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 VLT Survey Telescope (VST) program is a cooperation between the Osservatorio Astronomico di Capodimonte (OAC) and the European Southern Observatory (ESO) that began in 1997. The OAC is one of the institute members of Istituto Nazionale di AstroFisica (INAF), which created a separate institute for the coordination of the whole project, both technological and scientific aspects, named Centro VST a Napoli (VSTceN). VSTcen was founded and directed by Prof. Massimo Capaccioli of the VST project, and hosted at the OAC. The VST was officially approved by the ESO Council in June 1998. After the commissioning phase, handled in collaboration between ESO and VSTceN, ESO will manage the telescope operations and its maintenance. ESO is also responsible for the civil works and the dome on site.
[edit] Description
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. With the 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 hemisphere, 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, composed by a mosaic of 32 2Kx4K CCDs, produced by an international consortium between The Netherlands, Germany, Italy, and the 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.
The telescope will be able to furnish an excellent instrument to the world astronomical community at a 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, as well as 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 successfully tested at the integration site in Italy, 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, the telescope will be shipped and mounted at Cerro Paranal. The first functional tests on site occurred in June 2007, and the entire telescope integration at Paranal was completed at the end of 2007. The first tests with OmegaCAM will occur in the spring of 2008.
