Paranal Instrumental Package

Status of the (non-VLTI) Instrumental Package

The full complement of first generation general use instrumentation at the VLT will ultimately encompass 11 instruments. One Nasmyth Visitor focus is reserved for standalone innovative instruments brought by external teams and another one is provisionally free after the cancellation of NIRMOS. The status, as of October 2009, of VLT instruments in use or still in their development phase is summarized in the table below.

VLT First Generation Instrumentation
Name Built by Observing Modes Start of operations
ISAAC ESO imaging & long-slit spectroscopy (1-5µm) Apr 99
FORS1/2 Heidelberg, Munich, Göttingen, ESO imaging, MOS*, polarimetry (0.3-1µm) Apr 99/
Apr 00
UVES ESO, Trieste high resolution cross-dispersed spectroscopy (0.3-1 µm) Apr 99
NACO NAOS: ONERA, Paris, Grenoble, ESO adaptive optics system for CONICA Oct 02
CONICA: Heidelberg, Garching, ESO high angular resolution imaging and spectroscopy (1-5µm) Oct 02
FLAMES Paris, Geneva; AAO, ESO MOS* (fibre) & multi IFS** (0.37-1µm) Apr 03
VIMOS Paris, Marseille, Haute Provence, Toulouse, Bologna, Milan, Naples, ESO wide field imaging, MOS*, IFS** (0.37-1µm) Apr 03
VISIR Saclay, ASTRON, ESO imaging & long-slit spectroscopy (8-25µm) Oct 04
SINFONI Garching, ESO adaptive optics-based IFS** (1-2.5µm) Apr 05
CRIRES ESO high resolution echelle spectroscopy (1-5µm) Apr 07
HAWKI ESO high acuity wide field K-band imager Apr 08
* MOS = Multi-Object Spectroscopy, **IFS=Integral Field Spectroscopy

La Silla Observatory instrumentation features many smaller relatives to many VLT instruments, e.g. EFOSC2 and EMMI to FORS and VIMOS, SOFI to ISAAC and FEROS to UVES. There are also unique facilities at La Silla, e.g. the UV-Visible direct imager SUSI2 at the NTT and the extra-solar planet searcher HARPS at the 3.6m telescope.

A number of so-called second generation instruments are presently in preparation by external consortia and/or by ESO. ESO's Scientific Technical Committee has given the first set of recommendations on its meeting in November 2003.

Operational Strategy

The whole VLT operation, from observing proposals to the dissemination of astronomical data, is conceived within a full Data Flow System developed by the ESO Data Management and Operations Division. This, in particular, encompasses a comprehensive calibration plan which is systematically executed by the Paranal Observatory Science Operations (PSO) department for all supported (and used) instrument modes.

All observations at the VLT are carried out by a PSO Telescope and Instrument Operator (TIO). (S)he executes the observing blocks which are submitted by the Observer. Two different observing modes are offered: the conventional "visitor mode", with the astronomer present on the site to lead his/her program, and a "service mode", performed directly by the operator assisted by the Paranal astronomer on duty. 50% of the observations are presently performed in service mode.

An important aspect for the observatory operation is the increased efficiency from "flexible" scheduling of the observations. Many programs require well defined environmental conditions, e.g. extremely good seeing for imaging spectroscopy, very low vapour content for some infrared windows, slow turbulence for observations near the diffraction limit of the telescope with adaptive optics corrections, etc. Flexible scheduling allows such observations to be obtained in an optimum way, with a guaranteed scientific quality. This strategy requires ultimately the full complement of automated, multi-mode instruments. Switching between instruments, when needed, can be achieved with minimal time loss by switching to another focus.

In addition, one Nasmyth focal station remains free for "visitor" instruments. This facility provides fast access for innovative instruments.

An essential part of our observational strategy is to provide means for the applicants to find and select astronomical targets for further studies with the VLT. To that effect and as an interim solution, the WFI wide-field (0.5° x 0.5°) optical camera has been installed at the La Silla 2.2m. telescope. It will be replaced by the 1° x 1° OmegaCAM optical camera, put at the Paranal 2.6m VST. At the present time, our only "wide-field" near-IR searcher is SOFI at the La Silla 3.5m. NTT, with an already respectable 5' x 5' field in the 1 to 2.5µm range. The 4m VISTA facility for Paranal is under development in the UK; it will initialy (ca 2007) offer a very wide-field capability in the near-IR.

