Investigating the Relationship between Ca II Equivalent Widths and Metallicity Using DESI Spectra
Faculty Mentor Information
Dr. Katie Devine, College of Idaho; and Dr. Andrea Kunder, Saint Martin's University
Presentation Date
7-16-2026
Abstract
This research focuses on measuring the equivalent width of the calcium triplet (Ca II) line at 8498 Å to probe the relationship between the Ca II 8498 Å equivalent widths and the metallicities of RR Lyrae stars. We can use this relationship to measure the metallicity of larger RR Lyrae samples and use the metallicity to improve the distance estimates of RR Lyrae stars. Measuring metallicity directly is difficult because doing so requires high-resolution spectroscopy, which is only useful for measuring RR Lyrae stars close to the Sun. On the other hand, the Ca II lines are detectable in lower-resolution spectra. A relationship between Ca lines and metallicity would provide an easier, indirect measure of metallicity. Kunder et al. (2024) did a similar study with a smaller number (40) of stars. We will utilize the DESI catalog of over 12,000 RR Lyrae stars to strengthen the Ca II-metallicity relationship. We use a Python script to calculate the equivalent widths and plot the equivalent width vs. metallicity to quantify the correlation. The results from this study will help give us more reliable estimates of metallicities to improve studies on the Milky Way’s structure.
Investigating the Relationship between Ca II Equivalent Widths and Metallicity Using DESI Spectra
This research focuses on measuring the equivalent width of the calcium triplet (Ca II) line at 8498 Å to probe the relationship between the Ca II 8498 Å equivalent widths and the metallicities of RR Lyrae stars. We can use this relationship to measure the metallicity of larger RR Lyrae samples and use the metallicity to improve the distance estimates of RR Lyrae stars. Measuring metallicity directly is difficult because doing so requires high-resolution spectroscopy, which is only useful for measuring RR Lyrae stars close to the Sun. On the other hand, the Ca II lines are detectable in lower-resolution spectra. A relationship between Ca lines and metallicity would provide an easier, indirect measure of metallicity. Kunder et al. (2024) did a similar study with a smaller number (40) of stars. We will utilize the DESI catalog of over 12,000 RR Lyrae stars to strengthen the Ca II-metallicity relationship. We use a Python script to calculate the equivalent widths and plot the equivalent width vs. metallicity to quantify the correlation. The results from this study will help give us more reliable estimates of metallicities to improve studies on the Milky Way’s structure.