We present spectroscopic observations of the black hole binary V4641 Sagittarii, obtained between 2004 July 4 and 2005 March 28, which cover the minor outburst of the star in early 2004 July and quiescence variations on 19 nights scattered over six months. During the outburst, the star peaked approximately 3 mag brighter than usual, and our spectra

We derive an exact solution (in the form of a series expansion) to compute gravitational lensing magnification maps. It is based on the backward gravitational lens mapping of a partition of the image plane in polygonal cells (inverse polygon mapping, IPM), not including critical points (except perhaps at the cell boundaries). The zeroth-order term

We present deep broadband R and narrowband Hα images of Stephan's Quintet. The observations in the R band show that the diffuse halo of Stephan's Quintet is larger than previously thought and extends out to NGC 7320C. However, we have not found emission connecting NGC 7331 and NGC 7320 to R~26.7 mag arcsec-2 (at more than a 3 σ level), so there is

We present the results of a 9.3-deg2 infrared (ZYJHK) survey in the Upper Scorpius association extracted from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey Early Data Release. We have selected a total of 112 candidates from the (Z - J,Z) colour-magnitude diagram over the Z = 12.5-20.5 magnitude range, corresponding to M = 0.25

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