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See detailLatitudinal structure of the Venus O2 infrared airglow: A signature of small-scale dynamical processes in the upper atmosphere
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Piccioni, Giuseppe et al

in Icarus (2014), 236

Images of the nightside limb of Venus have been obtained in the northern hemisphere with the VIRTIS multispectral infrared imager on board Venus Express between April 2006 and October 2008. We analyze the ... [more ▼]

Images of the nightside limb of Venus have been obtained in the northern hemisphere with the VIRTIS multispectral infrared imager on board Venus Express between April 2006 and October 2008. We analyze the latitudinal distribution of the O2(a1D) airglow limb profiles at 1.27 lm to characterize its distribution and variability. We show that the instantaneous structure of the emission is very different from the statistical global view of an enhanced emission near the equator, decreasing in brightness and slightly increasing in altitude toward the poles. The peak intensity of the limb profiles varies by a factor up to 50 between the brightest spots and the darkest regions. The bright airglow spots correspond to regions of enhanced downward flow of oxygen atoms originating from the dayside. Considerable variations in brightness and morphology are observed in the altitude–latitudinal distribution over a 24-h period. Analysis of the limb profiles indicates that secondary airglow peaks located at altitudes higher than the mean value of 96 km are observed on about 30% of the latitudinal cuts, but they are concentrated in narrow latitude areas extending over a few hundred kilometers. Most of them occur in transition regions between two altitude regimes in the 50 to 60 N region, possibly associated with the drop of the cloud top altitude observed equatorward of the ‘‘cold collar’’. We interpret these results as an indication that the strength of vertical transport in this mesosphere–thermosphere transition region is very variable both in location and time. This variability, also observed in nadir airglow images and wind measurements, is a key characteristic of the mesosphere–thermosphere transition region. It may be caused by fluctuations of the global day-to-night circulation generated by gravity waves. We show with a one dimensional model that local enhancements of eddy transport is a possibility. This variability is currently not accounted for by global circulation models that predict a single stable region of enhanced airglow in the vicinity of the antisolar point. [less ▲]

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See detailTime variations of O2(a1Delta) nightglow spots on the Venus nightside and dynamics of the upper mesosphere
Soret, Lauriane ULg; Gérard, Jean-Claude ULg; Piccioni, Giuseppe et al

in Icarus (2014), 237

The dynamical regime of the Venus upper atmosphere is mainly decomposed into three regions. The first one, located below 65 km of altitude is governed by the retrograde superrotational zonal (RSZ ... [more ▼]

The dynamical regime of the Venus upper atmosphere is mainly decomposed into three regions. The first one, located below 65 km of altitude is governed by the retrograde superrotational zonal (RSZ) circulation. The second region above 130 km is dominated by the subsolar to antisolar (SS–AS) circulation. The dynamics of the transition region in between are still not fully understood. However, the O2(a1D) nightglow emission at 1.27 lm, whose emitting layer is located at 96 km, can be used as a tracer of the dynamics in this transition region and the imaging spectrometer VIRTIS-M on board Venus Express, orbiting Venus since April 2006, acquired a large amount of nadir observations at this wavelength. Several previous studies showed that the O2(a1D) nightglow emission is statistically located near the antisolar point. In this study, individual VIRTIS-M nadir observations have been analyzed to investigate the variability of the phenomenon. Bright patches of 1.27 lm airglow have been extracted from every observation. It appears that the location of the bright patch is highly variable, even though the brightest patches occur near the antisolar point. Nadir observations have also been divided into time series, allowing generating animations to follow the intensity and the displacement of bright patches over time. Apparent wind velocities and characteristic decay/rise times and have been deduced from these time series. The speed of the displacements varies from 0 up to 213 m s 1, with a mean value of 54 m s 1. Owing to the high variability of the direction of the displacements both in the short and the long terms, no clear trend of a global motion at 96 km can be deduced from these observations. The mean decay time is 750 min while the mean rise time is 1550 min. The decay time can be explained as a combination of radiative decay and atomic oxygen transport. [less ▲]

