Chemical abundances of solar neighbourhood RR Lyrae stars★

Abstract

We have analysed a sample of 18 RR Lyrae stars (17 fundamental-mode -RRaband one first overtone -RRc) and three Population II Cepheids (two BL Her stars and one W Vir star), for which high-resolution (R 30 000), high signal-to-noise (S/N 30) spectra were obtained with either SARG at the Telescopio Nazionale Galileo (La Palma, Spain) or UVES at the ESO Very Large Telescope (Paranal, Chile). Archival data were also analyzed for a few stars, sampling 3 phases for each star. We obtained atmospheric parameters (T eff , logg, v t , and [M/H]) and abundances of several iron-peak and α-elements (Fe, Cr, Ni, Mg, Ca, Si, and Ti) for different pulsational phases, obtaining [α/Fe] =+0.31±0.19 dex over the entire sample covering -2.2<[Fe/H]<-1.1 dex. We find that silicon is indeed extremely sensitive to the phase, as reported by previous authors, and cannot be reliably determined. Apart from this, metallicities and abundance ratios are consistently determined, regardless of the phase, within 0.10-0.15 dex, although caution should be used in the range 0 φ 0.15. Our results agree with literature determinations for both variable and non-variable field stars, obtained with very different methods, including low and high-resolution spectroscopy. W Vir and BL Her stars, at least in the sampled phases, appear indistinguishable from RRab from the spectroscopic analysis point of view. Our large sample, covering all pulsation phases, confirms that chemical abundances can be obtained for RR Lyrae with the classical EW-based technique and static model atmospheres, even rather close to the shock phases.

Evidence for Galactic disc RR Lyrae stars in the solar neighbourhood

“…the literature was carried out to collect information on the elemental abundances of the pericenter peak RR Lyare stars. We found 61 RR Lyrae stars with determined [Ca/Fe] in our sample from the following studies: Chadid et al (2017); Liu et al (2013); Pancino et al (2015); Lambert et al (1996). Calcium is an element resulting from helium burning via α particle capture and is synthesized in massive stars.…”

Metal-rich RRc Stars in the Carnegie RR Lyrae Survey

“…In that work, measured "psuedoequivalent widths" of the K-line and Balmer lines Hβ, Hγ, and Hδ were transformed into metallicities using the high-resolution [Fe/H] abundances of Butler (1975) and Butler et al (1982), and ultimately tied to the globular cluster metallicity scale of Zinn & West (1984). Chadid et al (2017) analyzed 28 newly acquired RRab du Pont echelle spectra and reconsidered the abundance results from earlier high resolutions studies (Clementini et al 1995, Fernley & Barnes 1996, Lambert et al 1996, Nemec et al 2013, Liu et al 2013, Pancino et al 2015and For et al 2011b). These yielded an extensive set of [Fe/H] metallicities and [X/Fe] abundance ratios on an internally consistent system.…”

Local RR Lyrae stars: native and alien

“…This amount of disagreement is not surprising, however, in light of the differences between different high-resolution studies. For example, the 4 stars in common between Fernley & Barnes (1997) and Pancino et al (2015), have a mean deviation of 0.23 dex with σ = 0.42. The differences between high-resolution measurements for RRL have been discussed by Chadid et al (2017), who pointed out that many high-resolution [Fe/H] scales transform well to the L94 scale.…”