We report on an observing campaign in 2001 March to monitor the brightness of the later arriving Q0957+561B image in order to compare with the previously published brightness observations of the (first-arriving) A image. The 12 participating observatories provided 3543 image frames, which we have analyzed for brightness fluctuations. From our

We have acquired new time series photometry of the two pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 with the Whole Earth Telescope. Additional single-site photometry is also presented. We use all these data plus all available archival measurements to study the temporal behaviour of the pulsational amplitudes and frequencies of

We present the discovery of three new quasars at z>6 in ~ 1300 deg2 of Sloan Digital Sky Survey imaging data, J114816.64+525150.3 (z=6.43), J104845.05+463718.3 (z=6.23), and J163033.90+401209.6 (z=6.05). The first two objects have weak Lyα emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate

Dwarf satellite galaxies undergo strong tidal forces produced by the main galaxy potential. These forces disturb the satellite and produce asymmetries in its stellar distribution, tidal tail formation, and modifications of the velocity dispersion profiles. Most of these features are observed in the Ursa Minor (UMi) dwarf spheroidal galaxy, which is

Recently, a new class of type I X-ray bursters was suggested, the ``burst-only sources'', i.e. detected only during an X-ray burst, and no persistent emission around the burst. Short follow-up observations of several burst-only sources could not unambiguously identify the X-ray burster, but suggested that they were at luminosities comparable to

The Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) is an imaging system and a low-resolution long-slit and multi-object spectrograph for the 10.4m Spaninsh telescope GTC. OSIRIS spectral range (from 365 up to 1000 nm) and observing modes require a wide set of elements in order to provide imaging and spectroscopic