References of "Hubert, Benoît"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailInfluence of the crustal magnetic field on the Mars aurora electron flux and UV brightness
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Icarus (2017), 282

Observations with the SPICAM instrument on board Mars Express have shown the occasional presence of localized ultraviolet nightside emissions associated with enhanced energetic electron fluxes. These ... [more ▼]

Observations with the SPICAM instrument on board Mars Express have shown the occasional presence of localized ultraviolet nightside emissions associated with enhanced energetic electron fluxes. These features generally occur in regions with significant radial crustal magnetic field. We use a Monte-Carlo electron transport model to investigate the role of the magnetic field on the downward and upward electron fluxes, the brightness and the emitted power of auroral emissions. Simulations based on an ASPERA-3 measured auroral electron precipitation indicate that magnetic mirroring leads to an intensification of the energy flux carried by upward moving electrons- from about 20% in the absence of crustal magnetic field up to 33-78% when magnetic field is included depending on magnetic field topology. Conservation of the particle flux in a flux tube implies that the presence of the B-field does not appreciably modify the emission rate profiles for an initially isotropic pitch angle distribution. However, we find that crustal magnetic field results in increase of the upward electron flux, and, consequently, in reduction of the total auroral brightness for given energy flux of precipitating electrons. [less ▲]

Detailed reference viewed: 23 (3 ULg)
Full Text
See detailNitric Oxide nightglow as a tracer of inter-hemispheric circulation: Detailed comparison with the LMD-GCM
Stiepen, Arnaud ULg; IUVS team; Gonzales-Galindo et al

Conference (2016, September)

Detailed reference viewed: 13 (2 ULg)
Full Text
See detailAbel inversion method for cometary atmospheres.
Hubert, Benoît ULg; Opitom, Cyrielle ULg; Hutsemekers, Damien ULg et al

in Geophysical Research Abstracts (2016, April 01), 18

Remote observation of cometary atmospheres produces a measurement of the cometary emissions integrated along the line of sight joining the observing instrument and the gas of the coma. This integration is ... [more ▼]

Remote observation of cometary atmospheres produces a measurement of the cometary emissions integrated along the line of sight joining the observing instrument and the gas of the coma. This integration is the so-called Abel transform of the local emission rate. We develop a method specifically adapted to the inversion of the Abel transform of cometary emissions, that retrieves the radial profile of the emission rate of any unabsorbed emission, under the hypothesis of spherical symmetry of the coma. The method uses weighted least squares fitting and analytical results. A Tikhonov regularization technique is applied to reduce the possible effects of noise and ill-conditioning, and standard error propagation techniques are implemented. Several theoretical tests of the inversion techniques are carried out to show its validity and robustness, and show that the method is only weakly dependent on any constant offset added to the data, which reduces the dependence of the retrieved emission rate on the background subtraction. We apply the method to observations of three different comets observed using the TRAPPIST instrument: 103P/ Hartley 2, F6/ Lemmon and A1/ Siding spring. We show that the method retrieves realistic emission rates, and that characteristic lengths and production rates can be derived from the emission rate for both CN and C2 molecules. We show that the emission rate derived from the observed flux of CN emission at 387 nm and from the C2 emission at 514.1 nm of comet Siding Spring both present an easily-identifiable shoulder that corresponds to the separation between pre- and post-outburst gas. As a general result, we show that diagnosing properties and features of the coma using the emission rate is easier than directly using the observed flux. We also determine the parameters of a Haser model fitting the inverted data and fitting the line-of-sight integrated observation, for which we provide the exact analytical expression of the line-of-sight integration of the Haser model. [less ▲]

Detailed reference viewed: 13 (5 ULg)
Full Text
Peer Reviewed
See detailAn inversion method for cometary atmospheres
Hubert, Benoît ULg; Opitom, Cyrielle ULg; Hutsemekers, Damien ULg et al

in Icarus (2016), 277

Remote observation of cometary atmospheres produces a measurement of the cometary emissions integrated along the line of sight. This integration is the so-called Abel transform of the local emission rate ... [more ▼]

