We present an IZ photometric survey covering a total area of about 1000 arcmin2 around the ɛ Orionis young massive star (˜10 Myr, d=412 pc) and reaching a limiting magnitude I=22. From the resulting I, I-Z color-magnitude diagram we have selected 123 red candidates in the interval I=15--22 mag, which according to evolutionary models corresponds to

The primordial abundance of 4He, YP, is one of the hottest themes in present-day astronomy, mostly due to its cosmological relevance. The disagreement between different determinations has been currently reduced to the 1-2% level, but these differences are still large enough to have deep implications for Big-Bang nucleosynthesis. It is therefore

We present J-H-K' photometry for a sample of 45 high redshift quasars found by the Sloan Digital Sky Survey. The sample was originally selected on the basis of optical colors and spans a redshift range from 3.6 to 5.03. Our photometry reflects the rest-frame SED longward of Lyalpha for all redshifts. The results show that the near-IR colors of high

We explore a scenario in which metal-poor globular clusters (GCs) are enriched by the first supernovae in the universe. If the first stars in a 107 Msolar dark halo were very massive (>180 Msolar), then a pair-instability supernova from a single massive star could produce sufficient iron to enrich 106 Msolar of pristine, primordial gas to [Fe/H]~-2

The analysis of emission line region of Seyfert 1 galaxy Mrk 817 is presented. We found that emission line region in Mrk 817 is very complex. Moreover, the Narrow Line Region shows complex structure. The spectral line shapes of Mrk 817 indicates at least three kinematically separated regions, one (or more) which emits the broad line component (V

The NLTE Fe I line formation problem in a three-dimensional granulation model of the metal-poor halo star HD 140283 is considered. The self-consistent solutions of the kinetic and radiative transfer equations were obtained with a realistic atomic model Fe I + Fe II. The effects of horizontal radiative transfer are neglected. The near-UV