The exceptionally high luminosities of gamma-ray bursts (GRBs), gradually emerging as extremely useful probes of star formation, make them promising tools for exploration of the high-redshift Universe. Here we present a carefully selected sample of Swift GRBs, intended to estimate in an unbiased way the GRB mean redshift (z_mean), constraints on

We report on the properties of a 99.3-d periodic modulation in the X-ray transient XTEJ1716-389. We associate this source with the transient KSJ1716-389, first detected by the Mir/Kvant module in 1994. The spectral characteristics of XTEJ1716-389, a high intrinsic absorption column, strong emission features and a power-law spectrum, make it very

We undertook a time-series photometric multisite campaign for the rapidly oscillating Ap (roAp) star HD 99563 and also acquired mean light observations over four seasons. The pulsations of the star, which show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 μHz and some first harmonics of it. The

We report the counterpart to the X-ray transient and black hole candidate XTE J1817-330 (ATEL #714). Our observations consist of a series of 5s and 10s g'-band images obtained with the 6.5m Magellan Clay telescope during 2006 Feb 10 09:23-09:42 UT using the multi-object imaging spectrograph LDSS-3. The frames were acquired with an image quality of

A detailed analysis of a large collection of electronic spectra from three observatories, together with radial velocities published earlier, were used to derive a new ephemeris and improved orbital elements for the ɛ Per binary. Observations covering a time interval of about 37 000 days (101.3 years) can be reconciled with a constant orbital period

We demonstrate that the mass of the most massive star in a cluster correlates non-trivially with the cluster mass. A simple algorithm, according to which a cluster is filled up with stars that are chosen randomly from the standard initial mass function (IMF) but sorted with increasing mass, yields an excellent description of the observational data