Artemis(*) is an ESO PI project that aims to develop a large bolometer camera in the submillimeter range on APEX. CEA-Saclay in France is building this instrument, based on the development of new generation bolometer arrays for the PACS photometer aboard the Herschel Space Observatory. These bolometers do not use feedhorns to concentrate the submillimeter light, but act more like a CCD camera. This instrument can therefore instantaneously fully sample the image in the focal plane and does not require any "jiggling" pattern. The estimated gain in speed when mapping extended sources is ~3 compared to a classical bolometer array with feedhorns with the same sensitivity and FOV.
These bolometers, working at 300 mK, are semiconductors (all-silicon technology) and are multiplexed (16 to 1). They are background limited in the PACS instrument and should provide the same performances under ground-based conditions.
The idea of the project is to build a large bolometric focal plane (64 x 64 bolometers) working at 200, 350 and 450 microns (band selection made by a filter wheel inside the instrument). The Saclay group plans to have the Artemis camera ready at APEX at March 2011.
Visit the Artemis page at CEA here.
The image on the right shows one of the two PACS focal planes (2048 bolometers, 8 sub-arrays of 256 elements each).
The prototype : P-Artemis
A prototype (called P-Artemis) has been tested at APEX in March 2007 at 450 microns (one small array of 256 bolometers). The goal was to demonstrate the feasibility and scientific potential of the full instrument. The P-Artemis array used for these tests is a 16x16-pixel PACS-like detector array that was not selected for Herschel and was modified to operate at 450 microns by adding a silicon layer on its surface (anti-reflecting layer). A scientific run took place in November 2007 with a modified optics and resulted in an NEFD improved by a factor ~3.
This table sums up the expected (Artemis) and measured (P-Artemis) performances of the instrument.
|FOV||Beam FWHM||Pixel Size||pixel NEFD (a)|
(mJy/beam, 1sigma, 1s)
| 1.8' x 1.8' |
3.2' x 3.2'
4.1' x 4.1'
1.0' x 1.0'
|SHARC-2||350||0.9' x 2.5'||8.5"||4.8"||1000||1|
|SCUBA-2||450||8' x 8'||7.5"||6.2"||600||40|
(a) : For the Artemis case, this is the expected NEFD assuming an elevation of 50 degrees, a PWV=0.6 mm at 350 and 450 microns and PWV=0.2 mm at 200 microns.
(b) : Imaging Speed relative to SHARC-2 on the CSO at 350 microns for mapping cold dust emission. This is defined as the speed with which areas of the sky can be imaged to a given equivalent surface brightness sensitivity. The wavelength normalization assumes a dust temperature of 15K and a dust emissivity index of 1.5.
(c) : The P-Artemis' NEFD at 200 microns is estimated from the 450 microns case. Note that the P-Artemis detectors are not fully optimized for ground-based conditions as they use spare arrays not selected for Herschel.
(*) Artemis stands for "Architectures de bolometres pour des Telescopes a grand champ de vue dans le domaine sub-Millimetrique au Sol" in French.