3 Conclusions

We have presented accurate V-band CCD photometry of 65 RR Lyr variables in the globular cluster M 5. Among these stars we have detected 49 fundamental mode pulsators, 15 1st overtone pulsators and one possible 2nd overtone pulsator.

Four of our RRc stars with shortest periods show remarkably similar light curves with a clear bump visible just before the maxima and increased scatter of the observational points around maximum light. We suggest that these features, due to the short pulsation periods of the stars, are caused by interaction between the first and the second overtones of radial pulsations.

Our precise photometry allowed us to obtain accurate Fourier coefficients for 14 RRc stars (twice as many as in previous investigations) and to estimate the physical parameters of these objects. We have measured the mean mass of these stars to be 0.54  ${\cal M}_\odot$, the mean logarithm of luminosity $L/L_{\odot}$equal to 1.69, the mean effective temperature of 7353 K and the mean relative helium abundance equal to 0.28. These values are consistent with the previous determinations of physical parameters of M 5 and also with recent theoretical models (Reid 1996; Clement & Shelton 1997; Sandquist et al. 1996; Caputo et al. 1999).

As many as 26 out of the 49 observed RRab stars have regular light curves as measured by the $D_{\rm m}$ parameter of KJ and thus are suitable for estimating the absolute magnitude, metallicity and effective temperature from the Fourier coefficients of these stars. From this sample we obtained M_V=0.81 mag, ${\rm [Fe/H]}=-1.23$ and $T_{\rm eff}=6465$ K. The derived metallicity corresponds to the Jurcsik (1995) scale which was used by KJ for calibrating their method. Jurcsik (1995) gave ${\rm [Fe/H]}=-1.25$ for M 5 on her scale and this value is in excellent agreement with our estimate.

We also found that six of the regular RRab variables are in a more advanced evolutionary state than the rest of our sample. A detailed inspection of the $A_V-\log P$ relations for the RRab stars from M 3 and M 5 suggests that the V amplitude of RRab variables at a given period is a function of the metallicity rather than the Oosterhoff type of the cluster.

We estimate distance moduli of (m -M)_V = 14.47 for the RRc stars in our sample, and (m -M)_V = 14.27 for the RRab stars. A possible correlation between measured luminosity as derived from the Fourier coefficients and apparent brightness was identified for both the RRc and RRab stars in our sample.

Acknowledgements

JK, AO and WK were supported by the Polish Committee of Scientific Research through grant 2P03D-011-12 and by NSF grant AST-9528096 to Bohdan Paczynski. ASC acknowledges support by KBN grant 2P03C-001-12 and WP was supported by KBN grant 2P03-010-15.