Remote observation of cometary atmospheres produces a measurement of the cometary emissions integrated along the line of sight. This integration is the so-called Abel transform of the local emission rate. The observation is generally interpreted under the hypothesis of spherical symmetry of the coma. Under that hypothesis, the Abel transform can be inverted. We derive a numerical inversion method adapted to cometary atmospheres using both analytical results and least squares fitting techniques. This method, derived under the usual hypothesis of spherical symmetry, allows us to retrieve the radial distribution of the emission rate of any unabsorbed emission, which is the fundamental, physically meaningful quantity governing the observation. A Tikhonov regularization technique is also applied to reduce the possibly deleterious effects of the noise present in the observation and to warrant that the problem remains well posed. Standard error propagation techniques are included in order to estimate the uncertainties affecting the retrieved emission rate. Several theoretical tests of the inversion techniques are carried out to show its validity and robustness. In particular, we show that the Abel inversion of real data is only weakly sensitive to an offset applied to the input flux, which implies that the method, applied to the study of a cometary atmosphere, is only weakly dependent on uncertainties on the sky background which has to be subtracted from the raw observations of the coma. We apply the method to observations of three different comets observed using the TRAPPIST telescope: 103P/ Hartley 2, F6/ Lemmon and A1/ Siding Spring. We show that the method retrieves realistic emission rates, and that characteristic lengths and production rates can be derived from the emission rate for both CN and C2 molecules. We show that the retrieved characteristic lengths can differ from those obtained from a direct least squares fitting over the observed flux of radiation, and that discrepancies can be reconciled for by correcting this flux by an offset (to which the inverse Abel transform is nearly not sensitive). The A1/Siding Spring observations were obtained very shortly after the comet produced an outburst, and we show that the emission rate derived from the observed flux of CN emission at 387 nm and from the C2 emission at 514.1 nm both present an easily-identifiable shoulder that corresponds to the separation between pre- and post-outburst gas. As a general result, we show that diagnosing properties and features of the coma using the emission rate is easier than directly using the observed flux, because the Abel transform produces a smoothing that blurs the signatures left by features present in the coma. We also determine the parameters of a Haser model fitting the inverted data and fitting the line-of-sight integrated observation, for which we provide the exact analytical expression of the line-of-sight integration of the Haser model. [less ▲]

Detailed reference viewed: 38 (6 ULg)
Full Text
Peer Reviewed
See detailWhat controls the local time extent of flux transfer events?
Milan, S. E.; Imber, S. M.; Carter, J. A. et al

in Journal of Geophysical Research. Space Physics (2016), 121

Detailed reference viewed: 24 (3 ULg)
Full Text
Peer Reviewed
See detailScientific Problems Addressed by the Spektr-UV Space Project (World Space Observatory—Ultraviolet)
Boyarchuk, A.A.; others; Gérard, Jean-Claude ULg et al

in Astronomy Reports (2016), 60(1), 1-42

The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These ... [more ▼]

The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory—Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115–310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems. [less ▲]

Detailed reference viewed: 25 (1 ULg)
Full Text
Peer Reviewed
See detailNonthermal radiative transfer of oxygen 98.9 nm ultraviolet emission: Solving an old mystery
Hubert, Benoît ULg; Gérard, Jean-Claude; Shematovich, Valery I. et al

in Journal of Geophysical Research. Space Physics (2015), 120

Sounding rocket measurements conducted in 1988 under high solar activity conditions revealed that the intensity of thermospheric OI emissions at 98.9 nm present an anomalous vertical profile, showing ... [more ▼]

Sounding rocket measurements conducted in 1988 under high solar activity conditions revealed that the intensity of thermospheric OI emissions at 98.9 nm present an anomalous vertical profile, showing exospheric intensities much higher than expected from radiative transfer model results, which included the known sources of excited oxygen. All attempts based on modeling of the photochemical processes and radiative transfer were unable to account for the higher than predicted brightnesses. More recently, the SOHO-SUMER instrument measured the UV solar flux at high spectral resolution, revealing the importance of a significant additional source of oxygen emission at 98.9 nm that had not been accounted for before. In this study, we simulate the radiative transfer of the OI-98.9 nm multiplet, including the photochemical sources of excited oxygen, the resonant scattering of solar photons, and the effects of non-thermal atoms, i.e. a population of fast-moving oxygen atoms in excess of the Maxwellian distribution. Including resonance scattering of the 98.9 nm solar multiplet, we find good agreement with the previous sounding rocket observation. The inclusion of a nonthermal oxygen population with a consistent increase of the total density produces a larger intensity at high altitude that apparently better accounts for the observation, but such a correction cannot be demonstrated given the uncertainties of the observations. A good agreement between model and sounding rocket observation is also found with the triplet at 130.4 nm. We further investigate the radiative transfer of the OI-98.9 nm multiplet, and the oxygen emissions at 130.4 and 135.6 nm using observations from the STP78-1 satellite. We find a less satisfying agreement between the model and the STP78-1 data that can be accounted for by scaling the modelled intensity within a range acceptable given the uncertainties on the STP78-1 absolute calibration. [less ▲]

