Fabio Bortoletto

Final commissioning phase of the AdOpt@TNG module

The AdOptTNG module is an adaptive optics facility permanently mounted at the Nasmyth focus of the 4m-class Telescopio Nazionale Galileo (TNG). Its integration on the telescope started in late November 1998 and first-light of the speckle and tip-tilt modes took place shortly after. Both modes have been offered to the astronomical community and turned out to provide performances close to the expectations. Double stars with separation below 0.1 arcsec have been resolved by the speckle facility. Improvement of the Strehl ratio of a factor two and enhancement in the FWHM from 0.65 arcsec to 0.35 arcsec have been obtained on relatively faint reference stars. The high-speed low noise CCD, namely an 80 X 80 pixel read from the four corners, has been mounted and aligned with the Shack-Hartmann wavefront sensor. A Xinetics mirror with 96 actuators has been calibrated against the wavefront sensor with on-board alignment fibers. This has been done using a modal approach and using Singular Value Decomposition in order to get a reliable interaction matrix. Filtering can be modal too, using a default integrative filter coupled with a limited FIR-fashioned technique. Open loop measurements on the sky provide data to establish open loop transfer functions and realistic estimates of limiting magnitude. High-order wavefront correction loop has been successfully tested on the sky. In this paper we give a description of the overall functionality of the module and of the procedure required to acquire targets to be used as reference in the correction. A brief overview of the very first astronomical results obtained so far on angular size and shape measurements of a few asteroids and sub-arcsec imaging of Planetary Nebulae and Herbig Haro objects is also given.

NGST MIRI instrument

The MIRI is the mid-IR (5-28μm) instrument for NGST and provides for imaging, cororographic, high- and low-resolution spectroscopic capabilities. Unlike to the other instruments on NGST, the MIRI must be cooled - to reduce the thermal background from the optics and because the detectors require an operating temperature of about 7k.. In this paper we summarise the science goals, the proposed overall opto-mechanical concept, the thermal design aspects, the detectors and the expected sensitivity of the instrument.

CCD cameras for the Italian national telescope Galileo

In the last years, the Charge Coupled Device (CCD) detectors have had a great development: 2048 X 2048 pixel formats are routinely produced by silicon foundries with good electro- optical characteristics. Scientific CCDs now, not only offer the ability to be read from more than one output, but they can also be buttable to form mosaics in order to cover a larger field of view, requirement posed by the current telescope technology. The Italian National Telescope GALILEO (TNG) will support a large set of visual and near IR detectors dedicated to scientific measurements at the focal plane. Also tracking systems and Shack-Hartmann wavefront analyzers will be based on CCD technology. Due to the number of camera systems to be routinely operated, the possibility to have uniformed interaction and configuration of systems is emerged as an important requirement for this crucial part of the telescope. In this paper the detector and instrument plan foreseen for the TNG telescope will be presented on the first part, while on the second we will present the CCD controller, now at the end of development. Here presented is a modular system based on digital signal processors and transputer modules. It is interfaced to host computers (PCs, workstations or VME crates) via optical fibers and a specially developed VME-VSB interface board.

Active optics handling inside Galileo Telescope

A large part of the active optics system and control environment for the Galileo telescope has been developed and tested. Presently the primary mirror support cell has been characterized for the mechanical and optical aspects. The primary mirror has also been characterized and tested with the active support system in work. Part of the mechanics for the secondary and tertiary active mirror supports has been constructed and we plan to start the characterization work in the second half of this year. An overview of the main results obtained during factory acceptance tests and a discussion about the general informatics implementation is here provided.

Commissioning of the Italian National Telescope Galileo

The commissioning phase of the Telescopio Nazionale Galileo is started during the first half of 97. Large parts of the drive, the optical and the control system have been mounted at the telescope in site (LaPalma, Canary Islands). The telescope is expected to be ready for the technical first- light during February - March 98 while the instrumentation first-light is expected for mid 98. On this review of the commissioning operations we will describe the problems encountered and the results achieved integrating the main telescope subsystems.

