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See detailDiurnal thermosphere scale height from MEX/SPICAM grazing limb data
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S et al

Conference (2014, July 01)

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See detailVenus night side measurements of winds at 115 km altitude from NO bright patches tracking.
Bertaux, J.-L.; Gérard, Jean-Claude ULg; Stiepen, Arnaud ULg et al

Conference (2013, June)

N and O atoms produced by photo-dissociation of CO2 and N2 on the day side of Venus are transported to the night side in the thermospheric circulation. When the air parcel is descending, the recombination ... [more ▼]

N and O atoms produced by photo-dissociation of CO2 and N2 on the day side of Venus are transported to the night side in the thermospheric circulation. When the air parcel is descending, the recombination N+O→ NO produces the famous γ and δ bands of NO emission. Pioneer Venus (1978) suggested that the statistical center of the emission is off from the anti-solar point, about one- two hours in Local time after midnight. This is confirmed from SPICAV/VEX results, and the explanation generally accepted is the influence of retrograde super rotation. However, the emission takes place at 115 km, while VIRTIS/VEX, with maps of O2 emission (peak altitude 95 km) in the night side of Venus (recombination of O+O coming from the day side), has shown that the maximum of emission is statistically centered on the antisolar point. Therefore, there is no influence of super-rotation at 95 km. One way to explain this paradox is that the cause of the super rotation is different at 115 km and in the lower atmosphere. Alternately, some gravity waves could propagate from below, crossing the altitude 95 km with minimal interaction, and breaking around 115, depositing their momentum. Another consideration is that the altitude of N2 photo-dissociation is higher in the thermosphere than CO2, therefore the thermospheric circulation pattern may be different for the transport of N atoms, and O atoms. We have started building maps of the NO emission by moving around the spacecraft along its orbit on the night side. The idea is that NO emission is concentrated generally in rather well defined patches of light. Therefore, by comparing maps taken at 1 hour or 24 hr interval, we can make a “bright patch tracking”, and derive directly the velocity of the moving air parcel containing N and O (we are aware that a part of the motion could be due to a phase shift of a gravity wave, if it has some influence on the NO emission). Preliminary results from this exercise with Venus Express will be presented and discussed. [less ▲]

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See detailThe HARPS search for southern extra-solar planets: XXXI. The M-dwarf sample
Bonfils, X.; Delfosse, X.; Udry, S. et al

in Astronomy and Astrophysics (2013), 549

(Abridged) Searching for planets around stars with different masses probes the outcome of planetary formation for different initial conditions. This drives observations of a sample of 102 southern nearby ... [more ▼]

(Abridged) Searching for planets around stars with different masses probes the outcome of planetary formation for different initial conditions. This drives observations of a sample of 102 southern nearby M dwarfs, using a fraction of our guaranteed time on the ESO/HARPS spectrograph (Feb. 11th, 2003 to Apr. 1st 2009). This paper makes available the sample's time series, presents their precision and variability. We apply systematic searches and diagnostics to discriminate whether the observed Doppler shifts are caused by stellar surface inhomogeneities or by the radial pull of orbiting planets. We recover the planetary signals corresponding to 9 planets already announced by our group (Gl176b, Gl581b, c, d & e, Gl674b, Gl433b, Gl 667Cb and c). We present radial velocities that confirm GJ 849 hosts a Jupiter-mass planet, plus a long-term radial-velocity variation. We also present RVs that precise the planetary mass and period of Gl 832b. We detect long-term RV changes for Gl 367, Gl 680 and Gl 880 betraying yet unknown long-period companions. We identify candidate signals in the radial-velocity time series and demonstrate they are most probably caused by stellar surface inhomogeneities. Finally, we derive a first estimate of the occurrence of M-dwarf planets as a function of their minimum mass and orbital period. In particular, we find that giant planets (m sin i = 100-1,000 Mearth) have a low frequency (e.g. f<1% for P=1-10 d and f=0.02^{+0.03}_{-0.01} for P=10-100 d), whereas super-Earths (m sin i = 1-10 Mearth) are likely very abundant (f=0.36^{+0.25}_{-0.10} for P=1-10 d and f=0.35^{+0.45}_{-0.11} for P=10-100 d). We also obtained eta_earth=0.41^{+0.54}_{-0.13}, the frequency of habitable planets orbiting M dwarfs (1<m sin i<10 Mearth). For the first time, eta_earth is a direct measure and not a number extrapolated from the statistic of more massive and/or shorter-period planets. [less ▲]