Detailed reference viewed: 18 (6 ULg)
Full Text
Peer Reviewed
See detailMonte Carlo Simulation of Metastable Oxygen Photochemistry in Cometary Atmospheres
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Astrophysical Journal (2015), 798

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical ... [more ▼]

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical processes lead to the production of other species generally absent from the nucleus, such as OH. Although all comets are different, they all have a highly rarefied atmosphere, which is an ideal environment for nonthermal photochemical processes to take place and influence the detailed state of the atmosphere. We develop a Monte Carlo model of the coma photochemistry. We compute the energy distribution functions (EDF) of the metastable O([SUP]1[/SUP]D) and O([SUP]1[/SUP]S) species and obtain the red (630 nm) and green (557.7 nm) spectral line shapes of the full coma, consistent with the computed EDFs and the expansion velocity. We show that both species have a severely non-Maxwellian EDF, that results in broad spectral lines and the suprathermal broadening dominates due to the expansion motion. We apply our model to the atmosphere of comet C/1996 B2 (Hyakutake) and 103P/Hartley 2. The computed width of the green line, expressed in terms of speed, is lower than that of the red line. This result is comparable to previous theoretical analyses, but in disagreement with observations. We explain that the spectral line shape does not only depend on the exothermicity of the photochemical production mechanisms, but also on thermalization, due to elastic collisions, reducing the width of the emission line coming from the O([SUP]1[/SUP]D) level, which has a longer lifetime. [less ▲]

Detailed reference viewed: 25 (5 ULg)
Full Text
Peer Reviewed
See detailForbidden oxygen lines at various nucleocentric distances in comets
Decock, Alice ULg; Jehin, Emmanuel ULg; Rousselot, P. et al

in Astronomy and Astrophysics (2015), 573

Aims: We study the formation of the [OI] lines - that is, 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the two red lines) - in the coma of comets and determine the parent species of the oxygen ... [more ▼]

Aims: We study the formation of the [OI] lines - that is, 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the two red lines) - in the coma of comets and determine the parent species of the oxygen atoms using the ratio of the green-to-red-doublet emission intensity, I[SUB]5577[/SUB]/(I[SUB]6300[/SUB] + I[SUB]6364[/SUB]), (hereafter the G/R ratio) and the line velocity widths. <BR /> Methods: We acquired high-resolution spectroscopic observations at the ESO Very Large Telescope of comets C/2002 T7 (LINEAR), 73P-C/Schwassmann-Wachmann 3, 8P/Tuttle, and 103P/Hartley 2 when they were close to Earth (<0.6 au). Using the observed spectra, which have a high spatial resolution (<60 km/pixel), we determined the intensities and widths of the three [OI] lines. We spatially extracted the spectra to achieve the best possible resolution of about 1-2'', that is, nucleocentric projected distances of 100 to 400 km depending on the geocentric distance of the comet. We decontaminated the [OI] green line from C[SUB]2[/SUB] lines blends that we identified. <BR /> Results: The observed G/R ratio in all four comets varies as a function of nucleocentric projected distance (between ~0.25 to ~0.05 within 1000 km). This is mainly due to the collisional quenching of O([SUP]1[/SUP]S) and O([SUP]1[/SUP]D) by water molecules in the inner coma. The observed green emission line width is about 2.5 km s[SUP]-1[/SUP] and decreases as the distance from the nucleus increases, which can be explained by the varying contribution of CO[SUB]2[/SUB] to the O([SUP]1[/SUP]S) production in the innermost coma. The photodissociation of CO[SUB]2[/SUB] molecules seem to produce O([SUP]1[/SUP]S) closer to the nucleus, while the water molecule forms all the O([SUP]1[/SUP]S) and O([SUP]1[/SUP]D) atoms beyond 10[SUP]3[/SUP] km. Thus we conclude that the main parent species producing O([SUP]1[/SUP]S) and O([SUP]1[/SUP]D) in the inner coma is not always the same. The observations have been interpreted in the framework of the previously described coupled-chemistry-emission model, and the upper limits of the relative abundances of CO[SUB]2[/SUB] were derived from the observed G/R ratios. Measuring the [OI] lines might provide a new way to determine the CO[SUB]2[/SUB] relative abundance in comets. Based on observations made with ESO Telescope at the La Silla Paranal Observatory under programs ID 073.C-0525, 277.C-5016, 080.C-0615 and 086.C-0958.Tables 3 and 4 are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424403/olm">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 24 (4 ULg)
Full Text
Peer Reviewed
See detailThe EChO science case
Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul et al

