We conducted spectroscopic studies of both components of the visual binary HR 1847 to determine its basic physical and orbital parameters. New observations of this system were obtained using the Ondřejov and Rozhen 2-m telescopes. Radial velocities were measured using the individual spectra and then analysed using the FOTEL code to determine

Aims: We present optical photometry and spectroscopy of the afterglow and host galaxy of gamma-ray burst GRB 040924. This GRB had a rather short duration of T90 ~2.4 s, and a well sampled optical afterglow light curve. We aim to use this dataset to find further evidence that this burst is consistent with a massive star core-collapse progenitor

Aims: In this paper we analyze the spectra of a sample of asteroids in cometary orbits (ACOs) in order to understand the relationship between them, the Jupiter family comets (JFCs), and the outer main belt populations, such as Hilda, Trojan and Cybele asteroids. Methods: We obtained visible (0.55-0.90 μm) and/or near-infrared (0.8-2.3 μm) spectra

Optical microvariability (OM, small amplitude variations in time scales from minutes to hours) in radio-quiet quasars (RQQ) may be as frequent as in radio-loud quasars (RLQ) (de Diego et al. 1998; Ramírez et al. 2007). However, observations cannot still establish the origin of OM.

As part of our ongoing investigation of magnetic activity in ultracool dwarfs we present simultaneous radio, X-ray, UV, and optical observations of LSR1835+32 (M8.5), and simultaneous X-ray and UV observations of VB10 (M8), both with a duration of about 9 hr. LSR1835+32 exhibits persistent radio emission, and Hα variability on timescales of 0.5-2

We consider a gas of hydrogen atoms illuminated by a broadband unpolarized radiation with zero anisotropy. In the absence of external fields, atomic J-levels are thus isotropically populated. While this condition persists in the presence of a magnetic field, we show instead that electric fields can induce the alignment of these levels. We also show