Igor Di Varano

The International Robotic Antarctic Infrared Telescope (IRAIT)

Thanks to exceptional coldness, low sky brightness and low content of water vapour of the above atmosphere Dome C, one of the three highest peaks of the large Antarctic plateau, is likely to be the best site on Earth for thermal infrared observations (2.3-300 μm) as well as for the far infrared range (30 μm-1mm). IRAIT (International Robotic Antarctic Infrared Telescope) will be the first European Infrared telescope operating at Dome C. It will be delivered to Antarctica at the end of 2006, will reach Dome C at the end of 2007 and the first winter-over operation will start in spring 2008. IRAIT will offer a unique opportunity for astronomers to test and verify the astronomical quality of the site and it will be a useful test-instrument for a new generation of Antarctic telescopes and focal plane instrumentations. We give here a general overview of the project and of the logistics and transportation options adopted to facilitate the installation of IRAIT at Dome C. We summarize the results of the electrical, electronics and networking tests and of the sky polarization measurements carried out at Dome C during the 2005-2006 summer-campaign. We also present the 25 cm optical telescope (small-IRAIT project) that will installed at Dome C during the Antarctic summer 2006-2007 and that will start observations during the 2007 Antarctic winter when a member of the IRAIT collaboration will join the Italian-French Dome C winter-over team.

ELT-HIRES the high resolution spectrograph for the ELT: optical design studies for the polarimetric unit

We present the optical design of the ELT polarimeter in the context of the Phase-A study for HIRES. It is well known that in order to reduce the instrumental polarization and cross-talk, the optimal position for a polarimeter along the optical path of a telescope is the rotationally symmetric focus. In the particular case of ELT this is represented by the intermediate focus (IF) below M4 which is not directly accessible and needs therefore a reimaging to a safety distance of at least 500 mm. The design of a transfer optics unit for such location is challenging due to the constraint of having an allowed vignetting area of maximum 5 arc min. We focus in our paper on two optical design solutions. The first one is deploying a double Cassegrain system to reimage the IF, which includes the polarization optics and feeds the other ELT mirrors, redirecting the ordinary and extraordinary beams to the front end module (FE) onto the Nasmyth focus. This module comprises components for sky derotation, atmospheric dispersion correction (ADC), wavelength splitting in two bands (UBVRI, zYJH), field stabilization and conversion to f/20, dispatching the light into two pairs of fiber bundles to feed the HIRES spectrograph. The other solution considers a fiber based compact IF module, using a Schwarzschild Collimator with Foster prism, ADC and beam splitters for the two spectral bands. The two polarized beams are sent by pupil imaging through four separate long fibers to the fiber link module of the spectrograph. There we convert the output fiber f ratio from f/2.5 to f/20.

ELT high resolution spectrograph: phase-A software architecture study

High resolution spectroscopy has been considered of a primary importance to exploit the main scientific cases foreseen for ESO ELT, the Extremely Large Telescope, the future largest optical-infrared telescope in the world. In this context ESO commissioned a Phase-A feasibility study for the construction of a high resolution spectrograph for the ELT, tentatively named HIRES. The study, which lasted 1.5 years, started on March 2016 and was completed with a review phase held at Garching ESO headquarters with the aim to assess the scientific and technical feasibility of the proposed instrument. One of the main tasks of the study is the architectural design of the software covering all the aspects relevant to control an astronomical instrument: from observation preparation through instrument hardware and detectors control till data reduction and analysis. In this paper we present the outcome of the Phase-A study for the proposed HIRES software design highlighting its peculiarities, critical areas and performance aspects for the whole data flow. The End-toEnd simulator, a tool already capable of simulating HIRES end products and currently being used to drive some design decision, is also shortly described.

ELT -HIRES, the high resolution spectrograph for the ELT; the end-to-end simulator: design approach and results.

We present the updated design and architecture of the End-to-End simulator model of the high resolution spectrograph HIRES for the future Extremely Large Telescope (ELT). The model allows to simulate the propagation of photons starting from the scientific object of interest up to the detector, allowing to evaluate the performance impact of the different parameters in the spectrograph design. The model also includes a calibration light module, suitable to evaluate data reduction requirements. In this paper, we will detail the architecture of the simulator and the computational model which are strongly characterized by modularity and flexibility that will be crucial in the next generation instrumentation for projects such as the ELT due to of the high complexity and long-time design and development. We also highlight the Cloud Computing Architecture adopted for this software based on Amazon Web Services (AWS). We also present synthetic images obtained with the current version of the End-to-End simulator based on the requirements for ELTHIRES (especially high radial velocity accuracy) that are then ingested in the Data reduction Software (DRS) of CRIRES+ as case study.

