Contributors: C. Baffa, V. Biliotti, G. Comoretto, V. Gavryusev, S. Gennari, F. Lisi, E. Oliva., A. Richichi
The group involved in the area of instrumentation for near infrared
bands gave the traditional support to the TIRGO observatory, making
operative the instruments offered to guest observers ARNICA, LonGSp,
and the IR photometer [], [], [],
supporting external groups when observing with their own
instrumentation, and covering the needs of the telescope itself. During
1996, the new control software (named xnir) has been officially
released []. It allows full control and data acquisition for
the TIRGO instrumentation based on array detectors []. The
camera ARNICA was equipped with a new observing mode, which allows fast
photometry on a portion of the array detector. It is possible to record
or 
pixel images with a sampling time as
low as 7 ms. This makes viable to observe lunar occultation events with
ARNICA, obtaining more sensitivity [] than with single
detector photometers, and also to help studying the temporal variations
of the atmospheric turbulence in the infrared bands, so giving a very
useful tool to the designers of adaptive optics systems. As a further
add-on for ARNICA, we studied the feasibility of the low-resolution
spectroscopic mode ( 
) based on a set
of grisms inserted at the focal plane of the TIRGO optics.
A great effort was spent porting the IR camera ARNICA to two different telescopes, the NOT (Nordic Optical telescope) on Canary Islands and the VATT(Vatican Advanced Technology Telescope) on Mt. Graham (Arizona), with a long round trip which started on July and was completed on January 1997. This was the second time of ARNICA at NOT [], after the observations performed on summer 1995. The VATT observations required the design of a new optical system to match the excellent optical quality of the telescope, a new mechanical interface, and a new software for communications to and from the telescope; in particular, the advanced telescope control system of VATT required the use of the package xnir for controlling ARNICA, so giving it a demanding test on the field for the first time. The observing run was conducted in collaboration with the VATT staff, on behalf of Italian astronomers and Steward Observatory researchers, and demonstrated for the first time the very good quality of infrared data taken on Mt. Graham, the future site of the Large Binocular Telescope.
The NICS project, aimed to equip the focal plane of the TNG with a high
quality instrument for photometry and spectroscopy in the near infrared
bands, produced a prototype of the control electronics, that has been
tested and used to begin software development ([],
[]); the NICS software at the laboratory test level is
largely based on the package xnir, produced for the TIRGO
instrumentation. The final details of the optical system were defined.
To assess the feasibility of polarimetric observations, the optical
characteristics of birefringent crystals transmitting in the near
infrared (0.9-2.5 
m) were analyzed in much details. LiYF 
and
AgGaS 
were identified as the best materials for manufacturing IR
Wollaston prisms while new measurements of the IR transmission of
Calcite (CaCO 
) showed that this material is not suitable for IR
applications []. New concepts for polarizing beam
splitters were also investigated and a simple system which allows
simultaneous measurements of the polarized flux at 0, 45, 90 and 135
degrees (i.e. a single shot definition of the first 3 Stokes'
parameters) was developed [].
Contributors: R. Barletti, G. Comoretto, G.P. Curioni, P. Curioni, M. Massi, D. Panella, G. Tofani
The main activity of the radioastronomical group has been the development of new hardware and software with special reference to the use of the two radiotelescopes of the Istituto di Radioastronomia in Bologna (Medicina and Noto). In particular the following developments have been caried out:
Two copies of the ARCOS autocorrelation spectrometer have been completed. The first is operative since August at the Noto radiotelescope []. The second will be operative from February 1997 at the Medicina radiotelescope.
A new version of the control software for these instruments, based on the object programming technique, is under development.
These instruments are used in several observative projects on water vapor emission from star forming regions and late type stars {[], []).
The 43GHz receiver has been upgrated with the installation of a cold polarizer. It has been tested during two runs of 10 days each at the Noto radiotelescope. During these tests the receiver was used in July for a run of spectroscopy observations of the SiO masers [] and in September for a VLBI run on the SiO line []. These tests were a basic opportunity to evaluate the Noto antenna at its performance limit.
A technique for measuring the surface quality of a reflector as been used on the Medicina radiotelescope. The technique uses amplitude measurements of the far field, and a fitting algorithm developed at the University of Napoli to retrieve the phase of the radio wavefront []. This technique has been applied to monitor the deformations in the Noto radiotelescope [].