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See detailOpen flux in Saturn's magnetosphere
Badman, Sarah; Jackman, Caitriuna; Nichols, Jonathan et al

in Icarus (2014), 231

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See detailThe tumbling spin state of (99942) Apophis
Pravec, P; Scheirich, P; Ďurech, J et al

in Icarus (2014), 233

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See detailHubble observations of Jupiter’s north–south conjugate ultraviolet aurora
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Radioti, Aikaterini ULg et al

in Icarus (2013), 226

Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a ... [more ▼]

Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a statistical basis or were not obtained with high sensitivity and resolution. Such observations are important to discriminate between different mechanisms responsible for the electron acceleration of the different components of the aurora such as the satellite footprints, the «main oval» or the polar emissions. The field of view of the ACS and STIS cameras on board HST is not wide enough to provide images of the full jovian disk. We thus compare the morphology of the north and south aurora observed 55 min apart and we point out similarities and differences. On one occasion HST pointed successively the two polar regions and auroral images were seen separated by only 3 min. This makes it possible to compare the emission structure and the emitted FUV power of corresponding regions. We find that most morphological features identified in one hemisphere have a conjugate counterpart in the other hemisphere. However, the power associated with conjugate regions of the main oval, diffuse or discrete equatoward emission observed quasi-simultaneously may be different in the two hemispheres. It is not directly nor inversely proportional to the strength of the B-field as one might expect for diffuse precipitation or field-aligned acceleration with equal ionospheric electron density in both hemispheres. Finally, the lack of symmetry of some polar emissions suggests that some of them could be located on open magnetic field lines. [less ▲]

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See detailComparative analysis of airglow emissions in terrestrial planets, observed with VIRTIS-M instruments on board Rosetta and Venus Express
Migliorini, A.; Piccioni, G.; Capaccioni, F. et al

in Icarus (2013), 226

Airglow emissions are optimal processes to investigate the chemistry and dynamics in planetary atmospheres. In this study, we focus on the O2 and OH airglow emissions in Venus, Earth, and Mars atmospheres ... [more ▼]

Airglow emissions are optimal processes to investigate the chemistry and dynamics in planetary atmospheres. In this study, we focus on the O2 and OH airglow emissions in Venus, Earth, and Mars atmospheres, which are controlled by chemical reactions common to the three planets. By studying these phenomena on Venus, Earth, and Mars using similar instruments, we are able to derive information about their photochemistry and the physical conditions of the atmospheres, but also to constrain the dynamics responsible for transport of atomic oxygen, ozone and other minor species. After a review of the nightglow emissions observed in the Venus atmosphere, we analyze the O2 and OH airglow emissions in the Earth's atmosphere observed during the 3 swing-bys of our planet by the Rosetta spacecraft. We also report the detection of the O2 nightglow emission in the Mars atmosphere, observed in February 2007 during the Rosetta fly-by of the planet. The airglow characteristics are in agreement with the measurements obtained from sensors on board Mars Express. [less ▲]

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See detailThe characteristics of the O2 Herzberg II and Chamberlain bands observed with VIRTIS/Venus Express
Migliorini, A.; Piccioni, G.; Gérard, Jean-Claude ULg et al

in Icarus (2013)

The oxygen Venus nightglow emissions in the visible spectral range have been known since the early observations from the Venera spacecraft. Recent observations with the VIRTIS instrument on board Venus ... [more ▼]

