Transmission curves and theoretical calculi of the magneto-optical filter, designed and built by the authors, are shown together with some observed transmission spectra. At present the filter has a total halfwidth of ~ 80 m/~; and the maximum transmission is 25 ~. From the analysis of the theoretical curves and from the observed spectra, we deduced the possibility of making up a filter with a very narrow passband (less than 30 rr~) and a very high transmission (up to nearly 100% apart from losses arising from the glass cell, lenses and polarizers).The article concludes with a selection and discussion of photographs obtaine, d with the filter.* Present address: Osservatorio Astrofisico di Arcetri, Firenze, where the whole of this research has been carried out. Solar Physics 44 (1975) 509-518. AH Rights Reserved Copyright 9 1975 by D. Reidel Publiahing Company, Dordrecht-Holland
In this paper we describe the solutions adopted for the design and the realization of an astronomical CCD imaging system, the results achieved on a Schmidt telescope (l°xl° Field Of View, FOV) and, as well, the images obtained on a 30 cm prototype of a really innovative wide field telescope (2°x20 FOV), a twomirrors Three-Reflection Telescope (TRT), adopting aspherical reflecting-only surfaces. This solution allows the correction of every aberration, removing completely the vignetting and the field-curvature on very large fields of view (FOV). The CCD camera (equipped with a Loral 2kx2k chip), operating under "inverted mode" (Multi-Phase-Pinned mode, MPP), shows a dark current less than 0.1 e7min at a temperature of only 200°K. This particular operational mode enables the camera to provide accurate photometry even when the CCD is not at "conventional" cryogenic temperatures. To cool-down the CCD chip it has been designed and realized a sophisticated Thermo-Electric-Cooler (ThC), which uses a three-stage Peltier module and glycol circulating in closed circuit at minus 10°C as heat exchanger. This TEC can reach, in this arrangement, an operative temperature of minus 80°C, approaching the typical performance ofusual cryogenic systems. For its small encumber and for its reliability it is especially suitable for applications in which the room available is small, such as in internal-focus telescopes (e.g. Schmidt telescopes). Finally we briefly report new CCD and telescope projects.The recent rapid development of large size telescopes (Li') has stimulated new and important researches in all fields of Astrophysics, and a large amount of new and fundamental results are coming out, such as the discovery of circumstellar rings around nearby stars, the detailed structure of the star forming regions, the late stages of stellar evolution, up to the large scale faint galaxy distribution. The beginning of the next millennium will be characterized by the many large telescopes in operation such as GEMINI, VLT, BLT and the KECK twin-telescopes working already. But not all future astronomical researches will be done with large telescopes. Most ofthe fundamental science will require telescopes ofthe 1-4 m class operating side by side to the LTs. Actually, one main constraint of the new technology telescopes is that they essentially are pointed observatories which are investigañng a single object or a small field of the sky. But there are many fundamental astrophysical problems which can be tackled only by systematic sky surveys with intermediate-size, large field telescopes, which should be considered as a necessary complement to the LTs. These astrophysical problems include many issues of lively interest such as the search of minor bodies of the Solar System, the astroseismology and stellar activity, the hidden matter, the local low mass stellar population, the frequency of binary and multiple stellar systems, the rate of cataclysmic events in the Milky Way and in nearby galaxies, the frequency of supernova explosions in distant ga...
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