New Ccd Observations of the Rr Lyrae Variables in the Oosterhoff Type Ii Cluster M9

CCD observations have been used to study sixteen of the previously known variables in the Oosterhoo type II globular cluster M9. The properties of the RR Lyrae variables in M9 are compared with those in the Oosterhoo type I cluster M3. Methods devised by Simon, Jurcsik and Kovv acs have been used to derive physical parameters for the stars from Fourier analysis. The mean metal abundance so derived for M9, Fe/H]= ?1:77, is in good agreement with the metal abundance derived from spectroscopic observations. All methods for calculating the absolute magnitudes of RR Lyrae variables from Fourier coeecients indicate that the RR Lyrae variables in M9 are more luminous than those in M3. However, there are three RR Lyrae stars in M3 that may be as bright as the M9 stars. These three are thought to be in a more advanced evolutionary state than the other M3 RR Lyrae stars. Absolute magnitudes have also been derived for the RR Lyrae stars in M68 and M107. The diierent methods predict that RR Lyrae stars in metal poor clusters are more luminous than those in more metal rich clusters, but there are inconsistencies in the relative luminosities derived by the diierent methods.