Guy Serra

First Measurement of the Submillimeter Sunyaev-Zeldovich Effect

We report the first detection of the Sunyaev-Zeldovich (S-Z) increment on the cosmic microwave background at submillimeter wavelengths in the direction of a cluster of galaxies. It was achieved toward the rich cluster Abell 2163, using the PRONAOS 2 m stratospheric telescope. Together with data from the SuZIE, Diabolo, and ISO-PHT experiments, these measurements, for the first time, give a complete picture of the far-infrared-to-millimeter spectral energy distribution of the diffuse emission toward a cluster of galaxies. It clearly shows the positive and negative parts of the S-Z effect and also a positive signal at short wavelengths that can be attributed to foreground dust in our Galaxy.

Evaluation of the role of organometallic species in the chemistry of interstellar and circumstellar media

Interactions between metal atoms or ions and unsaturated organic molecules in the interstellar or circumstellar media could play an important role in the chemistry of these media.Ab‐initio calculations were performed to predict bonding energy of the cations [metal‐benzene]+ and [Mg‐pyrene]+. We showed that the higher bonding energy of [metal‐benzene]+ is, the larger is the metal depletion. This result should be extended to bigger PAHs. We conclude that organometallic chemistry can participate to the depletion of metals.We synthetized grains composed of small cristallized cores of metal (diameter from 20A to 200A) embedded in pyrene. The mean diameter of grains depends of the ratio pyrene/metal.Finally, we showed that organometallic reactions can be catalytic. Large organic molecules could be synthetized faster in the ISM through such this process than through classical collisions. We propose that the first ring of PAH molecules could be synthetised in this way.

Image Quality Control and Alignment of a Submillimeter Balloon-Borne Segmented Telescope

PRONAOS is a balloon-borne system dedicated to astronomical observations in the submillimeter range (180µm - 1050µm) based on the use of a 2m Cassegrain telescope. The primary mirror consists of six CFRP (Carbon Fiber Reinforced Plastic) panels, each being positioned by three actuators. The rotation angles of the panels have been measured in the visible range with the help of a CCD and digital centroiding techniques that were necessary because of the light scattering on the CFRP mirror. The translation movements (along the optical axis) of the panels have been measured with an interference technique in the submillimeter range. Both visible and submillimeter measurements were also necessary to determine the alignment of the telescope - focal instrument system with the star sensor. The whole alignment process leads to a precision of ±8″ for the rotation angles and ±7µm for the translation of each panel, sufficient for a qualification of the system.

French activity in infrared astronomy from stratospheric balloons

The setup and results of the experiment AROME to measure the 3.3 micron feature in diffuse galactic emission attributed to PAHs using stratospheric balloons are described. The main balloon project, Pronaus, consists of a 2 m telescope with two focal plane instruments: a submillimeter photometer dedicated to the measurement of very faint sources and a high resolution heterodyne spectrometer that measures water vapor and other species not observable from the ground.

Observation of the diffuse galactic emission at 6.2 μm

We present the observation of the 6.2 μm emission of the inner galactic disk obtained with the AROME balloon‐borne experiment. The galactic coordinates of the covered region are −5°≤1≤35° and ‖ b‖≤6°, with an angular resolution of 0.7°. The measurements reveal the existence of an emission feature at 6.2 μm all over this region. The averaged 6.2 μm surface brightness (‖ b ‖≤1°, 8°≤1≤35°) is λIλ=(1.2±0.3) 10−5 Wm−2 sr−1, with a continuum λ Iλ=(5.9±1.2) 10−6 Wm−2 sr−1 and a feature’s intensity Δλ Iλ=(6.1±1.3) 10−7 Wm−2 sr−1. We can compare this value to the 3.3 μm emission observed with AROME (Giard et al. 19881) and to the 12 μm (IRAS) surface brightness: the ratios are respectively Δλ Iλ (6.2/3.3)=9±2 (extinction corrected) and Δλ Iλ 6.2/λ Iλ12=0.09±0.02; these color ratios are similar to those obtained on UV excited nebulae, despite very different radiation field intensities. This supports the idea of a common origin for the near infrared radiation from excited nebulae and the diffuse interstellar medium:...

PRONAOS: a two-meter submillimeter telescope to observe the cold Universe from the stratosphere

Abstract PRONAOS is a French balloon-borne 2-meter submillimeter telescope for astronomy. Developed and operated from 1986 to 1999, it has been a precursor for the two European space missions to be launched in 2007: FIRST and Planck-Surveyor. PRONAOS has been built as a light and autonomous space platform able to resist the very hostile environment at the altitude of 40 kilometers. It has thus driven many technological developments such as a light carbon-fiber active optics, a daylight star sensor, a high-rate reliable telemetry, high sensitivity 300 mK bolometers and a pointing system with a 5 arcseconds accuracy. With three successful stratospheric flights the major scientific contributions of PRONAOS have been: (1) the first measurement of the positive part of the spectral distortion of the Cosmic Microwave Background toward a cluster of galaxies; (2) the discovery of a cold dust phase in the Galactic interstellar medium, with temperatures ranging from 12 to 15 K, and evidence for new dust emissivity properties.