Toward more accurate RR Lyrae metallicities

Abstract

By using a large sample of fundamental mode RR Lyrae stars with published spectroscopic iron abundances and gravities, we point out the importance of correcting these abundances by using more accurate temporal gravities. For the 197 stars with multiple spectra, overall we find [Fe/H] standard deviations of 0.167 (as published), 0.145 (shifted by data source zero points), and 0.121 (both zero point shifted and corrected for the static gravity). These improvements are significant at the ~2σ level at each correction step, leading to a clearly significant improvement after both corrections are applied. The higher quality of the gravity-corrected metallicities is also strongly supported by the tighter correlation with the metallicities predicted from the period and Fourier phase, φ31. This work highlights the need for using some external estimates of the temporal gravity in the chemical abundance analysis, rather than relying on a full-fetched spectrum fit that leads to large correlated errors in the estimated parameters.