This thesis has been dedicated to the study of Galaxy Clusters as Cosmological tools. The work is divided into two main parts; the first is purely observational, whereas the second is dedicated to the preparation of tools for cosmological analyses. The observational section has been developed within the frame of the optical validation program

The relatively small family of ultra-compact X-ray binary systems is of great interest for many areas of astrophysics. We report on a detailed X-ray spectral study of the persistent neutron star low-mass X-ray binary 1RXS J170854.4-321857. We analysed two XMM-Newton observations obtained in late 2004 and early 2005 when, in agreement with previous

Recent studies have indicated that triple-star systems may play a role in the formation of an appreciable number of planetary nebulae, however, only one triple central star is known to date (and that system is likely too wide to have had much influence on the evolution of its component stars). Here, we consider the possibility that Sh 2-71 was

IGR J17062-6143 is an ultracompact X-ray binary (UCXB) with an orbital period of 37.96 min. It harbours a millisecond X-ray pulsar that is spinning at 163 Hz and and has continuously been accreting from its companion star since 2006. Determining the composition of the accreted matter in UCXBs is of high interest for studies of binary evolution and

Context. The TESS and PLATO missions are expected to find vast numbers of new transiting planet candidates. However, only a fraction of these candidates will be legitimate planets, and the candidate validation will require a significant amount of follow-up resources. Radial velocity (RV) follow-up study can be carried out only for the most