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See detailSPICAM dayglow measurements: a tool to retrieve CO2 vertical density profile and exospheric temperatures
Stiepen, Arnaud ULg; Gérard, Jean-Claude ULg; Bougher, S. et al

Conference (2012, September)

We analyze the behavior of the CO2+ and CO Cameron ultraviolet dayglow in the atmosphere of Mars through a large dataset of dayside grazing limb observations performed by the Spectroscopy for ... [more ▼]

We analyze the behavior of the CO2+ and CO Cameron ultraviolet dayglow in the atmosphere of Mars through a large dataset of dayside grazing limb observations performed by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) on board the Mars Express spacecraft. Limb profiles are studied to retrieve the temperature of the Martian exosphere and its variability with season, latitude and solar activity. We use a one-dimensional chemical-diffusive model to retrieve the main features of the emissions and constrain the temperature and density vertical profiles of the main components of the Martian atmosphere. [less ▲]

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See detailA layer of ozone detected in the nightside upper atmosphere of Venus
Montmessin, Franck; Bertaux, J.-L.; Lefèvre, F. et al

in Icarus: International Journal of Solar System Studies (2011)

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See detailDiscovery and characterization of an ozone layer in Venus’atmosphere
Montmessin, F.; Bertaux, J.-L.; Lefèvre, F. et al

Conference (2011)

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See detailThe NO Venus nightglow: SPICAV observations and implications on transport in the lower thermosphere
Gérard, Jean-Claude ULg; Cox, Cédric ULg; Bertaux, J.-L.

Conference (2010, June 22)

A new set of 725 NO limb profiles has been analyzed. The profiles have been deconvolved and inverted to get volume emission rates. Updates mean VER peak altitude is 115 km, in excellent agreement with PV ... [more ▼]

A new set of 725 NO limb profiles has been analyzed. The profiles have been deconvolved and inverted to get volume emission rates. Updates mean VER peak altitude is 115 km, in excellent agreement with PV results obtained 30 years ago. The corresponding average vertical intensity is 1.2 kR. The altitude of emission occurs at a higher altitude near the bright spot region than at larger distances (by about 7 km). The location of the statistical bright spot is the same as observed with PV (that is shifted dawnward by 2 hrs and slightly south of AS point). The nightside mean vertical intensity is between 0.4 and 1.8 kR, which brackets the values derived from the limb profiles. These results, coupled with other airglow measurements, provide constraints on global atmospheric circulation and vertical transport [less ▲]

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See detailMars ultraviolet dayglow variability: SPICAM observations and comparison with airglow model
Cox, Cédric ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Journal of Geophysical Research. Planets (2010), 115

Dayglow ultraviolet emissions of the CO Cameron bands and the CO[SUB]2[/SUB][SUP]+[/SUP] doublet in the Martian atmosphere have been observed with the Spectroscopy for Investigation of Characteristics of ... [more ▼]

