We present results of an extensive study of the X-ray spectral properties of sources detected in the RIXOS survey, which is a large, nearly complete sample of objects detected serendipitously in ROSAT PSPC fields down to a flux limit of 3x10^-14ergcm^-2s^-1 (0.5-2keV). We show that for X-ray surveys containing sources with low count rate, such as

Context. Variability is a general property of active galactic nuclei (AGN). The way in which these changes occur at X-rays is not yet clearly understood. In the particular case of low-ionization nuclear emission line region (LINER) nuclei, variations on the timescales from months to years have been found for some objects, but the main driver of

IAUC 7498 available at Central Bureau for Astronomical Telegrams.

A bright X-ray transient in M31 was detected in a 5000-sec Chandra ACIS-I observation on 2001 Aug 31.54 UT. The new transient (CXOU J004305.5+411703) is located at R.A. = 00h43m05s.55, Decl = +41o17'03''.3 (equinox 2000.0; based on the aspect solution, with uncertainty of ~1''). The energy spectrum can be fitted with a power-law model with a photon

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We present the first chemical composition study of two unevolved stars in the globular cluster NGC 2808, obtained with the X-shooter spectrograph at VLT. NGC 2808 shows three discrete, well-separated main sequences. The most accepted explanation for this phenomenon is that their stars have different helium contents. We observed one star on the