The evolution of the morphology of C/1999 S4 (LINEAR) is examined from a series of images taken from shortly before the disruption of the nucleus until 10 days afterwards. This is combined with light curve data to provide a unique documentation of the early evolution of the disruption event. Neither images from the 1-m Jacobus Kapteyn Telescope nor

We provide constraints on the AGN contribution to the mid-IR extragalactic background light from a correlation analysis of deep X-ray and mid-IR observations in two regions centred on the Lockman Hole and Hubble Deep Field North (HDF-N). The Lockman region, of more than 200 square arcminutes, was observed by ISOCAM and XMM-Newton to a depth of 0.3

The goal of this work is two-fold. In the first part of this paper we regard classical Plebanski's action as a BF action supplemented by constraints. We introduce a spin foam model for Riemannian general relativity by systematically implementing these constraints as restrictions on paths in the state-sum of the BF theory. The spin foam model

Amateur astronomers have always represented an important observing group in cometary astronomy. Much of our knowledge of cometary light curves has come from amateur data, initially in the form of total visual magnitude estimates and now increasingly in the form of CCD observations. The increasingly widespread use by amateur astronomers of CCD

We have observed the spectrum of Procyon A (F5 IV) from 4559 to 5780 Å with a signal-to-noise ratio of ~103 and a resolving power of 2×105. We have measured the line bisectors and relative line shifts of a large number of Fe I and Fe II lines, comparing them to those found in the solar spectrum. A three-dimensional hydrodynamical model atmosphere

Within the framework of the European Space Agency (ESA) SILEX project, aimed at experimentally demonstrating the feasibility of inter-satellite optical communications links, an Optical Ground Station (OGS) has been built by ESA in the premises of the Instituto de Astrofisica de Canarias (IAC, Institute of Astrophysics of the Canary Islands)