths of hydrogen lines increase. These changes are non-monotonic. In this paper we explore characteristics of these changes in spectra of GCs with Z=0.002. Our study contributes to the progress of the research on the properties of HB stars, the contribution of their radiation to IL spectra of GCs and the accuracy of determination of ages and Y for GCs in galaxies.