A Metallicity Snapshot of the Small Magellanic Cloud from Spectra of RR Lyrae Stars

Abstract: Using spectra of RR Lyrae stars in the Small Magellanic Cloud (SMC) a metallicity snapshot from an early epoch in the history of the SMC could possibly be obtained. The SMC, one of our closest neighbours in the Local Group of galaxies, offers the opportunity to study another galaxy close-up. The history of the SMC can be traced using the chemical characteristics of its different generations of stars. The early history of the SMC is debated, and it would be desirable to determine a metallicity distribution function (MDF) of such old (about 10^10 years) stars as the RR Lyrae variables in the SMC. This work uses low resolution RR Lyrae spectra extracted from images obtained in September 2005 with the IMACS spectrograph and camera (in multislit mode) on the 6.5 m Magellan I telescope in Chile. By measuring the equivalent widths of the Balmer gamma and delta lines from hydrogen and the Ca II K line from calcium and using Andrew Layden's method, the metallicity of the SMC RR Lyrae stars could be determined. Multislit spectroscopy of RR Lyrae stars in the SMC with a 6.5 m telescope proved to be a challenge -- only 4 stars in the images showed spectra of sufficient quality for a metallicity determination to be made. The metalliticities were found to be in the range expected for RR Lyrae stars, but no MDF could be constructed. In the years since 2005, other groups have had more success studying the MDF of RR Lyraes in the SMC via photometric methods, and their work is briefly reviewed here along with some ideas for future studies.