This is the first facility of its type ever installed on an 8-m class telescope, now providing exceptional observing capabilities for the imaging and spectroscopic studies of very complex sky regions, e.g. stellar nurseries and black-hole environments, also in distant galaxies.

Following smooth assembly at the 8.2-m VLT Yepun telescope of SINFONI's two parts, the Adaptive Optics Module that feeds the SPIFFI spectrograph, the "First Light" spectrum of a bright star was recorded with SINFONI in the early evening of July 9, 2004.

The following thirteen nights served to evaluate the performance of the new instrument and to explore its capabilities by test observations on a selection of exciting astronomical targets. They included the Galactic Centre region, already imaged with the NACO AO-instrument on the same telescope.

Unprecedented high-angular resolution spectra and images were obtained of stars in the immediate vicinity of the massive central black hole. During the night of July 15 - 16, SINFONI recorded a flare from this black hole in great detail.

Other interesting objects observed during this period include galaxies with active nuclei (e.g., the Circinus Galaxy and NGC 7469), a merging galaxy system (NGC 6240) and a young starforming galaxy pair at redshift 2 (BX 404/405).

These first results were greeted with enthusiasm by the team of astronomers and engineers [2] from the consortium of German and Dutch Institutes and ESO who have worked on the development of SINFONI for nearly 7 years.

The work on SINFONI at Paranal included successful commissioning in June 2004 of the Adaptive Optics Module built by ESO, during which exceptional test images were obtained of the main-belt asteroid (22) Kalliope and its moon.

Moreover, the ability was demonstrated to correct the atmospheric turbulence by means of even very faint "guide" objects (magnitude 17.5), crucial for the observation of astronomical objects in many parts of the sky.

SINFONI: A powerful and complex instrument

A new and very powerful astronomical instrument, a world-leader in its field, has been installed on the Very Large Telescope at the Paranal Observatory (Chile).

Known as SINFONI ("Spectrograph for INtegral Field Observation in the Near-Infrared"), it was mounted in two steps at the Cassegrain focus of the 8.2-m VLT YEPUN telescope.

First Light of the completed instrument was achieved on July 9, 2004 and various test observations during the subsequent commissioning phase were carried out with great success.

SINFONI has two parts, the Near Infrared Integral Field Spectrograph, also known as SPIFFI (SPectrometer for Infrared Faint Field Imaging), and the Adaptive Optics Module.

SPIFFI was developed at the Max Planck Institute for Extraterrestrische Physik (MPE) (Garching, Germany), in a collaboration with the Nederlandse Onderzoekschool Voor Astronomie (NOVA) in Leiden, the Netherlands Foundation for Research in Astronomy (ASTRON) (The Netherlands), and the European Southern Observatory (ESO) (Garching, Germany).

The Adaptive Optics (AO) Module was developed by ESO.

Once fully commissioned, SINFONI will provide adaptive-optics assisted Integral Field Spectroscopy in the near-infrared 1.1 - 2.45 �m waveband.

This advanced technique provides simultaneous spectra of numerous adjacent regions in a small sky field, e.g., of an interstellar nebula, the stars in a dense stellar cluster or a galaxy.

Astronomers refer to these data as "3D-spectra" or "data cubes" (i.e., one spectrum for each small area in the two-dimensional sky field), cf. Appendix A.

The SINFONI Adaptive Optics Module is based on a 60-element curvature system, similar to the Multi Application Curvature Adaptive Optics devices (MACAO), developed by the ESO Adaptive Optics Department and of which three have already been installed at the VLT (ESO PR 11/03); the last one in August 2004.

Provided a sufficiently bright reference source ("guide star") is available within 60 arcsec of the observed field, the SINFONI AO module will ultimately offer diffraction-limited images (resolution 0.050 arcsec) at a wavelength of 2 �m.

At the centre of the field, partial correction can be performed with guide stars as faint as magnitude 17.5. In about 6-months' time, it will benefit from a sodium Laser Guide Star, achieving a much better sky coverage than what is now possible.

