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And Then There Were Three...!

VLT MELIPAL Achieves Successful "First Light" in Record Time

28 Gennaio 2000

This was a night to remember at the ESO Paranal Observatory! For the first time, three 8.2-metre Very Large Telescopes (VLTs) were observing in parallel, with a combined mirror surface of nearly 160 metres squared. In the evening of January 26, the third 8.2-metre Unit Telescope, MELIPAL ("The Southern Cross" in the Mapuche language), was pointed to the sky for the first time and successfully achieved "First Light". During this night, a number of astronomical exposures were made that served to evaluate provisionally the performance of the new telescope. The ESO staff expressed great satisfaction with MELIPAL and there were broad smiles all over the mountain.

The first images

Following two days of preliminary adjustments after the installation of the secondary mirror, cf. ESO Press Photos eso0003, MELIPAL was pointed to the sky above Paranal for the first time, soon after sunset in the evening of January 26. The light of a bright star was directed towards the Guide Probe camera, and the VLT Commissioning Team, headed by Dr. Jason Spyromilio, initiated the active optics procedure. This adjusts the 150 computer-controlled supports under the main 8.2-metre Zerodur mirror as well as the position of the secondary 1.1-metre Beryllium mirror. After just a few iterations, the optical quality of the recorded stellar image was measured as 0.46 arcsec (ESO Press Photo eso0004), a truly excellent value, especially at this stage!

Immediately thereafter, at 22:16 hrs local time (i.e., at 01:16 hrs UT on January 27), the shutter of the VLT Test Camera at the Cassegrain focus was opened. A 1-min exposure was made through a R(ed) optical filter of a distant star cluster in the constellation Eridanus (the River). The light from its faint stars was recorded by the CCD at the focal plane and the resulting frame was read into the computer.

Despite the comparatively short exposure time, myriads of stars were seen when this "first frame" was displayed on the computer screen. Moreover, the sizes of these images were found to be virtually identical to the 0.6 arcsec seeing measured simultaneously with a monitor telescope, outside the telescope enclosure. This confirmed that MELIPAL was in very good shape. Nevertheless, these very first images were still slightly elongated and further optical adjustments and tests were therefore made to eliminate this unwanted effect. It is a tribute to the extensive experience and fine skills of the ESO staff that within only 1 hour, a 30 sec exposure of the central region of the Crab Nebula in Taurus with round images was obtained, cf. ESO Press Photo eso0004.

The ESO Director General, Dr. Catherine Cesarsky, who assumed her function in September 1999, was present in the Control Room during these operations. She expressed great satisfaction with the excellent result and warmly congratulated the ESO staff to this achievement.

She was particularly impressed with the apparent ease with which a completely new telescope of this size could be adjusted in such a short time. A part of her statement on this occasion was recorded on ESO Press Video eso0002 that accompanies this Press Release.

Three telescopes now in operation at Paranal

At 02:30 UT on January 27, 2000, three VLT Unit Telescopes were observing in parallel, with measured seeing values of 0.6 arcsec (ANTU - "The Sun"), 0.7 arcsec (KUEYEN -"The Moon") and 0.7 arcsec (MELIPAL).

MELIPAL has now joined ANTU and KUEYEN that had "First Light" in May 1998 and March 1999, respectively. The fourth VLT Unit Telescope, YEPUN ("Sirius") will become operational later this year.

While normal scientific observations continue with ANTU, the UVES and FORS2 astronomical instruments are now being commissioned at KUEYEN, before this telescope will be handed over to the astronomers on April 1, 2000.

The telescope commissioning period will now start for MELIPAL, after which its first instrument, VIMOS will be installed later this year.

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