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 utilise 29 photometric bands from the
ultraviolet to mid-infrared by use of the data from the {\it Hubble Space
Telescope}, {\it Gaia} DR2, {\it 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 both for the solar-scaled and enhanced He and $\alpha$
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-fit distance, true distance modulus, and age are
$7.4\pm0.3$ kpc, $14.34\pm0.09$ mag, and $12.15\pm1.00$ Gyr, respectively. The
derived distance agrees with the literature, including the {\it 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 $R_\mathrm{V}=3.60\pm0.05$ and
$A_\mathrm{V}=0.20\pm0.02$ 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.