Dayglow ultraviolet emissions of the CO Cameron bands and the CO[SUB]2[/SUB][SUP]+[/SUP] doublet in the Martian atmosphere have been observed with the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars on board the Mars Express spacecraft. A large amount of limb profiles has been obtained which makes it possible to analyze variability of the brightness as well as of the altitude of the emission peak. Focusing on one specific season (Ls = [90,180] °), we find that the average CO peak brightness is equal to 118 ± 33 kR, with an average peak altitude of 121.1 ± 6.5 km. Similarly, the CO[SUB]2[/SUB][SUP]+[/SUP] emission shows a mean brightness of 21.6 ± 7.2 kR with a peak located at 119.1 ± 7.0 km. We show that the brightness intensity of the airglows is mainly controlled by the solar zenith angle and by solar activity. Moreover, during Martian summer of year 2005, an increase of the airglow peak altitude has been observed between Ls = 120° and 180°. We demonstrate that this variation is due to a change in the thermospheric local CO[SUB]2[/SUB] density, in agreement with observations performed by stellar occultation. Using a Monte Carlo one-dimensional model, we also show that the main features of the emission profiles can be reproduced for the considered set of data. However, we find it necessary to scale the calculated intensities by a fixed factor. [less ▲]

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See detailThe Mars ultraviolet dayglow variability: SPICAM observations and model comparison
Gérard, Jean-Claude ULg; Cox, Cédric ULg; Bougher, S. W. et al

Conference (2009, September 16)

Limb profiles of the CO Cameron and CO2+ doublet airglow have been observed over different conditions (latitude, season, SZA, F10.7). They have been individually modelled using currently accepted cross ... [more ▼]

Limb profiles of the CO Cameron and CO2+ doublet airglow have been observed over different conditions (latitude, season, SZA, F10.7). They have been individually modelled using currently accepted cross sections, and outputs from the MTGCM. They have been shown to co-vary, with a ICO/ICO2+ ratio of about 4.7, less than the modelled ratio.The peak brightness varies linearly with the F10.7 solar flux proxy, in a way compatible with the Mariner 6 and 7 observations. The intensity of both emissions is overestimated by the model (but large uncertainties exist in excitation cross sections). An increase of the altitude of both emissions has been observed during the 2005 summer season. It is a consequence of the dust load, followed by an increased thermospheric CO2 density observed with SPICAV during the same period. This density enhancement is partly predicted by GCM models. [less ▲]

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See detailConcurrent observations of the ultraviolet nitric oxide and infrared O[SUB]2[/SUB] nightglow emissions with Venus Express
Gérard, Jean-Claude ULg; Cox, Cédric ULg; Soret, Lauriane ULg et al

in Journal of Geophysical Research. Planets (2009), 114

Two prominent features of the Venus nightside airglow are the nitric oxide delta and gamma bands produced by radiative association of O and N atoms in the lower thermosphere and the O[SUB]2[/SUB] infrared ... [more ▼]

Two prominent features of the Venus nightside airglow are the nitric oxide delta and gamma bands produced by radiative association of O and N atoms in the lower thermosphere and the O[SUB]2[/SUB] infrared emission generated by three-body recombination of oxygen atoms in the upper mesosphere. The O[SUB]2[/SUB] airglow has been observed from the ground, during the Cassini flyby, and with VIRTIS on board Venus Express. It now appears that the global structure of the two emissions shows some similarities, but the statistical location of the region of strongest emission is not coincident. The Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) ultraviolet spectrograph has collected a large number of spectra of the Venus nitric oxide nightside airglow. Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) images have been obtained at the limb and in the nadir-viewing mode and have provided new information on the horizontal and vertical distribution of the emission. We present the first concurrent observations of the two emissions observed with Venus Express. We show that nadir observations generally indicate a low degree of correlation between the two emissions observed quasi-simultaneously at a common location. A statistical study of limb profiles indicates that the altitude and the brightness of the two airglow layers generally do not covary. We suggest that this lack of correlation is explained by the presence of strong horizontal winds in the mesosphere-thermosphere transition region. They carry the downflowing atoms over large distances in such a way that regions of enhanced NO emission generally do not coincide with zones of bright O[SUB]2[/SUB] airglow. [less ▲]

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See detailVenus express: Highlights of the nominal mission
Titov, D. V.; Svedhem, H.; Taylor, F. W. et al

in Solar System Research (2009), 43

Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit ... [more ▼]

Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit. The payload consists of seven experiments. It includes a powerful suite of remote sensing imagers and spectrometers, instruments for in-situ investigation of the circumplanetary plasma and magnetic field, and a radio science experiment. The spacecraft, based on the Mars Express bus modified for the conditions at Venus, provides a versatile platform for nadir and limb observations as well as solar, stellar, and radio occultations. In April 2006 Venus Express was inserted in an elliptical polar orbit around Venus, with a pericentre height of Ë 250 km and apocentre distance of Ë 66000 km and an orbital period of 24 hours. The nominal mission lasted from June 4, 2006 till October 2, 2007, which corresponds to about two Venus sidereal days. Here we present an overview of the main results of the nominal mission, based on a set of papers recently published in Nature, Icarus, Planetary and Space Science, and Geophysical Research Letters. [less ▲]

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See detailThe HARPS search for southern extra-solar planets. XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period
Forveille, T.; Bonfils, X.; Delfosse, X. et al

in Astronomy and Astrophysics (2009), 493

A 10.24-day Neptune-mass planet was recently announced as orbiting the nearby M2 dwarf Gl 176, based on 28 radial velocities measured with the HRS spectrograph on the Hobby-Heberly Telescope. We obtained ... [more ▼]

A 10.24-day Neptune-mass planet was recently announced as orbiting the nearby M2 dwarf Gl 176, based on 28 radial velocities measured with the HRS spectrograph on the Hobby-Heberly Telescope. We obtained 57 radial velocities of Gl 176 with the ESO 3.6 m telescope and the HARPS spectrograph, which is known for its sub-m s[SUP]-1[/SUP] stability. The median photon-noise standard error of our measurements is 1.1 m s[SUP]-1[/SUP], significantly lower than the 4.7 m s[SUP]-1[/SUP] of the HET velocities, and the 4-year period over which they were obtained overlaps considerably with the epochs of the HET measurements. The HARPS measurements show no evidence of a signal at the period of the putative HET planet, suggesting that its detection was spurious. We do find, on the other hand, strong evidence of a lower mass 8.4 M_Earth planet, in a quasi-circular orbit and at the different period of 8.78 days. The host star has moderate magnetic activity and rotates on a 39-day period, which we confirm through modulation of both contemporaneous photometry and chromospheric indices. We detect that period, as well, in the radial velocities, but it is well removed from the orbital period and offers no cause for confusion. This new detection of a super-Earth (2 M_Earth < M sin (i) < 10 M_Earth) around an M dwarf adds to the growing evidence that such planets are common around very low-mass stars. A third of the 20 known planets with M sin (i)< 0.1 M_Jup and 3 of the 7 known planets with M sin (i) < 10 M_Earth orbit an M dwarf, in contrast to just 4 of the ~300 known Jupiter-mass planets. Based on observations made with the HARPS instrument on the ESO 3.6-m telescope at La Silla Observatory under program ID 072.C-0488. [less ▲]

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See detailThe HARPS search for southern extra-solar planets. X. A m sin i = 11 M_â planet around the nearby spotted M dwarf <ASTROBJ>GJ 674</ASTROBJ>
Bonfils, X.; Mayor, M.; Delfosse, X. et al

in Astronomy and Astrophysics (2007), 474

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars that are significantly more massive or less ... [more ▼]

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars that are significantly more massive or less massive than the Sun, and in particular our radial velocity search for planets around very low-mass stars. Methods: As part of that program, we obtained measurements of <ASTROBJ>GJ 674</ASTROBJ>, an M 2.5 dwarf at d = 4.5 pc. These measurements have dispersion much in excess of their internal errors. An intensive observing campaign demonstrates that the excess dispersion is due to two superimposed coherent signals, with periods of 4.69 and 35 days. Results: These data are described well by a 2-planet Keplerian model where each planet has a ~11 M_â minimum mass. A careful analysis of the (low-level) magnetic activity of <ASTROBJ>GJ 674</ASTROBJ>, however, demonstrates that the 35-day period coincides with the stellar rotation period. This signal therefore originates in a spot inhomogeneity modulated by stellar rotation. The 4.69-day signal, on the other hand, is caused by a bona-fide planet, <ASTROBJ>GJ 674b</ASTROBJ>. Conclusions: Its detection adds to the growing number of Neptune-mass planets around M-dwarfs and reinforces the emerging conclusion that this mass domain is much more populated than the Jovian mass range. We discuss the metallicity distributions of M dwarf with and without planets and find a low 11% probability that they are drawn from the same parent distribution. Moreover, we find tentative evidence that the host star metallicity correlates with the total mass of their planetary system. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope under the GTO program ID 072.C-0488 at Cerro La Silla (Chile). Radial-velocity, photometric and Ca II H+K index time series are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strabg.fr/cgi-bin/qcat?J/A+A/474/293 [less ▲]