The oxygen Venus nightglow emissions in the visible spectral range have been known since the early observations from the Venera spacecraft. Recent observations with the VIRTIS instrument on board Venus Express allowed us to re-examine the Herzberg II system of O2 and to further study its vertical distribution, in particular the (0–m00 with m00 = 7–13) bands. The present work describes the vertical profile of the observed bands and relative intensities from limb observation data. The wavelength-integrated intensities of the Herzberg II bands, with m00 = 7–11, are inferred from the recorded spectra. The resulting values lie in the range of 84–116 kR at the altitudes of maximum intensity, which are found to lie in the range of 93–98 km. Three bands of the Chamberlain system, centered at 560 nm, 605 nm, and 657 nm have been identified as well. Their emission peak is located at about 100 km, 4 km higher than the Herzberg II bands. For the first time, the O2 nightglow emissions were investigated simultaneously in the visible and in the IR spectral range, showing a good agreement between the peak position for the Herzberg II and the O2ða1Dg—X3R g Þ bands. An airglow model, proposed by Gérard et al. (Gérard, J.C., Soret, L., Migliorini, A., Piccioni, G. [2012]. Icarus.) starting from realistic O and CO2 vertical distributions derived from Venus-Express observations, allows reproduction of the observed profiles for the three O2 systems. [less ▲]

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See detailOxygen nightglow emissions of Venus: Vertical distribution and collisional quenching
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Migliorini, Alessandra et al

in Icarus (2013)

We compare the altitude of three O2 night airglow emissions observed at the limb of Venus by the VIRTIS spectral imager with the values predicted by a model accounting for the different radiative ... [more ▼]

We compare the altitude of three O2 night airglow emissions observed at the limb of Venus by the VIRTIS spectral imager with the values predicted by a model accounting for the different radiative lifetimes and collisional deactivation of the upper O2 states. The O and CO2 density profiles are based on remote sensing observations from the Venus Express spacecraft. Effective production efficiencies of the involved O2 metastable states and quenching coefficients by oxygen and carbon dioxide are adjusted to provide the best match with the measured emission limb profiles. We find values in general good agreement with earlier studies for the c1Σ-u state which gives rise to the Herzberg II bands. In particular, we confirm the low net yield of the c state production and the importance of its deactivation by CO2, for which we derive a quenching coefficient of 3x10-16 cm-3 s-1. The ∼4.5 km higher altitude of the Chamberlain band emission also recently detected by VIRTIS and the ratio of the Herzberg II/Chamberlain bands observed with Venera are well reproduced. To reach agreement, we use a 12% yield for the A’3Δu production following O atom association and quenching coefficients by O and CO2 of 1.3x10-11 cm-3 s-1 and 4.5x10-13 cm-3 s-1 respectively. We conclude that the different peak altitudes of the IR Atmospheric, Herzberg II and the Chamberlain bands reflect the relative importance of radiative relaxation and collisional quenching by O and CO2. [less ▲]

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See detailRemote sensing of the energy of auroral electrons in Saturn’s atmosphere: Hubble and Cassini spectral observations
Gérard, Jean-Claude ULg; Gustin, Jacques ULg; Pryor, Wayne et al

in Icarus (2013), 223

Saturn’s north ultraviolet aurora has been successfully observed twice between March and May 2011 with the STIS long-slit spectrograph on board the Hubble Space Telescope. Spatially resolved spectra at ... [more ▼]

Saturn’s north ultraviolet aurora has been successfully observed twice between March and May 2011 with the STIS long-slit spectrograph on board the Hubble Space Telescope. Spatially resolved spectra at ∼12 Å spectral resolution have been collected at different local times from dawn to dusk to determine the amount of hydrocarbon absorption. For this purpose, the HST telescope slewed across the auroral oval from mid-latitudes up to beyond the limb while collecting spectral data in the timetag mode. Spectral images of the north ultraviolet aurora were obtained within minutes and hours with the UVIS spectrograph on board Cassini. Several daytime sectors and one nightside location were observed and showed signatures of weak absorption by methane present in (or above) the layer of the auroral emission. No absorption from other hydrocarbons (e.g. C2H2) has been detected. For the absorbed spectra, the overlying slant CH4 column varies from 3x1015 to 2x1016 cm-2, but no clear dependence on local time is identified. A Monte Carlo electron transport model is used to calculate the vertical distribution of the H2 emission and to relate the observed spectra to the energy of the primary auroral electrons. Assuming electron precipitation with a Maxwellian energy distribution into a standard model atmosphere, we find that the mean energy ranges from less than 3 to ∼10 keV. These results are compared with previous determinations of the energy of Saturn’s aurora based on ultraviolet spectra and limb images. We conclude that the energies derived from spectral methods indicate a wide range of electron energies while the nightside limb images suggest that the auroral precipitation is consistently soft. We emphasize the need for more realistic model atmospheres with temperature and hydrocarbon distributions appropriate to high-latitude conditions. [less ▲]

