THE REDDENING OF TYPE-AB RR-LYRAE STARS

Sturch's method for deriving, from observed near-minimum light colors, E(B - V) values for RR Lyrae stars with Bailey's types a or b light curves, is modified in order to avoid use of reddening and metallicity-sensitive U - B colors. Available Preston's DELTA-S values are collected, reduced to a uniform system, and averaged for the numerous stars with independent determinations. The DELTA-S, [Fe/H] calibration is examined and blanketing corrections are derived from synthetic colors of models by Kurucz. Sturch's finding that the intrinsic blanketing-corrected near-minimum light B - V color of a variable can be estimated from its period is verified. The inherent accuracy of the method is discussed and found to depend appreciably on cycle-to-cycle color variations. Comparisons are made with other reddening determinations, in particular those by Lub, Jones, the Epsteins, and by Sturch. Lub's [Fe/H] calibration of his DELTA[B - L] metallicity parameter is found to require corrections especially for high metallicity stars. This has a minor effect on reddening determinations, but estimates of DELTA-S from DELTA-[B - L] can be appreciably affected. Values of E(B - V) are derived from Lub's as well as from the Epsteins' data and found to agree closely with those obtained from Sturch's method as modified here. Estimates of E(B - V) from Jones's (k - b)2 method are found to depend on metallicity. The blanketing corrections determined by Sturch from delta(U - B) values are found to make his E(B - V) values less than found here while his estimated intrinsic colors make his E(B - V) values more found here. Fortuitously, these effects nearly cancel each other.