Ultra Luminous X-ray Sources (ULXs) are extragalactic X-ray point sources with L_X ˜ 10^39-10^41 erg s^-1 discovered in the 80s with the Einstein satellite and confirmed as black hole X-ray binaries during the last decade. The nature of the compact object is highly controversial. They could be super-Eddington stellar-mass black holes or

The use of deep blank fields is crucial for the correct operation of the GTC. Hitherto, the list of deepest blank fields was the compilation by M. Azzaro for the ING telescope. However, they demonstrated to be shallow for large class telescopes. We used TESELA, a new VO tool, to determine blank fields for their use with OSIRIS at the GTC. The

Taking advantage of the Virtual Observatory, we have searched for deep blank fields (DBFs) throughout the whole sky, with a minimum size of 10' diameter and an increasing threshold magnitude from 15 to 18 in USNO-B R band. The result is the catalogue with the deepest blank fields known so far. Some of them have been tested with the 10.4m GTC

Context. In a probabilistic framework of the interpretation of the initial mass function (IMF), the IMF cannot be arbitrarily normalized to the total mass, ℳ, or number of stars, N, of the system. Hence, the inference of ℳ and N when partial information about the studied system is available must be revised (i.e., the contribution to the total

Context. Our understanding of stellar systems depends on the adopted interpretation of the initial mass function, IMF φ(m). Unfortunately, there is not a common interpretation of the IMF, which leads to different methodologies and diverging analysis of observational data. Aims: We study the correlation between the most massive star that a cluster