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See detailVenus nitric oxide nightglow mapping from SPICAV nadir observations.
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Dumont, Maïté ULg et al

in Icarus (2013)

Nitric oxide δ (190-240 nm) and γ (255-270 nm) emissions on the Venus nightside have been observed with Venus Express SPICAV instrument operated in the nadir mode. These ultraviolet emissions arise from ... [more ▼]

Nitric oxide δ (190-240 nm) and γ (255-270 nm) emissions on the Venus nightside have been observed with Venus Express SPICAV instrument operated in the nadir mode. These ultraviolet emissions arise from the desexcitation of excited NO molecules created by radiative recombination of O(3P) and N(4S) atoms. These atoms are produced on the dayside of the planet through photodissociation of CO2 and N2 molecules and are transported to the nightside by the global subsolar to antisolar circulation. We analyze a wide dataset of nadir observations obtained since 2006 to determine the statistical distribution of the NO nightglow and its variability. Individual observations show a great deal of variability and may exhibit multiple maxima along latitudinal cuts. We compare this global map with the results obtained during the Pioneer-Venus mission and with the recent O2(a1Δg) nightglow map. The NO airglow distribution shows a statistical bright region extending from 01:00 and 03:30 local time and 25°N to 10°S, very similar to the Pioneer result obtained 35 years earlier during maximum solar activity conditions. The shift from the antisolar point and the difference with the O2 airglow indicate that superrotating zonal winds are statistically weak near 97 km, but play an important role in the lower thermosphere. We compare these results with other evidence for superrotation in the thermosphere and point out possible sources of momentum transfer. [less ▲]

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See detailThe vertical distribution of the Venus NO nightglow: limb profiles inversion and one-dimensional modeling
Stiepen, Arnaud ULg; Soret, Lauriane ULg; Gérard, Jean-Claude ULg et al

in Icarus (2012), 220

Ultraviolet (UV) spectra of the δ (190-240 nm) and γ (225-270 nm) bands of the nitric oxide (NO) molecule have been measured on the nightside of the atmosphere of Venus with the Spectroscopy for ... [more ▼]

Ultraviolet (UV) spectra of the δ (190-240 nm) and γ (225-270 nm) bands of the nitric oxide (NO) molecule have been measured on the nightside of the atmosphere of Venus with the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument on board Venus Express (VEX). Excited NO molecules on the nightside of the planet are created by radiative recombination of O(3P) and N(4S) atoms. The atoms are produced by photodissociation of CO2 and N2 molecules on the dayside and then transported on the nightside by the global circulation. We analyze all nightside limb profiles obtained since 2006 and provide a statistical study of the nitric oxide airglow layer and its variability. We also apply a spatial deconvolution and an Abel inversion method to the limb profiles to retrieve and quantify the volume emission rate distribution and its dependence on several factors. We also show that about 10% of the limb profiles exhibits a secondary peak located above or below the main airglow peak. Furthermore, a one-dimensional chemical-diffusive model is used to simultaneously model the globally averaged NO and O2(a1Δg) airglow vertical distributions using CO2 and O density profiles rooted in VIRTIS and SPICAV observations. We find that a downward flux of 2×10 9 N(4S) atoms cm−2s−1 and a eddy diffusion coefficient equal to 1 x10 11/sqrt(n) cm−2s−1, where n is the total number density, provide the best set of values to parametrize the one-dimensional representation of the complex 3-D dynamical processes. [less ▲]

