Gravitational eccentric correction optics (GECO): an optical-gravitational device to compensate for flexures in astronomical spectrographs.
Mechanical flexure is a source of major failures in astronomical spectrographs, for which the reimaging of a focal-plane pinhole has to be maintained in position within a fraction of a CCD pixel that has dimensions of the order of 15 microm. The d.o.lo.res. (an acronym for device optimized for low resolution) spectrograph for the Italian national telescope, Galileo, showed displacements of the image of the pinhole more than 10 times greater than expected. The mechanical failure was overcome by the insertion of a passive optical wedge that can add an out-of-phase circle to the flexure ellipse. The results encourage the use of the gravitational eccentric correction optics (GECO) optical-gravitational device in all astronomical observations made with the d.o.lo.res. spectrograph.
Celebrating 20 years of scientific and technical results with the INAF-TNG Telescope
June 9th, 2018 marks the 20th anniversary of the first light of the INAF-Telescopio Nazionale Galileo. This paper is a resume of the main scientific and technical results obtained with the TNG, together with the history of the telescope, the instruments and the people who allowed for several successes and many lessons learned. We will point out what made the TNG a telescope which still can make competitive research in the large and extremely large size telescopes era.
Optical spectroscopy with a near-single-mode fiber-feed and adaptive optics
We report on first astronomical results with a cross-dispersed optical echelle spectrograph fed by a near single-mode fiber. We also present on a novel design of a new adaptive optics (AO) optimized fiber-fed cross-dispersed echelle spectrograph. The spectrograph is designed to match with AO corrected images in the optical bands provided by such as the Mt. Wilson 100 inch, Starfire Optical Range 3.5 m AO telescopes. Ultimately, it will be installed at the 6.5 m MMT, when this has high resolution AO correcting the optical spectrum. The spectrograph, fed by a 10 micron fused silica fiber, is unique in that the entire spectrum from 0.4 micron to 1.0 micron will be almost completely covered at resolution 200,000 in one exposure. The detector is a 2k X 4k AR coated back illuminated CCD with 15 micron pixel size. The close order spacing allowed by the sharp AO image makes the full cover possible. A 250 X 125 mm2 Milton Roy R2 echelle grating with 23.2 grooves mm-1 and a blaze angle of 63.5 deg provides main dispersion. A double pass BK7 prism with 21 deg wedge angle provides cross dispersion, covering the spectrum from order 193 to 77. The spectrograph is used in the quasi- Littrow configuration with an off-axis Maksutov collimator/camera. The fiber feeds the AO corrected beams from the telescope Cassegrain focus to the spectrograph, which is set up on an optical bench. The spectrograph will be used mainly to study line profiles of solar type stars, to explore problems of indirect detection of planets and also study interstellar medium, circumstellar medium and metal abundance and isotopic ratios of extremely metal-poor stars.