Stellar atmosphere modeling and chemical abundance determinations require the knowledge of spectral line shapes. A spectral line is not infinitely sharp but has a finite width and shape, due to various line broadening mechanisms. This phenomenon is known as broadening of spectral lines. Stark broadening of spectral lines results from the perturbation of atomic/ionic energy levels involved in the electronic transition by interaction with charged particles. Spectral lines of chromium (Cr) in various ionization stages have often been observed in stellar spectra but the theoretical data on Stark broadening for them is scarce.
This work focuses on Stark broadening of Cr lines in the ultraviolet (UV) regionof stellar spectra. The work was divided in two parts: (1) calculation of Stark broadeningdata and (2) the study of its influence on spectral line shapes. We have calculated Stark broadening data using the Modified Semi-Empirical approach (MSE) for 4s-4p transition spectral lines in doubly and triply ionized Cr.
We have used ATLAS9 model atmospheres and the line-formation code SURFACE for calculating synthetic spectra of Cr for several stars under consideration. We compared the theoretical Cr spectral lines based on approximate Stark broadening data with those based on MSE broadening tables. The OB-type main-sequence stars Iota Hercules and Upsilon Orionis, and the subdwarf B-stars CD-24 731, HD199112, and Feige 66 were investigated.