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See detailThe remarkable surface homogeneity of the Dawn mission target (1) Ceres
Carry, Benoît; Vernazza, Pierre; Dumas, Christophe et al

in Icarus (2012), 217

Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron ... [more ▼]

Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron spectroscopy. While Ceres' visible and near-infrared disk-integrated spectra have been well characterized, little has been done about quantifying spectral variations over the surface. Any spectral variation would give us insights on the geographical variation of the composition and/or the surface age. The only work so far was that of Rivkin and Volquardsen ([2010], Icarus 206, 327) who reported rotationally-resolved spectroscopic (disk-integrated) observations in the 2.2-4.0 μm range; their observations showed evidence for a relatively uniform surface.Here, we report disk-resolved observations of Ceres with SINFONI (ESO VLT) in the 1.17-1.32 μm and 1.45-2.35 μm wavelength ranges. The observations were made under excellent seeing conditions (0.6″), allowing us to reach a spatial resolution of ˜75 km on Ceres' surface. We do not find any spectral variation above a 3% level, suggesting a homogeneous surface at our spatial resolution. Slight variations (about 2%) of the spectral slope are detected, geographically correlated with the albedo markings reported from the analysis of the HST and Keck disk-resolved images of Ceres (Li et al. [2006], Icarus 182, 143; Carry et al. [2008], Astron. Astrophys. 478, 235). Given the lack of constraints on the surface composition of Ceres, however, we cannot assert the causes of these variations. [less ▲]

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See detailSpatial correlation of OH Meinel and O2 Infrared Atmospheric nightglow emissions observed with VIRTIS-M on board Venus Express
Gérard, Jean-Claude ULg; Soret, Lauriane ULg; Piccioni, G. et al

in Icarus (2012)

We present the two-dimensional distribution of the O2 a1∆-X3Σ (0-0) band at 1.27 µm and the OH ∆v=1 Meinel airglow measured simultaneously with the Visible and Infrared Thermal Imaging Spectrometer ... [more ▼]

We present the two-dimensional distribution of the O2 a1∆-X3Σ (0-0) band at 1.27 µm and the OH ∆v=1 Meinel airglow measured simultaneously with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express. We show that the two emissions present very similar spatial structures. A cross-correlation analysis indicates that the highest level of correlation is reached with only very small relative shifts of the pairs of images. In spite of the strong spatial correlation between the morphology of the bright spots in the two emissions, we also show that their relative intensity is not constant, in agreement with earlier statistical studies of their limb profiles. We conclude that the two emissions have a common precursor that controls the production of both excited species. We argue that atomic oxygen, which produces O2(1∆) molecules by three-body recombination and is the precursor of ozone formation, also governs to a large extent the OH airglow morphology through the H + O3 → OH* + O2 reaction. [less ▲]

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See detailCassini-UVIS observation of dayglow FUV emissions of carbon in the thermosphere of Venus
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Gustin, Jacques ULg et al

in Icarus (2012), 220

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. The intensities of the ultraviolet multiplets of carbon at 126.1 ... [more ▼]

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. The intensities of the ultraviolet multiplets of carbon at 126.1, 156.1 and 165.7 nm are determined using a least squares fit technique applied to all dayglow spectra recorded by UVIS along the Cassini track. These intensities are compared with the results of a full radiative transfer model of these emissions, that includes the known photochemical sources of photons and resonant scattering of sunlight. The carbon density profile of the Venus thermosphere has never been directly measured and is taken from a model. We find a serious disagreement between these observations and modeling that can be accounted for by applying a scaling factor to the carbon column. This needed scaling factor is found to increase monotonically with solar zenith angle, suggesting a possible photochemical origin to the disagreement, possibly involving the photochemistry of molecular oxygen to which the carbon density is highly sensitive. [less ▲]

