A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In the Southern Hemisphere (WISH) survey

The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the observations, the survey has a much lower resolution in declination than in right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS shows that the positional accuracy is less constrained in declination than in right ascension, but there is no significant systematic error. We present a source list containing 73570 sources. We correlate this WISH catalogue with the NVSS to construct a sample of faint Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies with large optical telescopes in the southern hemisphere. This sample is aimed at increasing the number of known high redshift radio galaxies to allow detailed follow-up studies of these massive galaxies and their environments in the early Universe.Comment: 12 Pages, including 5 PostScript figures. Accepted for publication in Astronomy & Astrophysics. The full WISH catalog with 73570 sources is available from http://www.strw.leidenuniv.nl/wenss

The relative photometric lightcurve of UM673 A&B

From 1987 to 1993, we have carried out at ESO a photometric monitoring of the gravitationally lensed quasar UM673. The main result is that the two lensed images of UM673 did not show any significant relative variation during more than five years

A search for gravitational lensing among highly luminous quasars - Observational strategy and survey

The observational techniques employed to search for gravitational lensing effects in highly luminous quasars (HLQs) are given, along with results of the observations. The program, begun in 1986, considers the visible and dark matter distributions at different scales in the universe to determine which extragalactic objects are gravitationally lensed. The Hubble parameter and galaxy masses are determined from the observations, and observations of microlensing effects provide data on HLQ size and structures. The redshifts are found to be between 1 and 3.6, with apparent visual magnitudes 16-18.5 and absolute visual magnitudes between -29 and -30.6. About one quarter of the images exhibit either multiple components, elongated structures, jetlike features, or faint nearby galaxies. The double quasar UM 673 and its 'overlying' lens galaxy is given as a prime example of an HLQ that is gravitationally lensed. It is theorized many more HLQs are gravitationally lensed, and specific future observations are recommended

The cloverleaf quasar H1413+117: a preliminary light curve

The cloverleaf quasar H1413+117 was discovered to be a gravitational lens system in 1988. Since then, it has been photometrically monitored essentially as part of the ESO key-program Gravitational lensing: we present here a first preliminary lightcurve for its four individual images

Photometric monitoring (1987 to 1994) of the gravitational lens candidate UM 425.

We present the results of a 7 year long photometric monitoring of two components (A and B) of UM 425, thought to be images, separated by 6.5", of the same z=1.47 quasar. These components have been imaged through an R filter in order to obtain their light curves. The photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component. The brightest image (component A, m_R_=15.7) shows a slow and smooth increase in brightness of 0.2 magnitude in seven years, while the faintest one (component B, m_R_=20.1) displays an outburst of 0.4 magnitude which lasts approximately two years. The variation of component B may be interpreted in two ways, assuming UM 425 is gravitationally lensed. If it is due to an intrinsic variation of the quasar, we derive a lower limit of 3 years on the time delay from the fact that it is not observed in component A. On the other hand, if it is a microlensing "High Amplification Event", we estimate the size of the source to be ~10^-3^pc, in agreement with standard models of AGNs. These observations are consistent with the gravitational lens interpretation of the object. Furthermore, all the CCD frames obtained under the best seeing conditions have been co-added, in an attempt to detect the deflector. The final R image reveals a rich field of faint galaxies in the magnitude range m_R_~22-24. No obvious deflector, nor any system of arcs or arclets is detected, down to a limiting magnitude of m_R_~24

Profiles of a Key Programme: Gravitational Lensing

Prior to Professor van der Laan's enquiry, in the March 1988 issue of the Messenger, on the general interest among astronomers from the European community to possibly participate in Key Programmes (KPs) at the European 80uthern Observatory, at least three distinct groups (including more than half of the above authors) were already involved in the study of "gravitational lensing" effects (see box on pages 10-11). Observations were being performed with the help of various telescopes on La 8illa as weil as at other observatories (VLA, CFHT, Palomar, Kitt Peak, etc.)

ESO & NOT photometric monitoring of the Cloverleaf quasar

The Cloverleaf quasar, H1413+117, has been photometrically monitored at ESO (La Silla, Chile) and with the NOT (La Palma, Spain) during the period 1987--1994. All good quality CCD frames have been successfully analysed using two independent methods (i.e. an automatic image decomposition technique and an interactive CLEAN algorithm). The photometric results from the two methods are found to be very similar, and they show that the four lensed QSO images vary significantly in brightness (by up to 0.45 mag), nearly in parallel. The lightcurve of the $D$ component presents some slight departures from the general trend which are very likely caused by micro-lensing effects. Upper limits, at the 99% confidence level, of 150 days on the absolute value for the time delays between the photometric lightcurves of this quadruply imaged variable QSO, are derived. This is unfortunately too large to constrain the lens model but there is little doubt that a better sampling of the lightcurves should allow to accurately derive these time delays. Pending a direct detection of the lensing galaxy (position and redshift), this system thus constitutes another good candidate for a direct and independent determination of the Hubble parameter. Based on observations collected at the European Southern Observatory (La Silla, Chile) and with the Nordic Optical Telescope (La Palma, Spain). Table 1. Logbook for the ESO and NOT observations together with photometric results for the Cloverleaf quasar. This long table can be accessed on the WWW at the URL address: http://vela.astro.ulg.ac.be/grav_lens/glp_homepage.html

ESO key programme, gravitational lensing: quasars and radio galaxies; a status report

The scientific background and objectives of our ESO Key Programme are first recalled. A brief account of our research activities (observing runs at ESO and elsewhere, meetings, etc.) is then given. Preliminary scientific results are presented concerning 1) our observational database for highly luminous quasars and distant powerful radiogalaxies; 2) speckle observations of highly luminous quasars; 3) the photometric monitoring and 4) detailed studies of several known gravitational lenses; 5) optical observations of 3C and 4C radio galaxies and 6) of the well known Einstein ring MG 1131+0456

quasar

ESO &amp; NOT photometric monitoring of the Cloverlea