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Abstract:
We present V-band CCD photometry of 65 RR Lyr variables from the globular
cluster M5. We have estimated the basic physical parameters for 16 RRc stars
and 26 RRab stars using a Fourier decomposition of the light curves
of the variables. The mean values of mass, luminosity, effective temperature
and relative helium abundance for the RRc stars are measured
to be M=0.54 Msun,
log L=1.69 Teff=7353 K and Y=0.28, respectively.
For the RRab variables the derived mean values of absolute magnitude,
metallicity and effective temperature are: MV=0.81, [Fe/H]=-1.23
and Teff=6465 K. We find that the V amplitude of an RRab star
for a given period is a function of metal abundance rather than Oosterhoff
type. We find significant problems with the calibration of both the zero
point and the scale of the luminosities measured with the Fourier technique.
The apparent distance modulus derived from RRc stars is equal to
14.47±0.11 and it is in good agreement with recent determinations.
On the other hand distance modulus obtained from the sample of RRab stars
(calibrated by the Baade-Wesselink observations of field RR Lyr variables)
is significantly smaller and equal to 14.27±0.04
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