Publication archive

Publication archive

We investigated electron dissociative recombination of N+2 ions, electron impact dissociation of N2 molecules, nonthermal exothermic ionosphere-related photochemical reactions, atmospheric sputtering via solar wind and magnetospheric particles, solar wind pick-up and the loss of 14N to 14C via cosmic rays as possible sources of nitrogen isotope fractionation in Titan's atmosphere where this molecule is the principal constituent.
Published: 02 April 2000
Published: 02 May 2000
The recent passage of the Hale-Bopp (C/1995 O1) comet has provided the first opportunity to analyse the infrared spectral properties of a bright comet both from the ground and by the ISO space observatory. Previous works have already been dedicated to study the potential candidates to reproduce the cometary feature at 10 micron observed for different comets. We have applied a similar approach to compare the Hale-Bopp (C/1995 O1) spectra with laboratory data. The best fit has been obtained by using a mixture of crystalline Mg-rich olivine (forsterite), amorphous olivine and amorphous carbon grains. Some constraints on the possible cometary grain types derive from our simulation. Aggregates of submicron particles, composed of amorphous and crystalline olivine and amorphous carbon materials seem to be compatible with the cometary emission. Moreover, the possibility of fitting observational data on a wide IR spectra range, offered by ISO, provides interesting hints about the size distribution of grains responsible for the detected features
Published: 06 December 1998
I compute speed of sound profiles for the four giant planets using simple atmosphere models, and explore the effect on the profiles of ortho : para hydrogen conversion, and the drop in mixing ratio of condensible species at the tropopause.
Published: 01 December 1998
III. First Modeling of a CO-Dominated Coma, with Application to Comets 46 P/Wirtanen and 29 P/Schwassmann-Wachmann I

We present the first gasdynamic simulations of the coma formed by the diffusion from a comet nucleus interior of a volatile molecule at large heliocentic distance. The method used is a generalization of that described in J. F. Crifo et al. (1995, Icarus 116, 77-112). The molecule is assumed to be CO.

Published: 01 March 1999
The laboratory investigation of the atmospheric photochemistry of planets and satellites is mainly carried out in static systems. These studies are often poor models of chemical processes in atmospheres because: (1) much higher mixing ratios of minor constituents must be used to accurately determine the amount of reactant consumed and to obtain sufficient products for analysis, (2) secondary photolysis of the initial photoproducts often occurs, (3) wall reactions occur, and (4) most of the starting material is converted to products to obtain enough for spectroscopic analysis. The use of a photochemical flow reactor either circumvents or minimizes these problems by using gas mixtures and photolysis conditions more representative of a planetary atmosphere. A gas mixture, composed of a small amount of a reactant gas diluted in a much larger amount of carrier gas, is flowed past a UV lamp for an extended period of time. Unconsumed reactants and products are collected in traps downstream until amounts sufficient for spectral analysis are collected. FTIR and NMR analysis provides structural information and quantitative data on their rates of formation.
Published: 02 August 2000
Imaging of comet 46P/Wirtanen was performed in the standard VRI filters on 10 and 11 November 1996 with the 1.0 m telescope of the South African Astronomical Observatory (SAAO). After proper processing and calibration, the images have been used to derive information about the isophote distribution, magnitude and colour indices. We observed a coma extending to at most ~5×10³ km. We derive absolute magnitudes of the coma for the different filters and the colours V-R = 0.18±0.17 and R-I = 0.39±0.16.
Published: 06 December 1998
Published: 02 April 2000
Recent observations with the Wide-Field Planetary Camera (WFPC-2) on the Hubble Space Telescope (HST) show an unexpectedly rapid change in the atmospheric albedo contrast between the north and south hemispheres. In 1994 at blue wavelengths, the north was around 15% brighter than the south, and was expected to fall to about 12% in 1997, but has dropped to only 6% brighter.
Published: 01 December 1999
From diffraction-limited images produced by the near-IR camera NICMOS aboard the Hubble Space Telescope we derived maps of Titan's surface in the methane windows near 1.1, 1.6, and 2.0 micron. Each part of Titan's atmosphere and surface was imaged at least twice over a time period of 24 h to look for moving clouds.
Published: 02 May 2000
Eds. Schmidt, R. and Guyenne, T.D.
Published: 02 May 1988
Workshop held 22-25 June 1999 in Paris, France.
Published: 02 August 1999
Proc. Kanzelhoehe Summer School, eds. A. Hanslmeier and M. Messerotti, Kluwer, 2001
Published: 02 June 2000
Kosovichev, A.G., Duvall, T.L. (eds.)
Published: 01 March 2000
The spectrometer on INTEGRAL (SPI) is one of the two main telescopes of the future INTEGRAL observatory. SPI is made of a compact hexagonal matrix of 19 high-purity germanium detectors shielded by a massive anticoincidence system. A HURA type coded aperture modulates the astrophysical signal. The spectrometer system, its physical characteristics and performances are presented. The instrument properties such as imaging capability, energy resolution and sensitivity have been evaluated by means of extensive Monte-Carlo simulations. With the expected performances of SPI, it will be possible to explore the gamma-ray sky in greater depth and detail than it was possible with previous gamma-ray telescopes like SIGMA, OSSE and COMPTEL. In particular, the high-energy resolution will allow for the first time the measurement of gamma-ray line profiles. Such lines are emitted by the debris of nucleosynthesis and annihilation processes in our Galaxy. Lines from these processes have already been measured, but due to the relatively poor energy resolution, details of the emission processes in the source regions could not be studied. With the high-resolution spectroscopy of SPI such detailed investigations will be possible.
Published: 17 September 1999
11-Aug-2020 04:32 UT

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