Characterization of 15 overlooked Ruprecht clusters with ages within 400 Myr and 3 Gyr

We derive fundamental, structural and photometric parameters of 15 overlooked Ruprecht (hereafter Ru) star clusters by means of Two-Micron All-Sky Survey photometry and field-star decontamination. Ru 1, 10, 23, 26, 27, 34, 35, 37, 41, 54, 60, 63, 66 and 152 are located in the third Galactic quadrant, while Ru 174 is in the first. With the constraints imposed by the field-decontaminated colour–magnitude diagrams and stellar radial density profiles (RDPs), we derive ages in the range 400 Myr – 1 Gyr, except for the older Ru 37, with ∼3 Gyr. Distances from the Sun are within 1.5 ≲ d⊙ (kpc) ≲ 8.0. The RDPs are well-defined and can be described by a King-like profile for most of the radial range, except for Ru 23, 27, 41, 63 and 174, which present a conspicuous stellar density excess in the central region. The clusters dwell between (or close to) the Perseus and Sagittarius-Carina arms. We derive evidence in favour of cluster size increasing with distance to the Galactic plane (ZGP), which is consistent with a low frequency of tidal stress associated with high-|ZGP| regions. The clusters are rather faint even in the near-infrared, with apparent integrated J magnitudes within 6.4 ≲mJ≲ 9.8, while their absolute magnitudes are −6.6 ≲MJ≲−2.6. Extrapolation of the relation between MV and MJ, derived for globular clusters, suggests that they are low-luminosity optical clusters, with −5 ≲MV≲−1.