VLT Survey Telescope

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VLT Survey Telescope
Organization:	INAF VSTceN - ESO
Location:	Cerro Paranal Observatory, Chile
Altitude:	2600 m
Wavelength:	from UV to I
Built:	in Italy
Diameter:	2.6m
Angular resolution:	0.216 arcsec/pixel
Focal length:	14416 mm
Mounting:	ALT-AZ (Cassegrain)
Website:	[ http://vstportal.oacn.inaf.it ]

The VST (VLT Survey Telescope) program is a cooperation, born in 1997, between the OAC (Osservatorio Astronomico di Capodimonte [ http://www.oacn.inaf.it/ ]) and the ESO (European Southern Observatory [ http://www.eso.org ]). OAC is one of the institute members of INAF (Istituto Nazionale di AstroFisica [ http://www.inaf.it ]), who, since November 2005, created a dedicated Institute devoted to the coordination of the whole project, concerning both technological and scientific aspects, named VSTceN (Centro VST a Napoli [ http://vstportal.oacn.inaf.it/ ]), hosted at the OAC, founded and directed by prof. Massimo Capaccioli, P.I. of the VST project. The realization of the VST is officially regulated by a MoU (Memorandum of Understanding), approved by the ESO Council in June 1998, which foresees the responsibility of the construction and installation on site of the telescope by the INAF - VSTceN. After the commissioning phase, handled in collaboration between ESO and VSTceN, ESO will manage the telescope operations and its maintenance. ESO was also responsible for the civil works and the dome on site.

The VST is an alt-azimutal wide-field survey telescope, with an aperture diameter of 2.6 meters that will be installed in the 2007 at the ESO Cerro Paranal Observatory, in Chile, considered one of the best world-wide astronomical sites, in the same area of the VLT (Very Large Telescope).

With the FOV (Field Of View) of a one square degree, its main scientific role is to furnish a wide-field imaging instrument for the wide exploration of the universe, visible from southern emisphere, able to identify the most suitable targets, to be zoomed by the VLT. At its Cassegrain focus, the VST will host an imaging wide-field camera, named OmegaCAM ([ http://www.astro.rug.nl/~omegacam/ ]), composed by a mosaic of 32 2Kx4K CCDs, produced by an international consortium between Netherland, Germany, Italy and ESO. Together with this focal plane instrument, the VST is able to obtain an high angular resolution (0.216 arcsec/pixel), and it will be capable to perform stand alone observations in the wide spectral range between UV and I.

Used in combination with the VLT, the VST will be able to furnish an excellent instrument to the world astronomical community in order to reach the frontiers of knowledge in ground-based astrophysics at an high spatial resolution. For this purpose, since first design phases, the telescope was object of a careful investigation of all its components, in order to produce very stable images.

A very careful design has been devoted to the solutions adopted in the active optics system, implemented and actually under optimization on the telescope. The thin primary mirror is provided with an actuator network (84 axial distributed under the mirror surface and 24 radial dislocated laterally) able to locally correct the optical surface, while the secondary mirror is activelly controlled by a double deformable platform (hexapod) able to tilt the mirror during exposure, maintaining stable its optical performances and correcting all deformation effects induced by thermal gradient and by the gravitational components on the opto-mechanical structure. The active optics system is also provided with a wave front sensor (Shack-Hartmann), mounted under the primary mirror cell together with local guide system, able to furnish the optical correction feedback. These systems gives the capability to the VST to be autonomous in terms of guide and active optics control. It is also foreseen an external guide and wave-front sensor device, provided internally by the focal plane instrument.

The tracking system, involving main axes (AZ, Azimuth provided with a hydrostatic bearing system, ALT, Altitude and ROT, field rotator) is able to guarantee a positioning and tracking precision with a maximum error of 0.05 arcsec R.M.S. and it was already succesfully tested at the integration site in Italy (Mecsud, Scafati, Napoli), where the INAF staff has conducted all mounting and testing phases for all mechanical, electronic, electrical and control software components.

In the primary mirror cell it is installed an instrument able to modify the telescope optical configuration, moving from a corrector composed by a double set of lenses, to an ADC (Atmospherical Dispersion Corrector) composed by a counter-rotating couple of prisms, potentially able to correct the optical dispersion phenomena, due to the variation of air mass induced by the changing ALT angle.

After dismounting, painting and packing phases, actually under development, the telescope will be shipped and mounted at Cerro Paranal. First sub-assembly parts (Azimuth system) shipping is foreseen in April 2007 and their first functional tests on site are foreseen in June 2007. The whole telescope integration at Paranal is foreseen in the end of 2007. First light with omegaCAM is foreseen in the spring of 2008.

For further information about the project, it is possible to visit the VST official web site:

[ http://vstportal.oacn.inaf.it/ ]

M. Brescia, Public Outreach Department - VSTceN