Leonardo Corcione

The VLTI fringe sensors: FINITO and PRIMA FSU

FINITO is the first generation VLTI fringe sensor, optimised for three beam observations, recently installed at Paranal and currently used for VLTI optimisation. The PRIMA FSU is the second generation, optimised for astrometry in dual-feed mode, currently in construction. We discuss the constraints of fringe tracking at VLTI, the basic functions required for stabilised interferometric observations, and their different implementation in the two instruments, with remarks on the most critical technical aspects. We provide an estimate of the expected performance and describe some of their possible observing and calibration modes, with reference to the current scientific combiners.

Mid-Infrared Photometry of Mass-losing Asymptotic Giant Branch Stars

We present ground-based mid-IR imaging for 27 M-, S-, and C-type asymptotic giant branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS, Infrared Space Observatory, Midcourse Space Experiment, and Two Micron All Sky Survey catalogs. Our goal is to establish relations between the IR colors, the effective temperature Teff, the luminosity L, and the mass-loss rate , for improving the effectiveness of AGB modeling. Bolometric (absolute) magnitudes are obtained through distance compilations and by applying previously derived bolometric corrections; the variability is also studied, using data accumulated since the IRAS epoch. The main results are as follows: (1) Values of L and for C stars fit relations previously established by us, with Mira variables being on average more evolved and mass-losing than semiregular variables. (2) Moderate IR excesses (as compared to evolutionary tracks) are found for S and M stars in our sample: they are confirmed to originate from the dusty circumstellar environment. (3) A larger reddening characterizes C-rich Mira variables and post-AGB stars. In this case, part of the excess is due to AGB models overestimating Teff for C stars, as a consequence of the lack of suitable molecular opacities. This has a large effect on the colors of C-rich sources, and sometimes disentangling the photospheric and circumstellar contributions is difficult; better model atmospheres should be used in stellar evolutionary codes for C stars. (4) The presence of a long-term variability at mid-IR wavelengths seems to be limited to sources with maximum emission in the 8-20 μm region, usually Mira variables (one-third of our sample). Most of the semiregular and post-AGB stars studied here have remained remarkably constant in the mid-IR over the last 20 years.

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.

The x-ray microcalorimeter spectrometer onboard Athena

One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena. In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given.

Euclid near-infrared spectrophotometer instrument concept at the end of the phase A study

The Euclid mission objective is to map the geometry of the dark Universe by investigating the distance-redshift relationship and the evolution of cosmic structures. The NISP (Near Infrared Spectro-Photometer) is one of the two Euclid instruments operating in the near-IR spectral region (0.9-2μm). The instrument is composed of: - a cold (140K) optomechanical subsystem constituted by a SiC structure, an optical assembly, a filter wheel mechanism, a grism wheel mechanism, a calibration unit and a thermal control - a detection subsystem based on a mosaic of 16 Teledyne HAWAII2RG 2.4μm. The detection subsystem is mounted on the optomechanical subsystem structure - a warm electronic subsystem (280K) composed of a data processing / detector control unit and of an instrument control unit. This presentation will describe the architecture of the instrument, the expected performance and the technological key challenges. This paper is presented on behalf of the Euclid Consortium.

System overview of the VLTI Spectro-Imager

The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility. The concept of VSI consists on 6 sub-systems: a common path distributing the light between the fringe tracker and the scientific instrument, the fringe tracker ensuring the co-phasing of the array, the scientific instrument delivering the interferometric observables and a calibration tool providing sources for internal alignment and interferometric calibrations. The two remaining sub-systems are the control system and the observation support software dedicated to the reduction of the interferometric data. This paper presents the global concept of VSI science path including the common path, the scientific instrument and the calibration tool. The scientific combination using a set of integrated optics multi-way beam combiners to provide high-stability visibility and closure phase measurements are also described. Finally we will address the performance budget of the global VSI instrument. The fringe tracker and scientific spectrograph will be shortly described.

The on-board electronics for the near infrared spectrograph and photometer (NISP) of the EUCLID Mission

The Near Infrared Spectrograph and Photometer (NISP) is one of the instruments on board the EUCLID mission. The focal plane array (FPA) consists of 16 HAWAII-2RG HgCdTe detectors from Teledyne Imaging Scientific (TIS), for NIR imaging in three bands (Y, J, H) and slitless spectroscopy in the range 0.9−2µm. Low total noise measurements (i.e. total noise < 8 electrons) are achieved by operating the detectors in multiple non-destructive readout mode for the implementation of both the Fowler and Up-The-Ramp (UTR) sampling, which also enables the detection and removal of cosmic ray events. The large area of the NISP FPA and the limited satellite telemetry available impose to perform the required data processing on board, during the observations. This requires a well optimized on-board data processing pipeline, and high-performance control electronics, suited to cope with the time constraints of the NISP acquisition sequences. This paper describes the architecture of the NISP on-board electronics, which take charge of several tasks, including the driving of each individual HAWAII-2RG detectors through their SIDECAR ASICs, the data processing, inclusive of compression and storage, and the instrument control tasks. We describe the implementation of the processing power needed for the demanding on-board data reduction. We also describe the basic operational modes that will be managed by the system during the mission, along with data flow and the Telemetry/TeleCommands flow. This paper reports the NISP on-board electronics architecture status at the end of the Phase B1, and it is presented on behalf of the Euclid Consortium.

VSI: the VLTI spectro-imager

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R = 12000. Targets as faint as K = 13 will be imaged without requiring a brighter nearby reference object; fainter targets can be accessed if a suitable reference is available. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysics. The high level specifications of the instrument are derived from a detailed science case based on the capability to obtain, for the first time, milliarcsecond-resolution images of a wide range of targets including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return.

The E-NIS instrument on-board the ESA Euclid Dark Energy Mission: a general view after positive conclusion of the assesment phase

The Euclid Near-Infrared Spectrometer (E-NIS) Instrument was conceived as the spectroscopic probe on-board the ESA Dark Energy Mission Euclid. Together with the Euclid Imaging Channel (EIC) in its Visible (VIS) and Near Infrared (NIP) declinations, NIS formed part of the Euclid Mission Concept derived in assessment phase and submitted to the Cosmic Vision Down-selection process from which emerged selected and with extremely high ranking. The Definition phase, started a few months ago, is currently examining a substantial re-arrangement of the payload configuration due to technical and programmatic aspects. This paper presents the general lines of the assessment phase payload concept on which the positive down-selection judgments have been based.

Autonomous operations in extreme environments: the AMICA case

An autonomous observatory is being installed at Dome C in Antarctica. It will be constituted by the International Robotic Antarctic Infrared Telescope (IRAIT) and the Antarctic Multiband Infrared CAmera (AMICA). Because of the extreme environment, the whole system has been developed to operate robotically, paying particular attention to the environmental conditions and the subsystems activity monitoring. A detailed description of the IRAIT/AMICA data acquisition process and management will be shown, focusing on automated procedures and solutions against safety risks.