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See detailUVIS observations of the FUV OI and CO 4P Venus dayglow during the Cassini flyby
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Gustin, Jacques ULg et al

in Icarus (2010), 207

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of ... [more ▼]

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of the OI emissions at 130.4 and OI 135.6 nm, and of the bands of the CO fourth positive system which are dominated by fluorescence scattering. We compare the brightness observed along the UVIS foot track of the two OI multiplets with that deduced from a model of the excitation of these emissions by photoelectron impact on O atoms and resonance scattering of the solar 130.4 nm emission. The large optical thickness 130.4 nm emission is accounted for using a radiative transfer model. The airglow intensities are calculated along the foot track and found to agree with the observed 130.4 nm brightness within ˜10%. The modeled OI 135.6 nm brightness is also well reproduced by the model. The oxygen density profile of the VTS3 model is found to be consistent with the observations. We find that self-absorption of the (0, v″) bands of the fourth positive emission of CO is important and we derive a CO vertical column of about 6.4 × 10[SUP]15[/SUP] cm[SUP]‑2[/SUP] in close agreement with the value provided by the VTS3 empirical atmospheric model. [less ▲]

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See detailAtomic oxygen distribution in the Venus mesosphere from observations of O[SUB]2[/SUB] infrared airglow by VIRTIS-Venus Express
Gérard, Jean-Claude ULg; Saglam, Adem ULg; Piccioni, Giuseppe et al

in Icarus (2009), 199

This VIRTIS instrument on board Venus Express has collected spectrally resolved images of the Venus nightside limb that show the presence of the (0,0) band of the Deltag1-->Sigmag3 infrared atmospheric ... [more ▼]

This VIRTIS instrument on board Venus Express has collected spectrally resolved images of the Venus nightside limb that show the presence of the (0,0) band of the Deltag1-->Sigmag3 infrared atmospheric system of O[SUB]2[/SUB] at 1.27 mum. The emission is produced by three-body recombination of oxygen atoms created by photodissociation of CO[SUB]2[/SUB] on the dayside. It is consistently bright so that emission limb profiles can be extracted from the images. The vertical distribution of O[SUB]2[/SUB](Deltag1) may be derived following Abel inversion of the radiance limb profiles. Assuming photochemical equilibrium, it is combined with the CO[SUB]2[/SUB] vertical distribution to determine the atomic oxygen density. The uncertainties on the O density caused by the Abel inversion reach a few percent at the peak, increasing to about 50% near 120 km. We first analyze a case when the CO[SUB]2[/SUB] density was derived from a stellar occultation observed with the SPICAV spectrometer simultaneously with an image of the O[SUB]2[/SUB] limb airglow. In other cases, an average CO[SUB]2[/SUB] profile deduced from a series of ultraviolet stellar occultations is used to derive the O profile, leading to uncertainties on the O density less than 30%. It is found that the maximum O density is generally located between 94 and 115 km with a mean value of 104 km. It ranges from less than 1×10[SUP][/SUP] to about 5×10[SUP][/SUP] cm[SUP][/SUP] with a global mean of 2.2×10[SUP][/SUP] cm[SUP][/SUP]. These values are in reasonable agreement with the VIRA midnight oxygen profile. The vertical O distribution is generally in good agreement with the oxygen profile calculated with a one-dimensional chemical-diffusive model. No statistical latitudinal dependence of the altitude of the oxygen peak is observed, but the maximum O density tends to decrease with increasing northern latitudes. The latitudinal distribution at a given time exhibits large variations in the O density profile and its vertical structure. The vertical oxygen distribution frequently shows multiple peaks possibly caused by waves or variations in the structure of turbulent transport. It is concluded that the O[SUB]2[/SUB] infrared night airglow is a powerful tool to map the distribution of atomic oxygen in the mesosphere between 90 and 115 km and improve future Venus reference atmosphere models. [less ▲]

