BD+53°2790, an O9.5V star, is the optical counterpart to the HMXRB 4U 2206+54. This system was classified initially as a BeX, but observational evidence soon stressed the need to revise this classification. The permanent asymmetry in the H α line profiles (in contrast with the cyclic variations shown by Be stars), the variations in the profile of

The aim of this work is to make available unpublished non-Fe+ emission line fluxes from optical spectra of the symbiotic nova RR Tel, which were taken in 2000, and to compare them with fluxes of the same lines from spectra taken in 1996. After leaving out blends and misidentifications, as well as the unreliable far-red and violet lines, we present

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Aims: We try to identify ultra-cool dwarfs from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with SDSS i-z and r-z colors. We also obtain proper motion data from SDSS, 2MASS, and UKIDSS and improve spectral typing from SDSS and 2MASS photometric colors. Methods: We selected ultra-cool dwarf candidates from the SDSS DR7 with

Polarized light provides the most reliable source of information at our disposal for diagnosing the physical properties of astrophysical plasmas, including the three-dimensional (3D) structure of the solar atmosphere. Here we formulate and solve the 3D radiative transfer problem of the linear polarization of the solar continuous radiation, which is

A new method to obtain the thermodynamic coefficients in an analytic and exact form for applications in radiative and convective transport in thermodynamic equilibrium for stellar atmosphere and plasma spectroscopy is developed. The resulting exact expressions are formed by sums of the degrees of ionization of the components of the system