An Oosterhoff Analysis of the Galactic Bulge Field RR Lyrae stars: Implications On Their Absolute Magnitudes

摘要

The period-V-amplitude plane for fundamental mode pulsator RR Lyrae stars in the MACHO Bulge fields is examined. Only stars with "normal" light curves are used in the analysis. Although the RR Lyraes in Bulge globular clusters divide into two distinct groups based on the average periods [12], no gap between Oosterhoff I and II stars in the Bulge field star sample is seen. The main AlogP distribution of the Bulge RRO Lyrae field star population is shifted by about 0.02 days with regard to the Milky Way Oosterhoff I population. Stars with AlogP > 0.06 days are seen in the sample, a rare property of RR Lyrae in Milky Way globular clusters. A comparative study of the Bulge field stars with similar metallicities but different Oosterhoff types is carried out, and it is shown that Bulge field RRO Lyrae variables with OoII-like AlogP values are about 0.2 mag brighter than RRO Lyrae variables with OoI-like AlogP value. Hence, an RR Lyrae M_V~(RR) -[Fe/H] relation may be inaccurate when considering populations with different ΔlogP.