Archeops flights and first results

A first flight of the instrument took place in Trapani on July 17th 1999. This test flight used only a few detectors (5) and we got only 4 hours of data during the night. Nevertheless, this flight allowed us to check all the fonctionnalities of the instrument [1]. Preliminary results concerning the Galactic Plane emission are shown by Boulanger et al. (this conference).

One flight was successful at the end of the Dec 2000-Jan 2001 campaign in Kiruna (Sweden), on the 29th January 2001; it lasted 7h30 at a 32 km altitude. Very high stratospheric winds limited both the flight duration and the altitude. The (sub)millimetre beams could be measured during the flight when the telescope crossed Jupiter twice and are as expected (optical beam of 8 arcmin. at 143, 217 and 545 GHz and 6 arcmin. at 353 GHz). The 143 and 217 GHz signals are dominated by the cosmic dipole and the 10 K back-to-back horn emission (sinusoidal shape). At 353 and 545 GHz, the emission from the Galaxy is dominant as well as some atmospheric signal. A significant fraction of the sky could be observed (22%) albeit with a small zone covered twice. The galactic plane is well observed at all frequencies from the anticenter to the Cygnus regions. Some clouds much below the Galactic plane can easily be identified with their CO and infrared counterparts (Perseus, Taurus, Pleiades). In-flight calibrations with the CMB dipole and the Galaxy as measured by COBE-FIRAS agree within 10% of each other. Sensitivity to cirrus HI clouds is estimated at 545 GHz as $2\times 10^{20}\hbox{$\,{\rm H\, cm^{-2}}\,$}(\theta/1\rm\,deg)^{-1}$ ($1\ \sigma$) for square areas with an angular side of $\theta$ and standard dust emissivities.

With the 353 GHz channels, Archeops will provide the first measurement of galactic polarized emission in this type of frequencies. It is an important topic in the prospect of foreground removal for Planck-HFI, and is also of great interest to constrain the physics of galactic dust and molecular clouds. The sensitivity for the current flight is a degree of 5% polarisation ($1\ \sigma$) for $A_V=15$ in a one-square degree patch. Sensitivities are typically between 50 and $100\rm\,\mu K_{RJ}$ for one second of integration and for one photometric pixel at 143 and 217 GHz. There are about 8 pixels with a CMB sensitivity between 120 and $200 \rm\,\mu K_{CMB}$ for one second of integration and for one photometric pixel.

Good detections of the CMB anisotropy spectrum can be expected from large angular scales to beyond the first so-called acoustic peak. This work is currently in progress. Archeops should also be able to constrain dust emissivity laws in the many galactic regions that were not resolved by FIRAS (a hotly debated issue in this conference). Another specific benefit from Archeops is to connect, in the spherical harmonic $l$-space sense, the calibration of the FIRAS low resolution all-sky (sub)millimetre survey up to the high resolution small area observations from ground telescopes.

The development of this current Archeops project owes a lot to the pionneering work and enthusiasm of Guy Serra in the domain of submillimetre astronomy. We also wish to thank the CNES and Esrange Swedish Facility for their continued support for this project and the flights (technical and scientific) that were realised very smoothly.