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See detailNuclear spin temperature of ammonia in Comet 9P/Tempel 1 before and after the Deep Impact event
Kawakita, Hideyo; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Icarus (2007), 187

The Deep Impact mission succeeded in excavating inner materials from the nucleus of Comet 9P/Tempel 1 on 2005 July 04 (at 05:52 UT). Comet 9P/Tempel 1 is one of Jupiter family short period comets, which ... [more ▼]

The Deep Impact mission succeeded in excavating inner materials from the nucleus of Comet 9P/Tempel 1 on 2005 July 04 (at 05:52 UT). Comet 9P/Tempel 1 is one of Jupiter family short period comets, which might originate in the Kuiper belt region in the solar nebula. In order to characterize the comet and to support the mission from the ground-based observatory, optical high-dispersion spectroscopic observations were carried out with the echelle spectrograph (UVES) mounted on the 8-m telescope VLT (UT2) before and after the Deep Impact event. Ortho-to-para abundance ratios (OPRs) of cometary ammonia were determined from the NH[SUB]2[/SUB] emission spectra. The OPRs of ammonia on July 3.996 UT and 4.997 UT were derived to be 1.28±0.07 (nuclear spin temperature: T[SUB][/SUB]=24±2 K) and 1.26±0.08 (T[SUB][/SUB]=25±2 K), respectively. There is no significant change between before and after the impact. Actually, most materials ejected from the impact site could have moved away from the nucleus on July 4.997 UT, about 17 h after the impact. However, a small fraction of the ejected materials might remain in the slit of UVES instrument at that time because an excess of about 20% in the NH[SUB]2[/SUB] emission flux is observed above the normal activity level was found [Manfroid, J., Hutsemékers, D., Jehin, E., Cochran, A.L., Arpigny, C., Jackson, W.M., Meech, K.J., Schulz, R., Zucconi, J.-M., 2007. Icarus. This issue]. If the excess of NH[SUB]2[/SUB] on July 04.997 UT was produced from icy materials excavated by the Deep Impact, then an upper-limit of the ammonia OPR would be 1.75 (T[SUB][/SUB]>17 K) for those materials. On the other hand, the OPR of ammonia produced from the quiescent sources was similar to that of the Oort cloud comets observed so far. This fact may imply that physical conditions where cometary ices formed were similar between Comet 9P/Tempel 1 and the Oort cloud comets. [less ▲]

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See detailThe Cassini Campaign observations of the Jupiter aurora by the Ultraviolet Imaging Spectrograph and the Space Telescope Imaging Spectrograph
Ajello, Joseph M.; Pryor, Wayne; Esposito, Larry et al

in Icarus (2005), 178(2), 327-345

We have analyzed the Cassini Ultraviolet Imaging, Spectrometer (UVIS) observations of the Jupiter aurora with an auroral atmosphere two-stream electron transport code. The observations Of Jupiter by UVIS ... [more ▼]