Observational Domains

As can be seen on Fig.1 presently planned VLT Instrumentation covers large domains in both Spectral and Spatial Resolution versus Wavelength diagrams. The spectral domain goes from the 0.3µm atmospheric limit to 26µm and the spectral resolution from 10 to 100,000. Spatial coverage varies from the maximum available field at the Nasmyth foci (26 arcmin diameter) to a few arcsec on the sky. Sub-0.1 arcsec spatial resolution is achieved with Adaptive Optics in the 1 to 5µm spectral domain.

An essential ingredient for the performance of the instruments is the use of standardized state of the art detectors and their associated electronics, fully integrated in the VLT data flow. Their status is as follows:


  • Optical Detectors: The CCD detectors and their associated controller systems are directly provided by ESO for all optical instruments. The baseline is 2kx4k 15µm pixels, high quantum efficiency (thinned), very low noise CCDs from EEV and MIT/LL. Read-out noise levels below 2 electrons rms have been achieved on the telescope. The FIERA controller does not limit either the noise or speed performance of present CCDs.


  • Near Infrared Detectors: Nearly all IR arrays and the associated controllers are also provided by ESO. Read-out noise of 3 eelectrons rms for the 1-2.5µm Rockwell Hawaii I and 10 electrons rms for the 1-5µm Raytheon ALADDIN array have been achieved. The IRACE controller does not limit either the noise or speed performance of present arrays.


  • Medium Infrared Detectors: The 8-26µm VISIR arrays were integrated by the consortium, with the IRACE controller provided by ESO.

Spectroscopic Modes

observing modesRecognition that different classes of astronomical objects may have strikingly different spatio-spectral 3-dimensional (apparent) shapes has finally led to the end of the "monopoly" of the long-slit spectrograph, with the deployment of a wide variety of instrument modes, finely tuned to the 3D characteristics of their sought-for targets. The VLT instrumentation package is no exception with its overall ambition of covering efficiently most astronomical objects (see Fig.2 ). The most important classes are:

  • Extended "Continuum" Objects, e.g. Regions of Star Formation, Open and Globular clusters, Nearby Galaxies.
    There is no optimum solution available, as their 3D x, y, lambda volume far exceeds what can be mapped with present 2D-only detectors. Long-Slit Spectroscopy (LSS) is by far the simplest, most efficient and most used way, but covers only a thin spatial slice at a time. By virtue of its simplicity, it is also still widely used on less than optimum cases. Almost all VLT instruments feature this mode.


  • Extended "Monochromatic" Objects, e.g. Galactic and Extragalactic HII regions, SNRs.
    This is done with Scanning Imaging Spectrographs (S.I.S.). For low spectral resolutions (up to 100) interference filters are generally used. Higher spectral resolutions, up to a few 10,000, are typically the province of the Scanning Fabry-Perot Spectrograph, which covers the whole region in space, but only a thin spectral slice at a shot. Lack of convenient tunable order sorting filters limits its use mainly to kinematic surveys of ionised interstellar matter. At the VLT, it is represented with NACO offering an Adaptive Optics capability.


  • Single "Point" Object, e.g. stars, quasars.
    Their thin, but very long, "beam" shapes along the wavelength axis are perfectly mapped on the 2D detector by the cross dispersed echelle spectrograph (C.D.E.S.). This is the basis for the high resolution optical spectrograph UVES.


  • Multiple "Point" Objects, e.g. star clusters and clusters of galaxies.
    Multi-object spectrographs (MOS), either of the multi-slit or of the multi-fiber flavour, permit efficient surveys of these loose collections of objects. This arguably second most popular mode is well represented on the VLT.


  • Single "Small" Individual Objects, e.g. solar system small bodies, compact HII regions, nuclei of galaxies, galactic cores, interacting galaxies, high-z galaxies
    This recent addition to the instrumental zoo, under the trade name of Integral Field Spectroscopy (IFS), efficiently maps the full 3D astrophysical information on the object (2 spatial, 1 spectral) volume on the detector in one single exposure, provided its size is small, typically 30 x 30 px only. They are based on a classical spectrograph fed by an image slicer, made from a multi-lens, multi-fiber or multi-mirror array. This mode is also well represented at the VLT (fig. 3).


Many VLT Instruments (FORS1+2, ISAAC, NACO, VIMOS, VISIR) are camera spectrographs which, in addition to their spectrographic capabilities, provide direct