The Clusters AgeS Experiment (CASE): RR Lyrae variables in the globular cluster NGC 6362

Abstract

We present V- and B-band charge-coupled device (CCD) photometry of 35 RR Lyr stars in the Southern hemisphere globular cluster NGC 6362. Fourier decomposition of the light curves was used to estimate the basic properties of these variables. From the analysis of the RRc stars we obtain a mean mass M=0.531±0.014 M⊙, luminosity log L/L⊙=1.656±0.006, effective temperature Teff=7429±20 and helium abundance Y=0.292±0.002. The mean values of the absolute magnitude, metallicity (on Jurcsik's scale) and effective temperature for 14 RRab stars with ‘regular’ light curves are: MV=0.86±0.01,[Fe/H]=−0.93±0.04 and Teff=6555±25, respectively. From the B–V colours, periods and metallicities of the RRab stars we estimate the colour excess for NGC 6362 to be equal to E(B–V)=0.08±0.01. Using this value we derive the colours of the blue and red edges of the instability strip in NGC 6362 to be (B–V)BE0=0.17 and (B–V)RE0=0.43. From the relations between the Fourier coefficients of RRab and RRc stars and their absolute magnitudes we estimate the apparent distance modulus to NGC 6362 to be (m—M)V=14.46±0.10. From the mean value of log L/L⊙ of the RRc stars we obtain 14.59±0.03. The V-band light curves of three of the RRc stars exhibit changes in amplitude of over 0.1 mag on the time-scale of around one week. Near the radial first overtone frequency we find one or two peaks, which strongly suggests that these variables belong to the newly identified group of non-radial pulsating RR Lyr stars.