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Aims: We present the results of an analysis of 107 extremely metal-poor (EMP) stars with metallicities lower than [Fe/H] =- 3.0, identified in medium-resolution spectra in the Sloan Digital Sky Survey (SDSS). Our analysis provides estimates of the stellar effective temperatures and surface gravities, as well as iron, calcium, and magnesium

We present deep images in H alpha +[NII] and [OIII] lambda 5007 of the region around NGC 7027 obtained with the wide field camera (WFC) at the Isaac Newton Telescope (INT). We observe the complex structure of the interstellar medium where the planetary is projected and identify a large spherically symmetric structure around the planetary nebula. A

CLUSTERS of galaxies are the largest gravitationally bound systems in the Universe and therefore provide important constraints on the formation and evolution of large-scale structure. Cluster evolution can be inferred from observations of the X-ray emission of the gas in distant clusters, but interpreting these data is not straightforward. In a

We present the results of the multisite differential CCD photometry for the two delta Scuti stars, BN and BV Cnc, in the open cluster Praesepe. The main objective was to identify the character of the pulsation modes in BN Cnc deriving their accurate periods, amplitudes and phases. These parameters are essential for the mode identification which

The variation of the electron density with position in a selected group of bright giant extragalactic H II regions has been studied using long slit spectrophotometry at high spectral and spatial resolution. Density values for the ionized gas of the regions have been obtained from the measurement of the forbidden S II 6717, 6731 A ratio. It is