Isochrone fitting of Galactic globular clusters - I. NGC 5904

We present new isochrone fits to colour-magnitude diagrams of the Galactic globular cluster NGC 5904 (M5). We utilize 29 photometric bands from the ultraviolet to mid-infrared by the use of the data from the Hubble Space Telescope, Gaia DR2, Wide-field Infrared Survey Explorer, Sloan Digital Sky Survey (SDSS), and other photometric data. In our isochrone fitting we use the PAdova and TRieste Stellar Evolution Code, the MESA Isochrones and Stellar Tracks, the Dartmouth Stellar Evolution Program, and a Bag of Stellar Tracks and Isochrones for both the solar-scaled and enhanced He and α abundances with a metallicity about [Fe/H]=-1.33 adopted from the literature. All tools provide us with estimates of the distance, age, and extinction law to the cluster. The best-fitting distance, true distance modulus, and age are 7.4 ± 0.3 kpc, 14.34 ± 0.09 mag, and 12.15 ± 1.00 Gyr, respectively. The derived distance agrees with the literature, including the Gaia DR2 parallax with its known global zero-point correction. All the data and models, except some UV and SDSS data, agree with the extinction law of Cardelli-Clayton-Mathis with R_V = 3.60 ± 0.05 and A_V = 0.20 ± 0.02 mag. This extinction is twice as high as generally accepted due to a rather high extinction between 625 and 2000 nm. An offset of the model colours instead of the high extinction in this range is a less likely, yet possible explanation of the discovered large deviations of the isochrones from the data.