Within a program aimed to upgrade Medicina and Noto radiotelescopes, a study of the electromagnetic performance of the antenna system has been caried out. A research on the scattering effects of the panel discontinuities has been performed using FEM analysis []. Numerical methods of analysis on electromagnetic structures have been applied to the problem of high purity waveguide polarizers [].
A Doppler analyzer is currently being built. This instrument will be used for radio science experiments with the Cassini interplanetary probe [].
The need for instrumentation operating in the mm-submm range, in the perspective of projects such as FIRST, COBRAS, LSA, has oriented the group toward the development of new technologies for receivers and spectral analysis.
The 330-350GHz receiver, a cooperation with the Rutheford Appleton Laboratory (UK), has been upgraded with a Schottky diode mixer with lower noise temperature and a more powerfull multiplier.
A cooperation with Galileo Ferraris Institute and the Universities of Milano and Torino, has produced interesting results in the field of the development of SIS receivers [].
The feasibility study for a new radiotelescope (SRT: Sardinia RadioTelescope) with active surface has been completed. The results have been presented at the workshop on new antenna technologies held in ESTEC [].
Theoretical work on VLBI data reduction has been completed, investigating the possibilities of correcting closure terms due to polarization impurities [].
Contributors: C. Baffa, G. Brusa, S. di Serego Alighieri, L. Fini, S. Gennari, F. Lisi, E. Oliva, P. Ranfagni
In Arcetri the activities for the Galileo National Telescope (TNG), whose Project Office is at the Padova Observatory, have concentrated on the development of the Near Infrared Camera and Spectrograph (NICS), described in the section on ``Infrared Instrumentation'' and of the TNG Adaptive optics Module, described in the section on ``Adaptive Optics Systems for Large Telescopes'', on the scientific and technical support to the development of the Low Dispersion Spectrograph (LDS) and to the definition and design of the TNG Archives, and on the praparations for the operational phase of the TNG to start in 1997 []. An operation base office has been set up in Santa Cruz de La Palma in collaboration with the british/dutch ING group and the nordic NOT group. A detailed plan for the operations of the TNG observatory on La Palma and for the necessary personnel has been prepared. Active participation to the ruling bodies of the Observatorio del Roque de los Muchachos on La Palma has continued.
Contributors: F. Cavallini, G. Ceppatelli, F. Fabiani, G. Falcini, T. Grisendi, S. Paloschi
The renovation of the electric and control systems of the Solar Tower telescope and spectrograph has been completed in 1996 with the re-building of the automatic guiding system. This system has been duplicated and it is disposable now either on the Solar Tower or on the UBF laboratory.
The construction of the Italian Panoramic Monochromator (IPM) has been completed in the summer 96, and in September the instrument has been installed at the THEMIS solar telescope in Tenerife (Canary Islands).
This instrument basically consists of a
piezo-scanned, capacity servo-controlled, Fabry-Perot
interferometer (Queensgate Mod. ET-50), used in telecentric
mounting, in series with an Universal Birefringent Filter,
used as order sorter. It has been designed to
obtain monochromatic images of the solar surface, in the
wavelength region between 4600 and 6800 Å, with high
spatial ( 
0.2") and spectral resolution
( 
/ 
= 256,000), on a sqare field
34" 
34".
The instrumental profile (essentially one order of the
interferometer) is symmetrical and very stable in
wavelength, showing a typical drift of 20 ms 
over a period of a day. Anyhow, a wavelength control, which
uses the 6438 Å line of a Cd 
lamp (secondary
wavelength standard), allows to measure the residual drift
with a precision of about 
5 ms (the
wavelength stability of the Cd line).
The same spectral lamp can be also used to measure the
spectral dishomogeneities on the final focal plane
( 350 ms ), produced by flatness
errors of the interferometer plates ( /150 after
coating), with a precision of 10 ms .
Two CCD cameras (512 512 square pixels, 19 m in
size), developed at Rome II University, are used as
detectors and allow simultaneous imaging in monochromatic
and white light, for reference and destretching
procedures.
The control software (built in C language under HPUX-10.1 with X11, Motif1.2 and HP-SICL libraries) allows the complete control of the instrument using an HP745 Workstation, connected to the acquisition system (two PC's and CCD cameras) and to the main computer of the THEMIS telescope. The user's interface is a window with a menu bar to interactively choose the appropriate sequence of operations on the instrument.
