L. Lessio

Qualification and Testing of a Large Hot Slumped Secondary Mirror for Schwarzschild–Couder Imaging Air Cherenkov Telescopes

Dual-mirror Schwarzschild–Couder (SC) telescopes are based on highly aspherical optics, and they represent a novel design in the world of very high energy astrophysics. This work addresses the realization and the qualification of the secondary mirror for an SC telescope, named ASTRI, developed in the context of the Cherenkov Telescope Array Observatory. The discussion surveys the overall development from the early design concept to the final acceptance optical tests.

Status of the technologies for the production of the Cherenkov telescope array (CTA) mirrors

The Cherenkov Telescope Array (CTA) is the next generation very high-energy gamma-ray observatory, with at least 10 times higher sensitivity than current instruments. CTA will comprise several tens of Imaging Atmospheric Cherenkov Telescopes (IACTs) operated in array-mode and divided into three size classes: large, medium and small telescopes. The total reflective surface could be up to 10,000 m2 requiring unprecedented technological efforts. The properties of the reflector directly influence the telescope performance and thus constitute a fundamental ingredient to improve and maintain the sensitivity. The R&D status of lightweight, reliable and cost-effective mirror facets for the CTA telescope reflectors for the different classes of telescopes is reviewed in this paper.

Optical Design and Test of the BIGRE Based IFS of SPHERE

During the last months IFS, is the Integral Field Spectrograph for SPHERE, devoted to the search of exoplanets has been integrated in the clean room of Padova Observatory. The design of IFS is based on a new concept of double microlens array sampling the focal plane. This device named BIGRE consists of a system made of two microlens arrays with different focal lengths and thickness equal to the sum of them and precisely aligned each other. Moreover a mask has been deposited on the first array to produce a field stop for each lenslet, and a second mask is located on the intermediate pupil of the IFS to provide an aperture stop. After characterization of a previous prototype of BIGRE in the visible range, now the first measurements of the performances of the device in the IR range have been obtained on the instrument that will be mounted at the VLT telescope. These tests confirmed that specifications and properties of the prototype are met by state of the art on optics microlens manufacturing.

The SPHERE IFS at work

SPHERE is an extrasolar planet imager whose goal is to detect giant extrasolar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made of an extreme-Adaptive Optics (AO) turbulence correction, a pupil tracker and NIR and Visible coronagraph devices. At its back end, a differential dual imaging camera and an integral field spectrograph (IFS) work in the Near Infrared (NIR) (0.95 ≤λ≤2.32 μm) and a high resolution polarization camera covers the visible (0.6 ≤λ≤0.9 μm). The IFS is a low resolution spectrograph (R~50) operates in the near IR (0.95≤λ≤1.6 μm), an ideal wavelength range for the detection of planetary features, over a field of view of about 1.7 x 1.7 square arcsecs. Form spectra it is possible to reconstruct monochromatic images with high contrast (10-7) and high spatial resolution, well inside the star PSF. In this paper we describe the IFS, its calibration and the results of several performance which IFS underwent. Furthermore, using the IFS characteristics we give a forecast on the planetary detection rate.

A facility to evaluate the focusing performance of mirrors for Cherenkov Telescopes

Abstract Cherenkov Telescopes are equipped with optical dishes of large diameter – in general based on segmented mirrors – with typical angular resolution of a few arc-minutes. To evaluate the mirror׳s quality specific metrological systems are required that possibly take into account the environmental conditions in which typically these telescopes operate (in open air without dome protection). For this purpose a new facility for the characterization of mirrors has been developed at the labs of the Osservatorio Astronomico di Brera of the Italian National Institute of Astrophysics. The facility allows the precise measurement of the radius of curvature and the distribution of the concentred light in terms of focused and scattered components and it works in open air. In this paper we describe the facility and report some examples of its measuring capabilities.

The ASTRI SST-2M prototype for the next generation of Cherenkov telescopes: structure and mirrors

The next generation of Imaging Atmospheric Cherenkov Telescope will explore the uppermost end of the Very High Energy domain up to about few hundreds of TeV with unprecedented sensitivity, angular resolution and imaging quality. To this end, the Italian National Institute of Astrophysics (INAF) is currently developing a scientific and technological telescope prototype for the implementation of the Cherenkov Telescope Array (CTA) observatory. The Italian ASTRI program foresees the full design, development, installation and calibration of a Small Size 4-meter class Telescope, adopting an aplanatic, wide-field, double-reflection optical layout in a Schwarzschild-Couder configuration. In this paper we discuss about the technological solutions adopted for the telescope and for the mirrors. In particular we focus on the structural and electro-mechanical design of the telescope, now under fabrication. The results on the optical performance derived from mirror prototypes are here described, too.

Techniques for the manufacturing of stiff and lightweight optical mirror panels based on slumping of glass sheets: concepts and results

In the last decade Very High Energy (VHE) gamma-ray astronomy has improved rapidly opening a new window for ground-based astronomy with surprising implications in the theoretical models. Nowadays, it is possible to make imaging, photometry and spectroscopy of sources with good sensitivity and angular resolution using new facilities as MAGIC, HESS and VERITAS. The latest results of astronomy in the TeV band obtained using such facilities demonstrate the essential role of this window for high energy astrophysics. For this reason new projects (e.g. CTA and AGIS) have been started with the aim to increase the sensitivity and expand the energy band coverage. For such telescopes arrays probably tens of thousands of optical mirror panels must be manufactured with an adequate industrial process, then tested and mounted into the telescopes. Because of the high number of mirrors it is mandatory to perform feasibility studies to test various techniques to meet the technical and cost-effectiveness requirements for the next generation TeV telescopes as CTA and AGIS. In this context at the Astronomical Observatory of Brera (INAF-OAB) we have started the investigation of different techniques for the manufacturing of stiff and lightweight optical glass mirror panels. These panels show a sandwich-like structure with two thin glass skins on both sides, the reflective one being optically shaped using an ad-hoc slumping procedure. The technologies here presented can be addressed both for primary or secondary mirrors for the next generation of Cherenkov telescopes. In this paper we present and discuss the different techniques we are investigating with some preliminary results obtained from test panels realized.

New spectro-photometric characterization of the substellar object HR2562B using SPHERE

HR2562 is an F5V star located at ~33 pc from the Sun hosting a substellar companion that was discovered using the GPI instrument. The main objective of the present paper is to provide an extensive characterisation of the substellar companion, by deriving its fundamental properties. We observed HR 2562 with the near-infrared branch (IFS and IRDIS) of SPHERE at the VLT. During our observations IFS was operating in the YJ band, while IRDIS was observing with the

Intensity interferometry with Aqueye+ and Iqueye in Asiago

H

Tests characterization and alignment for the optics of the ASTRI SST-2M telescope prototype for the Cherenkov Telescope Array

broad-band filter. The data were reduced with the dedicated SPHERE GTO pipeline, which is custom-designed for this instrument. On the reduced images, we then applied the post-processing procedures that are specifically prepared to subtract the speckle noise. The companion is clearly detected in both IRDIS and IFS datasets. We obtained photometry in three different spectral bands. The comparison with template spectra allowed us to derive a spectral type of T2-T3 for the companion. Using both evolutionary and atmospheric models we inferred the main physical parameters of the companion obtaining a mass of 32+/-14