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See detailThe NO Martian Nightglow observed with the SPICAM UV Spectrometer and comparison with a one-dimensional model.
Cox, Cédric ULg; Saglam, A.; Gérard, Jean-Claude ULg et al

Conference (2007, April)

Observations in the 108-317 nm wavelength range have been performed with the SPICAM ultraviolet spectrometer aboard the Mars Express (MEX) mission. SPICAM has observed the ultraviolet nightglow emission ... [more ▼]

Observations in the 108-317 nm wavelength range have been performed with the SPICAM ultraviolet spectrometer aboard the Mars Express (MEX) mission. SPICAM has observed the ultraviolet nightglow emission in the δ (190-240 nm) and γ (225-270 nm) bands of nitric oxide (Bertaux et al. 2005). This emission arises from the recombination between O(3P) and N(4S) atoms that are produced on the day side to form NO in the night side. We present a summary of the night limb observations performed during the MEX mission. In particular, we describe the variability of the brightness and peak altitude. We find that the altitude of maximum emission varies between 55 and 90 km and the brightness is in the range 0.2 to 4.5 kR. We compare these observations with the results of a chemical-diffusive atmospheric model which solves the continuity equation for O, N(4S) and NO continuity equation using the finite volume method on one dimensional grid. The eddy coefficient, whose value is very uncertain, is a free parameter adjusted to match the observational data. [less ▲]

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See detailDYNAMO: a Mars upper atmosphere package for investigating solar wind interaction and escape processes, and mapping Martian fields
Chassefière, E.; Nagy, A.; Mandea, M. et al

in Advances in Space Research (2004), 33

DYNAMO is a small multi-instrument payload aimed at characterizing current atmospheric escape, which is still poorly constrained, and improving gravity and magnetic field representations, in order to ... [more ▼]

DYNAMO is a small multi-instrument payload aimed at characterizing current atmospheric escape, which is still poorly constrained, and improving gravity and magnetic field representations, in order to better understand the magnetic, geologic and thermal history of Mars. The internal structure and evolution of Mars is thought to have influenced climate evolution. The collapse of the primitive magnetosphere early in Mars history could have enhanced atmospheric escape and favored transition to the present arid climate. These objectives are achieved by using a low periapsis orbit. DYNAMO has been proposed in response to the AO released in February 2002 for instruments to be flown as a complementary payload onboard the CNES Orbiter to Mars (MO-07), foreseen to be launched in 2007 in the framework of the French PREMIER Mars exploration program. MO-07 orbital phase 2b (with an elliptical orbit of periapsis 170 km), and in a lesser extent 2a, offers an unprecedented opportunity to investigate by in situ probing the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, and therefore the present atmospheric escape rate. Ultraviolet remote sensing is an essential complement to characterize high, tenuous, layers of the atmosphere. One Martian year of operation, with about 5,000 low passes, should allow DYNAMO to map in great detail the residual magnetic field, together with the gravity field. Additional data on the internal structure will be obtained by mapping the electric conductivity, sinergistically with the NETLANDER magnetic data. Three options have been recommended by the International Science and Technical Review Board (ISTRB), who met on July 1st and 2nd, 2002. One of them is centered on DYNAMO. The final choice, which should be made before the end of 2002, will depend on available funding resources at CNES. [less ▲]

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