Michel Talvard

Submillimetre/TeraHertz Astronomy at Dome C with CEA Filled Bolometer Array

Submillimetre/TeraHertz (e.g. 200, 350, 450 microns) astronomy is the prime technique to unveil the birth and early evolution of a broad range of astrophysical objects. A major obstacle to carry out submm observations from ground is the atmosphere. Preliminary site testing and atmospheric transmission models tend to demonstrate that Dome C could offer the best conditions on Earth for submm/THz astronomy. The CAMISTIC project aims to install a filled bolometer-array camera with 16x16 pixels on IRAIT at Dome C and explore the 200-

The ArTéMiS wide-field sub-millimeter camera: preliminary on-sky performance at 350 microns

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Toward a large telescope facility for submm/FIR astronomy at Dome C

m windows for potential ground-based observations.

TALC: a new deployable concept for a 20m far-infrared space telescope

ArTeMiS is a wide-field submillimeter camera operating at three wavelengths simultaneously (200, 350 and 450 μm). A preliminary version of the instrument equipped with the 350 μm focal plane, has been successfully installed and tested on APEX telescope in Chile during the 2013 and 2014 austral winters. This instrument is developed by CEA (Saclay and Grenoble, France), IAS (France) and University of Manchester (UK) in collaboration with ESO. We introduce the mechanical and optical design, as well as the cryogenics and electronics of the ArTéMiS camera. ArTeMiS detectors consist in Si:P:B bolometers arranged in 16×18 sub-arrays operating at 300 mK. These detectors are similar to the ones developed for the Herschel PACS photometer but they are adapted to the high optical load encountered at APEX site. Ultimately, ArTeMiS will contain 4 sub-arrays at 200 μm and 2×8 sub-arrays at 350 and 450 μm. We show preliminary lab measurements like the responsivity of the instrument to hot and cold loads illumination and NEP calculation. Details on the on-sky commissioning runs made in 2013 and 2014 at APEX are shown. We used planets (Mars, Saturn, Uranus) to determine the flat-field and to get the flux calibration. A pointing model was established in the first days of the runs. The average relative pointing accuracy is 3 arcsec. The beam at 350 μm has been estimated to be 8.5 arcsec, which is in good agreement with the beam of the 12 m APEX dish. Several observing modes have been tested, like “On- The-Fly” for beam-maps or large maps, spirals or raster of spirals for compact sources. With this preliminary version of ArTeMiS, we concluded that the mapping speed is already more than 5 times better than the previous 350 μm instrument at APEX. The median NEFD at 350 μm is 600 mJy.s1/2, with best values at 300 mJy.s1/2. The complete instrument with 5760 pixels and optimized settings will be installed during the first half of 2015.

ArTeMiS: filled bolometer arrays for next-generation sub-mm telescopes

Submillimetre astronomy is the prime technique to unveil the birth and early evolution of stars and galaxies in the local and distant Universe. Preliminary meteorological studies and atmospheric transmission models tend to demonstrate that Dome C might offer atmosphere conditions that open the 200-μm atmospheric windows, and could potentially be a site for a large ground-based telescope facility. However, Antarctic climate conditions might also severely impact and deform any telescope mirror and hardware. We present prerequisite conditions and their associate experiments for defining a large telescope facility for submillimetre astronomy at Dome C: (1) Whether the submm/THz atmospheric windows open from 200 μm during a large and stable fraction of time; (2) The knowledge of thermal gradient and (3) icing formation and their impact on a telescope mirror and hardware. This paper will present preliminary results on current experiments that measure icing, thermal gradient and sky opacity at Dome C. We finally discuss a possible roadmap toward the deployment of a large telescope facility at Dome C.

