Wide-field CCD photometry of the globular cluster M30

We present new V1 photometry for the halo globular cluster M30 (NGC 7099 = C2137-174) and compute luminosity functions (LFs) in both bands for samples of about 15,000 hydrogen-burning stars from near the tip of the red giant branch (RGB) to over 4 mag below the main-sequence (MS) turnoff (TO). We co nfirm previously observed features of the LF that are at odds with canonica l theoretical predictions: an excess of stars on subgiant branch (SGB) appr oximately 0.4 mag above the turnoff and an excess number of RGB stars relat ive to MS stars. Based on subdwarfs with Hipparcos-measured parallaxes, we compute apparent distance moduli of (m - M)(V) = 14.87 +/- 0.12 and 14.65 /- 0.12 for reddenings of E(V - I) = 0.06 and 0.02, respectively. The impli ed luminosity for the horizontal branch (HB) at these distances is M-V(HB) = 0.11 and 0.37 mag. The two helium indicators we have been able to measure (R and Delta) both indicate that M30's helium content is high relative to those in other clusters of similar metallicity. M30 has a larger value for the parameter Delta V-TO(HB) than nay of the other similarly metal-poor clu sters for which this quantity can be reliably measured. This suggests that M30 has either a larger age or higher helium content than all of the other metal-poor clusters examined. The color-difference method for measuring rel ative ages indicates that M30 is coeval with the metal-poor clusters M68 an d M92.