A survey of interstellar Na I D1 and D2 absorption features found in the spectra of 31 early-type stars in the first and fourth Galactic quadrants reveals a new picture of the large-scale kinematics of interstellar gas in the vicinity of the Sun. While absorption features found in the spectra of stars in the fourth Galactic quadrant show the gas

BP Tau is one of the few classical T Tauri stars for which the presence of a hot spot in the surface has been reported without ambiguity. The most likely source of heating is gravitational energy released by the accreting material as it shocks with the stellar surface. This energy is expected to be radiated mainly at UV wavelengths. In this work we

The three major spiral galaxies in the Local Group are known to be warped. The question is investigated of whether or not these three warps are aligned. Using available HI observations we find that they are noticeably aligned. Vectors defining the warp orientation form the following angles: [M 31, M 33]=33°; [M 31, Milky Way]=35°; [M 33, Milky Way]

We compare schematic modeling of spots and plage on the surface of cool dwarfs with Pleiades data to assess effects of magnetic activity on the strengths of the LiI and KI resonance lines in Pleiades spectra. Comprehensive LiI and KI NLTE line formation computation is combined with comparatively well-established empirical solar spot and plage

We present the first results of our program of spectroscopic observations with orbital phase resolution of short-period active binaries. We have collected simultaneous data in the lines Hα, Hβ, and the infrared triplet (IRT) of Ca II (8498 and 8542 A). In this paper we discuss the methods used to analyze the spectra and describe the results

We describe and apply the methods that have been developed to calibrate the Advanced Stokes Polarimeter and to compensate for the polarization effects introduced by the Vacuum Tower Telescope at the National Solar Observatory/Sunspot. A seven-parameter model of the telescope is fitted to data obtained at a variety of mirror angles using