Status of the ArTeMiS camera to be installed on APEX

TALC, Thin Aperture Light Collector is a 20 m space observatory project exploring some unconventional optical solutions (between the single dish and the interferometer) allowing the resolving power of a classical 27 m telescope. With TALC, the principle is to remove the central part of the prime mirror dish, cut the remaining ring into 24 sectors and store them on top of one-another. The aim of this far infrared telescope is to explore the 600 μm to 100 μm region. With this approach we have shown that we can store a ring-telescope of outer diameter 20m and ring thickness of 3m inside the fairing of Ariane 5 or Ariane 6. The general structure is the one of a bicycle wheel, whereas the inner sides of the segments are in compression to each other and play the rule of a rim. The segments are linked to each other using a pantograph scissor system that let the segments extend from a pile of dishes to a parabolic ring keeping high stiffness at all time during the deployment. The inner corners of the segments are linked to a central axis using spokes as in a bicycle wheel. The secondary mirror and the instrument box are built as a solid unit fixed at the extremity of the main axis. The tensegrity analysis of this structure shows a very high stiffness to mass ratio, resulting into 3 Hz Eigen frequency. The segments will consist of two composite skins and honeycomb CFRP structure build by replica process. Solid segments will be compared to deformable segments using the controlled shear of the rear surface. The adjustment of the length of the spikes and the relative position of the side of neighbor segments let control the phasing of the entire primary mirror. The telescope is cooled by natural radiation. It is protected from sun radiation by a large inflatable solar screen, loosely linked to the telescope. The orientation is performed by inertia-wheels. This telescope carries a wide field bolometer camera using cryocooler at 0.3K as one of the main instruments. This telescope may be launched with an Ariane 6 rocket up to 800 km altitude, and use a plasma stage to reach the Lagrange 2 point within 18 month. The plasma propulsion stage is a serial unit also used in commercial telecommunication satellites. When the plasma launch is completed, the solar panels will be used to provide the power for communication, orientation and power the cryo-coolers for the instruments. The guide-line for development of this telescope is to use similar techniques and serial subsystems developed for the satellite industry. This is the only way to design and manufacture a large telescope at a reasonable cost.

Recent results obtained on the APEX 12 m antenna with the ArTeMiS prototype camera

Astronomical observations at sub-millimetre wavelengths are limited either by the angular resolution of the telescope or by the sensitivity and field of view of the detector array. New generation of radio telescopes, such as the ALMA-type antennas on Chajnantor plateau in Chile, can overcome these limitations if they are equipped with large detector arrays made of thousands of sensitive bolometer pixels. Instrumentation developments undertaken at CEA and based on the all silicon technology of CEA/Leti are able to provide such large detector arrays. The ArTeMiS project consists in developing a camera for ground-based telescopes that operates in two sets of atmospheric windows at 200-450 μm (channel 1) and 800-1200 μm (channel 2). ArTeMiS-1 consists in grid bolometer arrays similar to those developed by CEA for the Herschel Space Observatory. A prototype camera operating in this first atmospheric window was installed and successfully tested in March 2006 on the KOSMA telescope at Gornergrat (Switzerland) in collaboration with the University of Cologne. ArTeMiS-2 will consist either in antenna-coupled bolometer arrays or specific mesh bolometer arrays. By the end of 2008, ArTeMiS cameras could be operated on 10m-class telescopes on the Chajnantor ALMA site, e.g., APEX, opening new scientific prospects in the study of the early phases of star formation and in cosmology, in the study of the formation of large structures in the universe. At longer term, installation of such instrumentation at Dome-C in Antarctica is also under investigation. The present status of the ArTeMiS project is detailed in this paper.

CAMISTIC: THz/submm astronomy at Dome C in Antarctica

The ArTeMiS submillimetric camera will observe simultaneously the sky at 450, 350 and 200 μm using 3 different focal planes made of 2304, 2304 and 1152 bolometric pixels respectively. This camera will be mounted in the Cassegrain cabin of APEX, a 12 m antenna located on the Chajnantor plateau, Chile. To realize the bolometric arrays, we have adapted the Silicon processing technology used for the Herschel-PACS photometer to account for higher incident fluxes and longer wavelengths from the ground. In addition, an autonomous cryogenic system has been designed to cool the 3 focal planes down to 300 mK. Preliminary performances obtained in laboratory with the first of 3 focal planes are presented. Latest results obtained in 2009 with the P-ArTeMiS prototype camera are also discussed, including massive protostellar cores and several star forming regions that have been clearly identified and mapped.

