2002MNRAS.336..841D

Time-series of B, V, I CCD photometry and radial velocity measurements from high-resolution spectroscopy (R = 30 000) covering the full pulsation cycle are presented for the field RR Lyrae star CM Leonis. The photometric data span a 6-yr interval from 1994 to 1999, and allow us to firmly establish the pulsation mode and periodicity of the variable. The derived period P = 0.361 699 d (±0.000001) is very close to the value published in the Fourth Edition of the General Catalogue of Variable Stars (P = 0.361 732 d). However, contrary to what was previously found, the amplitude and shape of the light curve qualify CM Leo as a very regular first overtone pulsator with a prominent hump on the rising branch of its multicolour light curves. According to an abundace analysis performed on three spectra taken near minimum light (0.42 < φ < 0.61), CM Leo is a metal-poor star with metal abundance [Fe/H]=-1.93 ±0.20. The photometric and radial velocity curves of CM Leo have been compared with the predictions of suitable pulsational models to infer tight constraints on the stellar mass, effective temperature, and distance modulus of the star. We derive a true distance modulus of CM Leo of µ₀= 13.11±0.02 mag and a corresponding absolute magnitude of M_V= 0.47±0.04. This absolute magnitude, once corrected for evolutionary and metallicity effects, leads to a true distance modulus of the Large Magellanic Cloud of µ₀= 18.43 ±0.06 mag, in better agreement with the long astronomical distance scale.