Aims: We develop an accurate and general semi-classical formalism that deals with the definition and the calculation of the collisional depolarizing constants of the levels of simple and complex singly-ionized atoms in arbitrary s-states perturbed by collisions with hydrogen atoms. The case of ions with hyperfine structure is investigated fully

We report on time-resolved optical spectroscopy of 10 non-eclipsing nova-like cataclysmic variables in the orbital period range between 3 and 4 h. The main objective of this long-term programme is to search for the characteristic SWSextantis behaviour and to eventually quantify the impact of the SWSex phenomenon on nova-likes at the upper boundary

In this paper we characterize the congruence associated to the direct sum of all irreducible representations of a finite semigroup over an arbitrary field, generalizing results of Rhodes for the field of complex numbers. Applications are given to obtain many new results, as well as easier proofs of several results in the literature, involving

We report on the detection of two Hα-emitting extremely compact objects from deep images of the A634 and A539 clusters of galaxies at z~0.03. Follow-up long-slit spectroscopy of these two unresolved sources revealed that they are members of their respective clusters, showing H II-type spectra. The luminosity and the extreme equivalent width of Hα +

Multi-object spectroscopic observations of A697 were carried out at the TNG telescope in December 2003 during the program of proposal AOT8/CAT-G6. (1 data file).

By detecting ionised-gas emission in 75% of the cases, the SAURON integral-field spectroscopic survey has further demonstrated that early-type galaxies often display nebular emission. Furthermore, the SAURON data have shown that such emission comes with an intriguing variety of morphologies, kinematic behaviours and line ratios. Perhaps most