Fundamental parameters of the moderately young open clusters NGC 5999, NGC 6031, Ruprecht 115 and Ruprecht 120

We present CCD BVI Johnson-Cousins photometry for the southern open clusters NGC 5999, NGC 6031, Ruprecht 115 and Ruprecht 120. The sample consists of about 1160 stars reaching down to V ~ 19 mag. From the analysis of the colour-magnitude diagrams, we confirm the reality of the clusters and derive their fundamental parameters (reddening, distance and age). We also present integrated spectra for NGC 6031, Ruprecht 115 and Ruprecht 120, covering a range from 3500 to 9200 A. From the equivalent widths of Balmer and infrared Ca ii triplet lines, as well as from a comparison of the obtained spectra with those of template clusters, we derive reddening, age and metallicity. The photometric and spectroscopic results allow us to conclude that the four clusters are moderately young (age &sim 100-500 Myr) and are located approximately towards the Galactic Centre at ~ 2.3 kpc from the Sun. NGC 6031 and Ruprecht 120 have nearly solar metal content, while Ruprecht 115 appears to be slightly metal-rich.