in Experimental Astronomy (2015), 1502

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general ... [more ▼]

The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional diversity observed as compared to the Solar System? EChO (Exoplanet Characterisation Observatory) has been designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large and diverse planet sample within its four-year mission lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300K-3000K) of F to M-type host stars. Over the next ten years, several new ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets. Placing the satellite at L2 provides a cold and stable thermal environment, as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. A 1m class telescope is sufficiently large to achieve the necessary spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16 micron) and SNR to be achieved by EChO, thanks to its high stability and dedicated design, would enable a very accurate measurement of the atmospheric composition and structure of hundreds of exoplanets. [less ▲]

Detailed reference viewed: 78 (45 ULg)
Full Text
Peer Reviewed
See detailMagnetic Reconnection During Major Magnetospheric Storms
Hubert, Benoît ULg; Milan, S.E.; Cowley, S.W.H.

Poster (2014, December)

We combine imaging of the proton aurora from the SI12-IMAGE instrument with ionospheric convection measurement from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of ... [more ▼]

We combine imaging of the proton aurora from the SI12-IMAGE instrument with ionospheric convection measurement from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of the Earth magnetosphere. Interaction between the solar wind and the Earth geomagnetic environment causes a reconfiguration of the magnetic field that connects the interplanetary magnetic field (IMF) to the geomagnetic field. This reconnection process produces open magnetic field lines (i.e. field lines of the magnetosphere that close through the interplanetary medium) that are dragged to the magnetotail by the solar wind flow, where they eventually reconnect again, back to a closed topology. The SI12 imaging of the Doppler-shifted Lyman-α emission of the proton aurora is used to estimate the location of the boundary separating open and closed field lines at ionospheric altitude. We then estimate the open magnetic flux of the Earth magnetosphere, encircled by this boundary. The rate of reconnection causing a variation of the open magnetic flux can be expressed as a voltage in application of Faraday’s law. This voltage is measured along the open/closed field line boundary determined from the imaging data. The electric field associated with the voltage has two origins: motion of the boundary and the ionospheric field. We use the ionospheric electric field deduced from ionospheric convection measurement from the SuperDARN to estimate the reconnection voltage at the magnetopause (flux opening) and in the magnetotail (flux closure) accounting for the motion of the open/closed field line boundary determined from the SI12 images. The method is applied during several (strong) geomagnetic storms. These intervals are characterized by large values of open flux and reconnection rates, as a result of coupling between the solar wind and the geomagnetic environment. We present these results in terms of a magnetospheric mode that develops under strong coupling with the solar wind, a condition known to be prone to the development of sawtooth events, characterized by overloading of the magnetosphere with open magnetic flux. [less ▲]

Detailed reference viewed: 56 (1 ULg)
Peer Reviewed
See detailMagnetospheric modes and magnetic reconnection.
Hubert, Benoît ULg; Milan, S.E.; Cowley, S.W.H.

Poster (2014, November)

We combine imaging of the proton aurora from the SI12-IMAGE instrument with measurement of the ionospheric convection from the SuperDARN radar network to analyze the cycle of magnetic flux opening and ... [more ▼]

