There are many ways to achieve the positioning accuracy established from tolerance in a cryogenic environment. One method is an opto-mechanical design which stays aligned at room temperature and at liquid nitrogen temperature without modifications. This could be achieved using aluminium mirrors with thermally matched aluminium holders and optical bench, that isotropically contract at cryogenic temperatures.
The design of holders should allow some adjustment of the optics positions to correct possible errors in the manufacturing of the optical bench and/or optical holders themselves, without precluding the isotropic contraction during the cooling to the working temperature.
This work illustrates the last prototype of cryogenic mirror-holder developed in our laboratory. The mirror mounting is based on a set of six forces which pull the mirror against the tree orthogonal faces of a reference corner. Adjustments to the mirror alignment can be achieved by means of six aluminium micrometers. Here we describe the device and illustrate the test results.
GIANO is a cryogenic cross-dispersed spectrometer whose optics consist of aspheric aluminum mirrors, glass flats, cross-dispersing prisms and a grating fixed onto a ~1.5×1.0 m aluminum bench. The primary aim of the project is to achieve the highest possible image quality and spectral stability essential for precise radial velocity measurements. The instrument also includes other observing modes which are obtained by inserting a flat mirror or a prism at different positions in the optical path. This flexibility is achieved without affecting the stability and performances of the primary, high resolution mode. We describe here the cryo-mechanical design which has been optimized to these purposes.
GIANO-TNG is an ultra-stable infrared (0.9-2.5 μm) high resolution cross-dispersed spectrometer designed to operate at a fixed position relative to the telescope axis. It therefore requires a pre-slit opto-mechanical system which takes care of field de-rotation and auto-guiding. Taking advantage of the structure already existing for SARG (the high resolution optical spectrometer of the Telescopio Nazionale Galileo, TNG) we are developing a system which provides a large (2 arcmin) field of view for offset guiding and includes, as separate and selectable elements, a gas absorption cell and a polarimetric module where the analyzers work in a collimated beam.
GIANO is a cryogenic cross-dispersed spectrometer operating at near IR wavelengths (0.9-2.5 microns). The aim of the optical design is to obtain wide spectral coverage, high resolution, large throughput and high spectral stability in a sufficiently compact instrument which can be built and cooled using relatively simple and inexpensive technologies. This ambitious goal is achieved using a 3-mirrors anastigmat in double-pass which acts both as collimator and camera. The collimated beam has a diameter of 100 mm and feeds a commercial 23.2 lines/mm echelle grating. Cross-dispersion is performed by prisms which also operate in double pass. By inserting a flat mirror before the grating, the instrument changes its face (hence the name "GIANO") and transforms into a low resolution spectrometer with a unique combination of spectral coverage, resolution and efficiency.
GIANO is an infrared (0.9-2.5 μm cross-dispersed echelle spectrometer designed to achieve high resolution, high throughput, wide band coverage and very high stability for accurate radial velocity measurements. It also includes polarimetric capabilities and a low resolution mode with RS ~ 400 and complete 0.75-2.5 μm coverage. This makes it a very versatile, common user instrument which will be permanently mounted and available on the Nasmyth-B foci of the Telescopio Nazionale Galileo (TNG) located at Roque de Los Muchachos Observatory (ORM), La Palma, Spain. The project is fast-track and relies on well known, relatively standard technologies. It has been recognized as one of the top priority instrumental projects of INAF (the Italian National Institute of Astronomy) and received its first financing for the phase-A study in October 2003. Integration in the laboratory is planned to start before the end of 2006, commissioning at the telescope is foreseen within 2007 and scientific operations in 2008. One of the most important scientific goals is the search for rocky planets with habitable conditions around low-mass stars. If completed on time, GIANO will be the first and only IR instrument operating worldwide
providing the combination of efficiency, spectral resolution, wavelength coverage and stability necessary for this type of research. With its unique combination of high and low resolution modes, GIANO will also be a very flexible common-user instrument ideal e.g. for quantitative spectroscopy of brown dwarfs, stars and stellar clusters as well as for the determination of the spectral energy distribution of faint/red objects such as high redshift galaxies. The expected limiting magnitudes are such that GIANO will be able to deliver good quality HR spectra of any 2MASS object and LR spectra of any object detected in the UKIDSS large area survey.
Giano is an infrared (0.9-2.5 μm) cross-dispersed echelle spectrometer designed to achieve high throughput, high resolving power, wide band coverage and high accuracy. Giano will be a common user instrument which will be permanently mounted at the Telescopio Nazionale Galileo (TNG), located at Roque de Los Muchachos Observatory (ORM), La Palma, Spain. Giano successfully concluded the development phase, and we present here some of the solutions adopted in the focal plane electronics, which take care of detector control and data acquisition and handling.
