ar X iv : a st ro - p h / 98 09 06 4 v 1 5 S ep 1 99 8 Velocity Dispersion of the Gravitational Lens 0957 + 561 1

ar X iv : a st ro - p h / 96 06 15 5 v 2 6 S ep 1 99 6 Comment on “ Dispersion Velocity of Galactic Dark Matter Particles ”

ar X iv : a st ro - p h / 98 09 06 1 v 1 4 S ep 1 99 8 The magnification invariant of simple galaxy lens models

We demonstrate that for several of the gravitational lens models used to describe galaxies, there exists a quantity we dub the magnification invariant, equaling the sum of the signed magnifications of the images, that is a constant when the image multiplicity is a maximum. This invariant is independent of most of the model parameters, and is independent of the source position as long as the sou...

ar X iv : a st ro - p h / 98 02 06 3 v 1 5 F eb 1 99 8 The Redshift Distribution of Distant Sources from Gravitational Depletion in Clusters

Gravitational lensing can be used to analyze the redshift distribution of faint galaxies. In particular the magnification bias modifies locally the galaxy number density of lensed sources observed in lensing clusters. This depletion area probes the redshift distribution of galaxies beyond B = 25. In this proceedings I present this new tool to infer the redhsift distribution of faint galaxies.

ar X iv : a st ro - p h / 98 07 09 0 v 1 9 J ul 1 99 8 1 MACROSCOPIC PROCESSES IN THE SOLAR INTERIOR

With the

ar X iv : a st ro - p h / 02 05 39 9 v 1 2 3 M ay 2 00 2 A Large Brightness Enhancement of the QSO 0957 + 561 A Component

We report an increase of more than 0.2 mag in the optical brightness of the leading image (A) of the gravitational lens Q0957+561, detected during the 09/2000 – 06/2001 monitoring campaign (2001 observing season). The brightening is similar to or even greater than the largest change ever detected during the 20 years of monitoring of this system. We discuss two different provisional explanations...