The first half of 1996 has been devoted to complete the IPM and to perform many tests to verify the correct behaviour of the control software and of the mechanical, optical and electronic parts. In July the instrument has been disassembled and then shipped to Tenerife, where, in the period August 26 - October 5, it has been installed at THEMIS. The telescope, however, was not yet operative in that period (the optics was not correctly aligned, the tube was not evacuated and the seal between the tube and the dome was not yet installed). For these reasons the spatial resolution was very poor and no detail of the solar surface was visible. However, three spectral series were taken on the profile of the 5576 Å Fe I line, putting an optical target on the telescope focal plane. The images so obtained have confirmed the correctness of the optical and spectral instrumental behaviour. The IPM is operative now, and as from April 10, 1997 it will be at observers disposal.
Contributors: C. Del Vecchio, L. Fini, L. Miglietta, D. Puccetti, P. Salinari.
The Large Binocular Telescope Project (formerly Columbus Project ) is a collaboration between Italy, where Arcetri is the centre of activity, the University of Arizona and the Research Corporation to build the largest telescope presently planned for the Northern Hemisphere. At the end of 1996 two new partners, Ohio State University and a consortium of German Institutes (LBTB), started formal negotiations to acquire 12.5 % each of the project partnership.
The telescope will be equipped with two large primary mirrors (8.4 m diameter) and is designed to achieve top class performances in a variety of observing modes at near-ultraviolet, visible, and infrared wavelengths. The observing modes include diffraction limited imaging (single pupil and interferometric, providing up to 23 m maximum base line), wide field imaging multi-object spectroscopy (one degree field), high resolution spectroscopy.
During 1996 the optimisation of the main telescope structure and the final design of all telescope components was completed. At the end of the year the technical documentation for the call for tender was in preparation and the call for tender for all the main telescope components was planned for the spring 1997.
In late spring 1996 construction work, that had been stopped by a legal action during 1995, could be resumed on Mt. Graham. Before the winter season LBT site clearing was completed, the access road constructed, the ground escavated and the concrete foundation of the telescope pier was successfully poured.
The preparation of the furnace and of the mold for casting the first of the two 8.4 m diameter honeycomb mirrors was also completed within 1996. The casting took place in January 1997.
In summary 1996 was a very important year for the LBT project,that entered the construction phase with the perspective of completing the telescope and instrumentation as originally planned in 1989, thanks to the likely acquisition of new partners replacing those lost after 1989.
Contributors: V. Biliotti, G. Brusa, C. Del Vecchio, S. Esposito, L. Fini, P. Ranfagni, A. Riccardi, P. Salinari, P. Stefanini
The scope of adaptive correction of the blur induced by atmospheric turbulence is to sharpen the astronomical images to the limit posed by diffraction, therefore achieving higher angular resolution and, at the same time, higher sensitivity. The gain is potentially larger for larger telescopes, but also the system complexity increases dramatically.
Two adaptive optics systems have been developed in parallel by the Arcetri group in the last few years: the TNG Adaptive Optics Module, in collaboration with the Observatory of Padova, and the Adaptive Secondary Project, in collaboration with Politecnico di Milano and Steward Observatory. The first one will provide low order correction in the near infrared soon after first light of the Galileo telescope, while the second is aimed at developing a much more ambitious system for high order correction, to be used in its initial version on the 6.5 m MMT -Conversion and, on a longer time scale, by LBT and Galileo.
The Arcetri AO group completed the development of the "tip-tilt" correction unit and of the associated sensor, based on Avalanche Photo Dyodes, and delivered the components to the Padua Observatory in mid 1996. The integration in the Adaptive Optics Modulus of the Galileo Telescope continued there in 1996 and will be followed by full system test and then by installation on the telescope in 1997.
During 1996 the design of all the components and of the entire system for the MMT adaptive secondary unit was defined, and a prototype system including all the components and all the functions was designed in detail and contracted out for construction. The prototype consists of the first two rings of actuators (30 in total, versus 390 in ten rings for the final MMT unit) mounted in an identical geometry as the final unit and uses identical analogic and digital electronics cards. It will therefore be used for development of control algorithms, for system debugging (hardware and software) and for realistic performance evaluation. Most components have been delivered at the end of 1996 and full system integration and test is foreseen for spring 1997.
The adaptive optics group was also active in a variety of other fields, in particular in analytical and numerical simulations of adaptive systems, in the development of a new technique to obtain tip-tilt information from laser beacons and in the development of a new wave front sensor based on the classical Foucault test. Geometrical and Fourier optics study and numerical simulation of this new wavefront sensor show very promising features, that received a preliminary confirmation at the end of 1996 by a simple laboratory test []. Further development of the new device is foreseen in 1997.