ELT-HIRES the high resolution spectrograph for the ELT: phase-A design of its polarimetric unit

The Phase A study for the high-resolution spectrograph for the Extremely Large Telescope (ELT-HIRES) has been concluded in late 2017. We present the main outcome for a polarimetric light feed from the intermediate focus (IF) and a Nasmyth focus of the telescope. We conclude that the use of the IF is mandatory for high-precision spectropolarimetry. Among the description of the product tree, we present phase-A level opto-mechanical designs of the subunits, describe the observational and calibration modes, the PSF error budget, and the preliminary FEM structural and earthquake analysis. An update on the development of a ray tracing polarimetric simulator to estimate the instrumental polarization including both the telescope mirrors and the optical elements of the polarimeter is reported. Trade-off strategies and ongoing solutions in view of the Phase B are outlined too.

AMICA (Antarctic Multiband Infrared Camera) project

The Antarctic Plateau offers unique opportunities for ground-based Infrared Astronomy. AMICA (Antarctic Multiband Infrared CAmera) is an instrument designed to perform astronomical imaging from Dome-C in the near- (1 - 5 μm) and mid- (5 - 27 μm) infrared wavelength regions. The camera consists of two channels, equipped with a Raytheon InSb 256 array detector and a DRS MF-128 Si:As IBC array detector, cryocooled at 35 and 7 K respectively. Cryogenic devices will move a filter wheel and a sliding mirror, used to feed alternatively the two detectors. Fast control and readout, synchronized with the chopping secondary mirror of the telescope, will be required because of the large background expected at these wavelengths, especially beyond 10 μm. An environmental control system is needed to ensure the correct start-up, shut-down and housekeeping of the camera. The main technical challenge is represented by the extreme environmental conditions of Dome C (T about -90 °C, p around 640 mbar) and the need for a complete automatization of the overall system. AMICA will be mounted at the Nasmyth focus of the 80 cm IRAIT telescope and will perform survey-mode automatic observations of selected regions of the Southern sky. The first goal will be a direct estimate of the observational quality of this new highly promising site for Infrared Astronomy. In addition, IRAIT, equipped with AMICA, is expected to provide a significant improvement in the knowledge of fundamental astrophysical processes, such as the late stages of stellar evolution (especially AGB and post-AGB stars) and the star formation.

Integration of a thermo-structural analysis with an optical model for PEPSI polarimeter

The two spectropolarimeters for PEPSI (Potsdam Echelle Polarimetric and Spectroscopic Instrument) have been de¬signed in order to reconstruct the full Stokes vector measuring linear and circular polarization simultaneously with a re¬solving power of 120,000. The polarimeters will be attached to the Gregorian focus of the so far largest LBT 2x8.4m telescope and will feed together with permanent focus stations the spectrograph via 44m long fibers connection. The spectrograph will be located in a pressure-temperature controlled chamber within the telescope pier. We present hereafter the last results from combined structural and CFD analyses in order to fulfill the optical requirements.

AMICA – the infrared eye at Dome C

Alberto Riva1, Mauro Dolci2, Oscar Straniero2, Filippo Maria Zerbi1, Emilio Molinari1, Paolo Conconi1, Vincenzo De Caprio1, Gaetano Valentini2, Gianluca Di Rico2, Maurizio Ragni2, Danilo Pelusi2, Igor Di Varano2, Croce Giuliani2, Amico Di Cianno2, Angelo Valentini2, Favio Bortoletto3, Maurizio D’Alessandro3, Carlotta Bonoli3, Enrico Giro3, Daniela Fantinel3, Demetrio Magrin3, Leonardo Corcione4, Maurizio Busso5, Gino Tosti5, Giuliano Nucciarelli5, Fabio Roncella5, Carlos Abia6 and the IRAIT Team 1 INAF Osservatorio Astronomico di Brera – Merate, Merate, Italy 2 INAF Osservatorio Astronomico Collurania Teramo, Teramo, Italy 3 INAF Osservatorio Astronomico di Padova, Padova, Italy 4 INAF Osservatorio Astronomico di Torino, Torino, Italy University of Perugia, Perugia, Italy University of Granada, Granada, Spain