Colors of c-type RR Lyrae Stars and Interstellar Reddening

Abstract

RR Lyrae stars pulsating in the fundamental mode have long been used to measure interstellar reddening, based on their observed uniformity of B − V color at minimum light after small corrections for metallicity and period are applied. However, little attention has been paid to the first overtone pulsators (RRc or RR1). We present new V − I observations of field RRc stars, supplemented with published data from uncrowded RRc in globular clusters. Preliminary results indicate the RRc colors are correlated with period, but appear to be independent of the stars' metallicity. The scatter around the period-color relation is slightly larger than a comparable relation for RRab. Thus, RRc can be useful indicators of line of sight reddening toward old stellar systems, particularly when multiple stars are available as in Oosterhoff II globular clusters and metal-poor galaxies.

Standard Galactic field RR Lyrae II: a Gaia DR2 calibration of the period–Wesenheit–metallicity relation

“…To check the accuracy of these reddenings for individual stars, we determined the (V − I) color at minimum light, which is an established reddening indicator for RRab stars (Sturch 1966;Mateo et al 1995;Guldenschuh et al 2005), and potentially for RRc stars (Layden et al 2013). Since we do not have simultaneous photometry in the V and I bands to compute the minimum light color, we elected to use our smoothed light curves (see Paper I for details on the how the smoothed light curves were obtained) to compute a color curve for each star and applied the extinction correction.…”

“…As shown in Figure 1, our average value of (V − I) 0,min = 0.55 ± 0.03 mag for the RRab stars is in agreement with the canonical value (0.58±0.02, Guldenschuh et al 2005), and since we detect no obvious trends with [Fe/H] or Galactic latitude, we determine that the Feast et al (2008) reddening values are appropriate. For the RRc stars, (V − I) 0,min is defined in the phase interval of 0.45 − 821 4.151 3.221 3.128 2.607 2.455 1.866 1.860 0.893 0.552 0.363 0.208 0 0.65 (Layden et al 2013). In both (V − I) 0,min versus period and Galactic latitude, only RZ Cep is an outlier, with an extremely underestimated extinction.…”

Metal-rich RRc Stars in the Carnegie RR Lyrae Survey

“…Mean absolute magnitudes are M V = +0.6 ± 0.1 (K13) and cyclical variations are M amp 0.25 (Table 1). Similarly, (B − V ) amp ∼ 0.2 (e.g., Figure 3 of Layden et al 2013). The small variations in these photometric quantities combined with the very small observed pulsational phase range centered at φ = 0.33 allowed K13 to adopt a single set of atmospheric parameters except overall metallicity, based on their analysis of higher S/N du Pont echelle spectra of the RRc star YZ Cap (not included in the K13 sample).…”