Following the announcement of a new period of activity of the soft gamma-ray repeater SGR 1806-20 in 1996 November, we have performed follow-up observations of the IR counterpart, which has been proposed as a luminous blue variable or B[e] star. We have found that no variability larger than 0.1 mag in the K-band is present in the data. No variation

We examine the status of the threat posed to stellar-mass black hole candidates by the possible existence of Q-stars (compact objects with an exotic equation of state that might have masses well above the normally accepted maximum for standard neutron stars). We point out that Q-stars could be extremely compact (with radii less than 1.5 times the

We present new results from a study of recent cosmic microwave background (CMB) observations which provide the first strong evidence for the existence of a 'Doppler peak' localized in both angular scale and amplitude. This first estimate of the angular position of the peak is used to place a new direct limit on the curvature of the universe

We checked the change of the effective temperature with the atmospherical pulsation of rho Cas from combined analyses of optical spectra of 1993-95 and IUE spectra of 1979-81. We find an upper range for bigtriangleup T_eff =~ 750 K over a period of 16-17 months. We present a thorough study of the related absorption line profile changes from which a

The recent result obtained by Givens and Kostinski [J. Mod. Opt. 40, 471 (1993)] successfully solves the old and important problem in polarization optics of characterizing a given 4×4 matrix as a Mueller matrix from a mathematical point of view. For practical purposes, however, a further elaboration on this result is needed, namely, the problem of

The radial scale length of the exponential component of the disc of the Milky Way has been determined in the near infrared. We have used the TMGS (Two Micron Galactic Survey) database which contains positions and K-magnitudes of about 700.000 stars distributed in serveral regions along the galactic plane. From those we have selected areas more than