SPIFFI is a fully cryogenic near-infrared integral field spectrograph allowing observers to obtain simultaneously spectra of 2048 pixels within a 64 x 32 pixel field-of-view.

In conjunction with the AO Module, it performs spectroscopy with slit-width sampling at the diffraction limit of an 8-m class telescope.

For observations of very faint, extended celestial objects, the spatial resolution can be degraded so that both sensitivity and field-of-view are increased.

SPIFFI works in the near-infrared wavelength range (1.1 - 2.45 �m) with a moderate spectral resolving power (R = 1500 to 4500). More information about the way SPIFFI functions will be found in Appendix A.

"First Light with SINFONI's Adaptive Optics Module

Because of the complexity of SINFONI, with its two modules, it was decided to perform the installation on the 8.2-m VLT Yepun telescope in two steps.

The Adaptive Optics module was completely dismounted at ESO-Garching (Germany) and the corresponding 6 tons of equipment was air-freighted from Frankfurt to Santiago de Chile. The subsequent transport by road arrived at the Paranal Observatory on April 21, 2004.

After 6 weeks of reintegration and testing in the Integration Hall, the AO Module was mounted on Yepun on May 30 - 31, together with a high-angular-resolution near-infrared Test Camera.

Technical "First-Light" with this system was achieved around midnight on May 31st by observing a 11-magnitude star, reaching right away the theoretical diffraction limit of the 8.2-m telescope (0.06 arcsec) at this wavelength (2.2 �m).

Following this early success, the ESO AO team continued the full on-sky tuning and testing of the AO Module until June 8, setting in particular a new world record by reaching a limiting guide-star magnitude of 17.5, two-and-a-half magnitudes (a factor of 10) fainter than ever achieved with any telescope!

The ability to perform AO corrections on very faint guide objects is essential for SINFONI in order to observe very faint extragalactic objects.

During this commissioning period, test observations were performed of the binary asteroid (22) Kalliope and its moon Linus. They were made by the ESO AO team and served to demonstrate the high performance of this ESO-built Adaptive Optics (AO) system at near-infrared wavelengths.

"First Light" with SINFONI

The fully integrated SPIFFI module was air-freighted from Frankfurt to Santiago de Chile and arrived at Paranal on June 5, 2004.

The subsequent cool-down to -195 �C was done and an extensive test programme was carried through during the next two weeks. Meanwhile, the AO Module was removed from the telescope and the "wedding" with SPIFFI was celebrated on June 20 in the Paranal Integration Hall.

All went well and the first AO-corrected test spectra were obtained immediately thereafter. The extensive tests of SINFONI continued at this site until July 7, 2004, when the instrument was declared fit for work at the telescope.

The installation at the 8.2-m VLT Yepun telescope was then accomplished on July 8 - 9.

"First Light" was achieved in the early evening of July 9, 2004, only 30 min after the telescope enclosure was opened.

At 19:30 local time, SINFONI recorded the first AO-corrected "data cube" with spectra of HD 130163. This 7th-magnitude star was observed in the near-infrared H-band with a moderate seeing of 0.8 arcsec.

Test Observations with SINFONI

Until July 22, test observations on a number of celestial objects were performed in order to tune the instrument, to evaluate the performance and to demonstrate its astronomical capabilities.

In particular, spectra were obtained of various highly interesting celestial objects and sky regions:

images and spectra of the young starforming galaxies BX 404/405, casting more light on the formation of disks in spiral galaxies (Appendix G)

The SINFONI Teams

The first SINFONI results have been greeted with enthusiasm, in particular by the team of astronomers and engineers from the consortium of German and Dutch institutes and ESO who worked on the development of SINFONI for nearly 7 years.

Some of the members of the Commissioning Teams are depicted in PR Photos 24g/04 and 24h/04; in addition to the SPIFFI team members present on the second photo, Walter Bornemann, Reinhard Genzel, Hans Gemperlein, Stefan Huber have also been working on the reintegration/commissioning in Paranal.

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