M. Tarenghi

The VLT Interferometer: a unique instrument for high-resolution astronomy

The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion in this year when the fourth of the 8-m Unit Telescopes will see first light. At the same time, the preparation for first fringes of the VLT Interferometer (VLTI) is advancing rapidly with the goal of having the first fringes with two siderostats within this year. In this article we describe the status of the VLTI and its subsystems, we discuss the planning for first fringes with the different telescopes and instruments. Eventually, we present an outlook for the future of interferometry with Very Large Telescopes.

The VLTI – A Status Report

The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion. After the four 8-m Unit Telescopes (UT) individually saw first light in the last years, two of them were combined for the first time on October 30, 2001 to form a stellar interferometer, the VLT Interferometer. The remaining two UTs will be integrated into the interferometric array later this year. In this article, we will describe the subsystems of the VLTI and the planning for the following years.

ESO VLT laser guide star facility

We report in this paper on the design and progress of the ESO Laser Guide Star Facility. The project will create a user facility embedded in UT4, to produce in the Earths Mesosphere Laser Guide Stars, which extend the sky coverage of Adaptive Optics systems on the VLT UT4 telescope. Embedded into the project are provisions for multiple LGS to cope with second generation MCAO instruments.

VLT observations of comet 46P/Wirtanen

Comet 46P/Wirtanen, prime target of ESAs ROSETTA mission, was successfully observed at the Very Large Telescope Observatory in Chile: on 17 May 1999 with the Test Camera at the Cassegrain focus of the 8.2-m VLT Kueyen telescope and on 8 December 2001 with FORS1 at Unit Telescope 4 Yepun. May 1999: no coma was detected at heliocentric distance r = 4.98 AU. From the measured brightness in the Bessell R-filter, a mean nucleus radius of 555 ′ 40 m is derived (for a geometric albedo of 0.04 and a phase darkening of 0.04 mag/deg). The nucleus signal varies during the 2.7 h observing interval and a peak-to-peak amplitude of ∼0.38 mag is determined. The measured lightcurve is in agreement with a rotation period of 6-7.5 hours and a ratio of the main nucleus axes of at least 1.4. The non-detection of a coma allows one to put an approximate upper limit for Afp of <0.45 cm (suggesting a dust production rate of 0.05 kg/s). December 2001: a weak and condensed coma seems to be present in the seeing disk of the comet at 2.9 AU inbound, causing a higher brightness than expected from the previous size estimates of the nucleus. The colour of the comet appears very red (V - R spectral gradient ∼47%/100 nm). The Afp value of the comet was 6.5 ′ 2 cm (equivalent to a dust production rate of about 1 kg/s).

The VLT Interferometer

One of the observing modes available with the ESO Very Large Telescope will be coherent combination of the light received by up to four 8m unit telescopes and several 1.8m auxiliary telescopes. The location of the main telescopes is fixed, while auxiliary telescopes can be moved among some 30 observing stations. The locations of these stations were chosen to augment the (µ, υ) coverage of the unit telescopes as well as to function as an independent interferometric array.

The VLT laser guide star facility

We report on the ongoing VLT Laser Guide Star Facility project, which will allow the ESO UT4 telescope to produce an artificial reference star for the Adaptive Optics systems NAOS-CONICA and SINFONI. A custom developed dye laser producing >10W CW at 589nm is installed on-board of the UT4 telescope, then relayed by means of a single mode optical fiber behind the secondary mirror, where a 500mm diameter lightweight, f/1 launch telescope is projecting the laser beam at 90 km altitude. We described the design tradeoffs and provide some details of the chosen subsystems. This paper is an update including subsystems results, to be read together with our previous paper on LGSF design description.

VLTI program: a status report

The VLTI (Very Large Telescope Interferometer) is one of the operating modes of the VLT, presently being built on Cerro Paranal, Chile. It aims at providing access to an observing mode at very high angular resolution and very high sensitivity (with respect to the currently operating astronomical interferometers). After a long period of conceptual, then detailed, studies, ESO is starting to build and to procure the main components of the interferometer in order to open this unpaired observing facility by the turn of the century.

A study of the large-scale distribution of galaxies in the South Galactic Pole region – I. The data

We present the data from an extensive, moderately deep (b_J = 19.5) spectroscopic survey of

A study of the large-scale distribution of galaxies in the South Galactic Pole region — II. Further evidence for a preferential clustering scale?

\sim 600

Scientific objectives of ESO's PRIMA facility

galaxies within four regions of sky located near the South Galactic Pole. About 75% of the measured galaxies are in a 3deg x 1.5deg region dominated by the rich cluster Klemola 44 (Abell 4038). The other three smaller areas cover about 1 square degree each. Here we discuss in detail the observing and data reduction strategies, the completeness and errors on the measured redshifts. The data collected are being used for: (1) a study of the large--scale redshift distribution of the galaxies in each field, and (2) a thorough dynamical investigation of Klemola 44. Results from these analyses will be presented in forthcoming papers.