1994A&A...290..443S

We present an improved fitting procedure for the surface-brightness variant of the Baade-Wesselink method and absolute magnitudes and distances to two RR Lyrae stars in M 5 and two in M 92. The new statistical method has been developed to more objectively match the spectroscopic and photometric angular diameter variations, which is necessary to successfully cope with the lower precision in the K band photometry for the faint cluster variables vs. the bright field RR Lyraes previously studied. Within the uncertainties we do not detect a significant difference between the cluster and field RR Lyrae stars. The distances to M 5 and M 92 are estimated to be 14.37±0.18mag and 14.60±0.26mag respectively. Our results suggest that previous age estimates for M 92 and other metal-poor clusters may be too large although the current uncertainties prevents us from firmly establishing this.