The distance to NGC 5904 (M 5) via the subdwarf main sequence fitting method

Abstract

We present a determination of the distance modulus of the globular cluster NGC 5904 (M 5), obtained by means of the subdwarf main-sequence fitting on the (V,V-I) color-magnitude diagram. The subdwarf sample has been selected from the HIPPARCOS catalog in a metallicity range homogeneous with the cluster ([Fe/H] ≃ -1.1). Both the cluster and the subdwarfs have been observed with the same telescope+instrument+filters setup (namely, ESO-NTT equipped with the SUSI2 camera), in order to preserve homogeneity and reduce systematic uncertainties. A set of archival HST data has then been used to obtain a deep and precise ridge line. These have been accurately calibrated in the ground photometric system by using the NTT data and used to fit the cluster distance modulus. By adopting the most commonly accepted values for the reddening, E(B-V) = 0.035 and 0.03, we obtain respectively μ₀ = 14.44 ± 0.09 ± 0.07 and μ₀ = 14.41 ± 0.09 ± 0.07, in agreement with recent determinations.

Based on data collected at ESO-La Silla, Chile, (GTO 63.L-0717) and from HST archival data (GO 8310).