GIANO is an infrared (0.9-2.5 μm) cross-dispersed echelle spectrometer designed to achieve high throughput, high resolving power, wide band coverage and high accuracy radial velocity measurements. It also includes polarimetric capabilities and a low resolution mode that make it a very versatile, common user instrument which will be permanently mounted and available at one of the Nasmyth foci of the Telescopio Nazionale Galileo (TNG) located at Roque de Los Muchachos Observatory (ORM), La Palma, Spain. GIANO was selected by INAF as the top priority instrument among those proposed within the Second Generation Instrumentation Plan of the TNG. More information on this project can be found at the web page http://www.bo.astro.it/giano
The instrumentation for VLT/VLTI 1 facility of the European Southern Observatory at Paranal (Chile)includes the infrared beam-combiner called AMBER, that covers the near infrared bands up to 2.5 μm. The cold spectrograph we describe is the AMBER subsystem responsible of wavelength analysis and several other functions, all of them performed by means of optics, analyzers, and mechanisms working at the temperature of liquid nitrogen boiling at atmospheric pressure. The cryo-mechanical design of the spectrograph we describe here
used extensively the methods of finite element analysis and the laboratory tests validated this approach. The final optical quality we measured in the laboratory before shipping the instrument to Grenoble or integration (December 2002),is well inside the specification the AMBER staff assigned to the spectrograph. Simulations show that its total contribution to visibility loss of AMBER is less than 2%.
AMBER is the General User near infrared focal instrument of the Very Large Telescope Interferometer. Its a single mode, dispersed fringes, three telescopes instrument. A limiting magnitude of the order of H=13 will allow to tackle a fair sample of extra galactic targets. A very high accuracy, in particular in color differential phase and closure phase modes gives good hope for very high dynamic range observation, possibly including hot extra solar planets. The relatively high maximum spectral resolution, up to 10000, will allow some stellar activity observations. Between this extreme goals, AMBER should have a wide range of applications including Young Stellar Objects, Evolved Stars, circumstellar material and many others. This paper tries to introduce AMBER to its future users with
information on what it measures, how it is calibrated and hopes
to give the readers ideas for applications.
AMBER is a focal instrument for the Very Large Telescope Interferometer working in the near infrared from 1.1 to 2.4 micrometers . It has been designed having in mind the General User of interferometric observations and the full range of his possible astrophysical programs. However the three programs used to define the key specifications have been the study of Young Stellar Objects, the study of Active Galactic Nuclei dust tori and broad line regions and the measure of masses and spectra of hot Extra Solar Planets. AMBER combines up to three beams produced by the VLTI 8 m Unit Telescopes equipped with Adaptive Optics and/or by the 1.8 m Auxiliary Telescopes. The fringes are dispersed with resolutions ranging from 35 to 10000. It is optimized for high accuracy single mode measurements of the absolute visibility, of the variation of the visibility and phase with wavelength (differential interferometry) and of phase closure relations with three telescopes. The instrument and its software are designed to allow a highly automated user friendly operation and an easy maintenance.
AMBER, Astronomical Multi BEam combineR, is the near- infrared instrument dedicated to the VLTI. It is presently designed to work with three of either the 8 m or the 1.8 m telescopes from 1 to 2.5 micrometers . Given the expected scientific performance and requirements for AMBER, we derived the functional analysis leading to the present optical configuration using optical fibers to spatially filter the wavefront perturbations, and dispersed fringes. The expected performance is presented in terms of optical quality and sensitivity to misalignments.
We describe the general characteristics of the TIRGO infrared telescope, located on Gornergrat (Switzerland), and its most recent instrumentation. This telescope is specifically designed for infrared astronomical observations. Two newly designed instruments are presented: the imaging camera Arnica and the long-slit spectrometer LonGSp, both based on two-dimensional array detectors.
The near infrared camera/spectrometer (or NICS, for brevity), that we are currently designing for first-light operations of the Italian Telescope Galileo (TNG), makes use of a set of optics for achieving both good quality imaging on equivalent fields of view on the sky as large as 4' X 4', and moderate resolution spectroscopy at a resolving power of 400 - 2200, with the possibility to reach 7500 in the future, over the near infrared bands from 0.95 micrometers up to 2.50 micrometers . We describe the details of the optical design, with the overall requests we imposed on the project in terms of performance and total size.
We present an astronomical cooled grating spectrometer (LonGSp--Longslit Gornergrat Spectrometer) designed to work at Telescopio Infrarosso del Gornergrat. The covered spectral range is 0.9 divided by 2.5 micrometers and the resolving power is between 300 and 4000 depending on the order and slit width. The spectrometer employs a NICMOS 3 (256 X 256) engineering array of which a subsection of 70 X 40 is used.
A low-cost solution to the problem of cryogenic motors for infrared instrument is presented. Stepper motors have been modified to work in a cryogenic environment (T approximately equals 80 K) and laboratory tests have been performed to estimate both wear and torque. The modifications to the motors and the results of the measurements on torque of two different motors are reported.