Cryogenic system for the ArTeMiS large sub millimeter camera

ArTeMiS is a camera designed to operate on large ground based submillimetric telescopes in the 3 atmospheric windows 200, 350 and 450 µm. The focal plane of this camera will be equipped with 5760 bolometric pixels cooled down at 300 mK with an autonomous cryogenic system. The pixels have been manufactured, based on the same technology processes as used for the Herschel-PACS space photometer. We review in this paper the present status and the future plans of this project. A prototype camera, named P-ArTeMiS, has been developed and successfully tested on the KOSMA telescope in 2006 at Gornergrat 3100m, Switzerland. Preliminary results were presented at the previous SPIE conference in Orlando (Talvard et al, 2006). Since then, the prototype camera has been proposed and successfully installed on APEX, a 12 m antenna operated by the Max Planck Institute für Radioastronomie, the European Southern Observatory and the Onsala Space Observatory on the Chajnantor site at 5100 m altitude in Chile. Two runs have been achieved in 2007, first in March and the latter in November. We present in the second part of this paper the first processed images obtained on star forming regions and on circumstellar and debris disks. Calculated sensitivities are compared with expectations. These illustrate the improvements achieved on P-ArTeMiS during the 3 experimental campaigns.

Latest results and prospects of the ArTeMiS camera on APEX

Submillimetre (submm) astronomy is the prime technique to unveil the birth and early evolution of a broad range of astrophysical objects. It is a relatively new branch of observational astrophysics which focuses on studies of the cold Universe, i.e., objects radiating a significant − if not dominant − fraction of their energy at wavelengths ranging from ∼ 100μm to ∼ 1mm. Submm continuum observations are particularly powerful to measure the luminosities, temperatures and masses of cold dust emitting objects. Examples of such objects include star-forming clouds in our Galaxy, prestellar cores and deeply embedded protostars, protoplanetary disks around young stars, as well as nearby starburst galaxies and dust-enshrouded high-redshift galaxies in the early Universe. A major obstacle to carry out submm observations from ground is the atmosphere. Astronomical observations in the submm spectral bands can only be achieved from extremely cold, dry and stable sites (e.g., high altitude plateau, Antarctica) or from space (e.g., the Herschel Space Observatory) to overcome the atmosphere opacity and instability that are mainly due to water vapour absorption and fluctuation in the low atmosphere. Chile currently offers the best accessible (all-year long) sites on Earth, where the precipitable water vapour (PWV) content is often less than 1mm. Chile hosts the best astronomical facilities such as ESO VLT, APEX and Chajnantor plateau will be the ALMA site. At longer term, and particularly if global warming severely restricts the 200 – 350 – 450μm windows on ESO sites, Antarctica conditions with less than 0.2mm PWV, could offer an exciting alternative for THz/submm astronomy (Fig. 1). This is an attractive opportunity for the 200μm windows, especially, which are normally explored with space telescopes (e.g., Herschel). Observations of submm continuum emission are usually carried out with bolometer detectors. Recently, two Research Departments at CEA (DSM/DAPNIA/SAp and DRT/LETI/LIR) developped filled bolometer arrays for the PACS submm/far-infrared imager on the Herschel Space Observatory, to be launched by ESA in 2007. The R&D was based on a unique and innovating technology that combines all silicon technology (resistive thermometers, absorbing grids, multiplexing) and monolithic fabrication. The bolometers are assembled on a mosaic ‘CCD-like’ array that provides full sampling of the focal plane with ∼ 2,000 pixels that are arranged in units of 256 pixels. They are cooled down to 300mK to optimise the sensitivity down to the physical limit imposed by the photon background noise. The PACS bolometer arrays have passed all the qualification tests (Billot et al. 2006). The newly started ArTeMiS project at CEA Saclay capitalises on this achievement by developing submm (200 – 450μm) bolometer arrays with ∼ 4,000 pixels for ground-based telescopes. A prototype camera operating in the 450μm