High-resolution optical spectra of the ultra-luminous X-ray source (ULX) NGC 5408 X-1 show a broad component with a width of ~750 km s-1 in the He II and Hβ lines in addition to the narrow component observed in these lines and [O III]. Reanalysis of moderate-resolution spectra shows a similar broad component in the He II line. The broad component

Accurate model stellar fluxes are key for the analysis of observations of individual stars or stellar populations. Model spectra differ from real stellar spectra due to limitations of the input physical data and adopted simplifications, but can be empirically calibrated to maximize their resemblance to actual stellar spectra. We describe a least

We present the first results on the bremsstrahlung emission of photons accompanying ternary spontaneous fission of the 252Cf nucleus. We also compare our calculations on the basis of quantum model with preliminary experimental data and find a good agreement between theory and experiment for photon energies up to 500 keV, when the α-particle

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Companions exert adverse effects on the relationships valid for Cepheids. Physical companions may also cause observable effects (e.g., phase jump in the pulsation, slight excitation of non-radial modes). Many new binaries among Cepheids can be revealed by using radial velocity measurements to be made by Gaia and by deriving astrometric orbit from

We report spectroscopic observations for 19 δ Sct candidates observed by the Kepler satellite both in long and short cadence mode. For all these stars, by using spectral synthesis, we derive the effective temperature, the surface gravity and the projected rotational velocity. An equivalent spectral-type classification has been also performed for