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.

Stellar Atmospheric Parameters of ∼11,000 RR Lyrae Stars from LAMOST Spectra

“…Consequently, largeaperture telescopes are required to obtain high signal-to-noise ratio (S/N) spectra for short exposures to weaken the pulsation effect, resulting in high-resolution spectra (HRS) for only a small number of RRLs. For example, Crestani et al (2021) and Kovacs & Jurcsik (2023) have, respectively, collected only 162 and 269 samples of RRLs with HRS. Although the metallicity can be estimated from Fourier parameters of the light curves (Jurcsik & Kovacs 1996;Mullen et al 2021) and the ΔS method from the low-resolution spectrum (Preston 1959;Wallerstein et al 2012), there is still a lack of determination of T eff and g log .…”