The deep luminosity function of the globular cluster M30

This paper is aimed at determining the mass function in the low-metallicity, post-core collapse globular cluster NGC 7099 = M30, and analyzing its radial trend. New deep CCD photometry is presented in two fields centered at r = 2'.9 and 4'.4 from the center, respectively. We confirm that a good representation of the color-magnitude diagrams is obtained by oxygen-enhanced isochrones (as used by Capaccioli, Ortolani, and Piotto). The best fit yields (m - M)_v = 14.65, E(B-V) = 0.05, and an age of 16 Gyr. Luminosity functions down to V≃25 (M_v≃10.3) are constructed and carefully corrected for contamination by field objects and for incompleteness (see Appendix). Comparison with standard theoretical luminosity functions shows that the mass function, modeled with a power law, has an index x≃1, at variance with the x≃0 found by Richer, Fahlman, and VandenBerg for a field centered at r = 3'.4. An even steeper slope is given by the photometry in an outer field of M30 studied with the 4 m CTIO CCD camera (Piotto et al.). All together, our data agree with the trend of x found by Pryor, Smith, and McClure for a multimass King-Michie model (with or without velocity anisotropy), yielding a global slope x_0 ~0.7. Mass segregation is implied, though marginally, given the errors and the small variation of x expected on theoretical grounds in the radial range explored by our observations. M30 is found to deviate strongly from the mass-function slope versus metallicity relation (McClure et al.); its mass function is as fiat as that of intermediate-metallicity clusters