We have analyzed the Cassini Ultraviolet Imaging, Spectrometer (UVIS) observations of the Jupiter aurora with an auroral atmosphere two-stream electron transport code. The observations Of Jupiter by UVIS took place during the Cassini Campaign. The Cassini Campaign included Support spectral and imaging observations by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS). A major result for the UVIS observations was the identification of a large color variation between the far ultraviolet (FUV: 1100-1700 angstrom) and extreme ultraviolet (EUV: 800-1100 angstrom) spectral regions. This change probably occurs because of a large variation in the ratio of the soft electron flux (10-3000 eV) responsible for the EUV aurora to the hard electron flux (similar to 15-22 keV) responsible for the FUV aurora. On the basis of this result a new color ratio for integrated intensities for EUV and FUV was defined (4 pi I1550-1620 angstrom/4 pi I (1030-1150 angstrom)) which varied by approximately a factor of 6. The FUV color ratio (4 pi I (1550-1620) angstrom/4 pi (1230-1300) (angstrom)) was note stable with a variation of less than 50% for the observations studied. The medium resolution (0.9 angstrom FWHM, G140M grating) FUV observations (1295-1345 angstrom and 1495-1540 angstrom) by STIS on 13 January 2001, on the other hand, were analyzed by a spectral modeling technique using a recently developed high-spectral resolution model for the electron-excited H-2 rotational lines. The STIS FUV data were analyzed with a model that considered the Lyman band spectrum (B (1) Sigma(u)(+) -> X-1 Sigma(g)(+)) as composed of an allowed direct excitation component (X-1 Sigma(g)(+) B-1 (+)(Sigma u)) and an optically forbidden component (X-1 Sigma(g)(+) -> EF, GK, H (H) over bar,.... (1)Sigma(u)(+) followed by the cascade transition (1)Sigma -> B-1 Sigma(u)(+)). The medium-resolution spectral regions for the Jupiter aurora were carefully chosen to emphasize the cascade component. The ratio of the two components is a direct measurement of the mean secondary electron energy of the aurora. The mean secondary electron energy of the aurora varies between 50 and 200 eV for the polar cap, limb and auroral oval observations. We examine a long time base of Galileo Ultraviolet Spectrometer color ratios from the standard mission (1996-1998) and compare them to Cassini UVIS, HST, and International Ultraviolet Explorer (IUE) observations. (c) 2005 Elsevier Inc. All rights reserved. [less ▲]

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See detailAsteroid 45 Eugenia - Lightcurves and the pole orientation
Taylor, R. C.; Birch, P. V.; Pospieszalska-Surdej, Anna ULg et al

in ICARUS (1988), 73

Nine lightcurves of asteroid 45 Eugenia, three from 1969 and six from 1984, are given. In 1984 - 1985 the H[SUB]0[/SUB] magnitude of Eugenia, corrected to the lightcurve maximum, was 7.47 and the slope ... [more ▼]

Nine lightcurves of asteroid 45 Eugenia, three from 1969 and six from 1984, are given. In 1984 - 1985 the H[SUB]0[/SUB] magnitude of Eugenia, corrected to the lightcurve maximum, was 7.47 and the slope parameter G[SUB]0[/SUB] was 0.04. The north pole of Eugenia is within ±10° of ecliptic longitude 106° and latitude +26° (or 295° and +34°). This solution is consistent with an amplitude-aspect pole analysis. The sideral period is 0.2374645±0.0000002 day and the sense of rotation is retrograde. [less ▲]

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See detailAsteroid 532 Herculina - Lightcurves, pole orientation and a model
Taylor, R. C.; Birch, P. V.; Drummond, J. et al

in Icarus (1987), 69

Photoelectric lightcurves of 532 Herculina in 1984 show two maxima and two minima with a synodic rotation period of 0.39185±0.00002 day (1sigma). During some other oppositions the Herculina lightcurve has ... [more ▼]

Photoelectric lightcurves of 532 Herculina in 1984 show two maxima and two minima with a synodic rotation period of 0.39185±0.00002 day (1sigma). During some other oppositions the Herculina lightcurve has only one maximum and one minimum over that same rotation period. The absolute magnitude in V is 6.13±0.02 mag, the phase coefficient in V is 0.037±0.002, and the mean colors are B-V = +0.86±0.04 and U-B = +0.43±0.02. The authors applied photometric astrometry and the results indicate a sidereal period of 0.3918711±0.0000001 day with retrograde rotation for a north pole at 276° long and +1° lat. The uncertainty of the pole is ±1°. A model of Herculina is presented that generates lightcurves consistent with both the observed amplitudes and the timings of extrema over precisely 28,630 sidereal rotations during 30 years. [less ▲]

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