Photochromic polymers for erasable focal plane masks and rewritable volume-phase holographic gratings

Thermally irreversible photochromic materials, mainly belonging to the diarylethene class, are potentially useful as optoelectronic devices. Poly-1,2-bis-(2-methyl thiophen-3-yl)perfluorocyclopentene has been studied in order to verify its possible application in astronomy for the production of re-writable focal plane masks and volume phase holographic gratings. Films of photochromic materials embedded in an amorphous polymer matrix are obtained by casting from chloroform solution. The films show a good transparency in the visible region when the photochromic molecule is in the open-ring form, while they totally absorb visible wavelength radiations when the photochrome is in the other isomeric form. The variation in refractive index between the two photochromic isomers, evaluated by UV-vis-NIR absorption spectra, is large enough to make this photochromic apt for the production of volume phase holographic gratings.

Status of the Galileo National Telescope

The Project Telescopio Nazionale GALILEO (TNG) will provide a 3.5-m telescope for the Italian astronomical community. Its main features closely parallel those of the ESO New Technology Telescope (NNT). We describe here its characteristics and its most important differences with respect to the NTT. The figuring of the three mirrors was successfully completed, with results exceeding the specifications. The telescope structure has been assembled in the workshop, and alignment tests are under way. The control system (motors, encoders, VME and workstation environment) is also in an advanced stage of development. The TNG will be part of the Observatorio del Roque de los Muchachos, in the Canary Islands. Its location is on the West side of the mountain, some 400-m from the NOT; excavation works are already well advanced. Civil works should be finished in the course of the current year. It is expected to complete the rotating building, and the erection of the telescope before the end of 1995, to start regular operations in 1996.

The New Generation CCD Controller: First Results

The new generation CCD controller, developed by the Italian Detector Working Group (DWG), is an improvement on the CCD controller in use at TNG. A new interface with the host computer, based on a high-speed link and PCI board, able to sustain high data transfer rate has been designed and built. The sequencer has been modified in order to improve high-speed clocks and different reading modes. A new analogue board based on a fast ADC’s and new signal processing has been designed. The board is able to process four channels simultaneously allowing high acquisition rates. Preliminary tests demonstrating the improved performances of the controller are shown.

Rewritable photochromic focal plane masks

The application of organic photochromic materials in astronomy is opening new possibilities which we are investigating in order to design innovative devices for future instrumentation. The photochromic property of transparent/opaque transition (although in a limited wavelength range) and the changes in intrinsic refractive index have led our studies to application in astronomic spectrographs, both as focal plane mask (for MOS application) and as dispersive elements (volume phase holographic gratings, VPHG), respectively. In both cases the possibility to write and erase devices with suitable irradiation has revealed a new perspective for non-disposable and fully customizable items for spectroscopy. Pursuing this goal we have synthesized a series of novel photochromic materials belonging to the diarylethenes. They fulfill the requirements of thermal stability and fatigue resistance necessary to build functional devices. Prototypes of high contrast focal plane mask working in the H-alpha spectral region have been manufactured and characterized both in laboratory and with the AFOSC camera at Asiago telescope (1.8 m). A custom writing robot (ARATRO) which, taking imaging frames and with the aid of interactive mask design software and ad hoc control electronics, is able to write MOS masks, has been constructed. The design of the MOS masks allow the fitting in the AFOSC slit wheel. The overall set-up is ready for the sky tests.

Moving M2 mirror without pointing offset

High precision movement of telescope mirrors in two-mirror telescopes is examined. Active optics are used for high precision movement of M2 during exposures to introduce a specific amount of decentering coma. It is shown that the decentering coma may be controlled by high accuracy rotation of the mirror around a point near the center of curvature of M2. Basic equations are developed for the displacement of the barycenter of the geometric blur. A relation is obtained for determining the correct position around which the rotation should be performed. The application of these techniques to two-mirror telescopes is discussed. Ray tracing and analytical results were compared and showed good agreement.