We combine imaging of the proton aurora from the SI12-IMAGE instrument with measurement of the ionospheric convection from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of the Earth magnetosphere. Interaction between the solar wind and the Earth geomagnetic environment causes a reconfiguration of the magnetic field that connects the interplanetary magnetic field (IMF) to the geomagnetic field. This reconnection process produces open magnetic field lines (i.e. field lines of the magnetosphere that close through the interplanetary medium) that are dragged to the magnetotail by the solar wind flow, where they eventually reconnect again, back to a closed topology. The SI12 imaging of the Doppler-shifted Lyman-α emission of the proton aurora is used to estimate the location of the boundary separating open and closed field lines at ionospheric altitude. We then estimate the open magnetic flux of the Earth magnetosphere, encircled by this boundary. The rate of reconnection causing a variation of the open magnetic flux can be expressed as a voltage in application of Faraday’s law. This voltage is measured along the open/closed field line boundary determined from the imaging data. The electric field associated with the voltage has two origins: motion of the boundary and the ionospheric field. We use the ionospheric electric field deduced from ionospheric convection measurement from the SuperDARN to estimate the reconnection voltage at the magnetopause (flux opening) and in the magnetotail (flux closure) accounting for the motion of the open/closed field line boundary determined from the SI12 images. The method is applied during substorms, steady geomagnetic convection intervals, sawtooth events and geomagnetic storms. These different intervals are characterized by different values of open flux and reconnection rates, as a result of different coupling between the solar wind and the geomagnetic environment. We interpret these differences as different dynamic modes of the magnetospheric system. Shock-induced flux closure events are also presented, as an exceptional situation that differs from the modes presented above. [less ▲]

Detailed reference viewed: 74 (2 ULg)
Full Text
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)

Detailed reference viewed: 15 (2 ULg)
Full Text
Peer Reviewed
See detailDetermination of ITM Key Parameters By the Ionospheric Connection Explorer (ICON)
Immel, T. J.; England, S.; Mende, S. B. et al

Conference (2014)

Detailed reference viewed: 14 (2 ULg)
Full Text
Peer Reviewed
See detailIonization Fraction in the Thermosphere of the Exoplanet HD 209458b
Ionov, D. E.; Bisikalo, D. V.; Shematovich, V. I. et al

in Solar System Research (2014), 48

Detailed reference viewed: 8 (1 ULg)
Peer Reviewed
See detailNonthermal O(1S) and O(1D) populations in cometary atmospheres
Hubert, Benoît ULg; Bisikalo, D.V.; Shematovich, V.I. et al

Conference (2013, December)

Recent developments in the field of cometary science have motivated many studies dealing with the nucleus composition and mineralogy, and also with the photochemistry of the coma. In particular, ground ... [more ▼]

Recent developments in the field of cometary science have motivated many studies dealing with the nucleus composition and mineralogy, and also with the photochemistry of the coma. In particular, ground based observations have shown that the visible oxygen emissions at 557.7 and 630 nm, both belonging to the Rosetta-VIRTIS-M passband, present different line profiles, pointing to specific photochemical processes. In this work, we present a Monte Carlo simulation of the O(1D) and O(1S) photochemistry including photodissociation of H2O, CO2 and CO, quenching, collisional thermalization and radiative decay. The model solves Boltzmann's integro differential equation including sources and sinks, as well as a prescribed expansion velocity of the coma. The energy distribution functions (EDF's) of O(1S) and O(1D) are computed at cometocentric distances ranging between 10 and 5000 km. We find that the EDF's of both O(1D) and O(1S) are strongly nonthermal, up to a degree that sharply varies with cometocentric distance, as thermalization is less efficient when the density of the dominant species is reduced. It follows that the Doppler profile of the visible radiations emitted by both species is non-gaussian in a frame of reference moving with the expanding coma. The nonthermal volume emission rate is then integrated along a set of chosen line of sights, accounting for the explicit Doppler profiles derived from the EDF's as well as the expansion motion, and the Doppler profile of the full coma is computed. It appears that most of the line width is due to the expansion motion, although the detailed line shape remains sensitive to the nonthermal nature of the EDF's. Our computation can then be compared with the line profiles observed from the ground with the UVES spectrograph mounted on the ESO-VLT. [less ▲]

Detailed reference viewed: 43 (0 ULg)
See detailICON: The Ionospheric Connection Explorer - NASA's Next Space Physics and Aeronomy Mission
Immel, T. J.; Mende, S. B.; Heelis, R. A. et al

Conference (2013)

Detailed reference viewed: 10 (1 ULg)
See detailAnomalous OI-989 Å intensity profile: solving an old mystery.
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Shematovich, Valery I. et al

Poster (2012, December 06)

Sounding rocket measurements conducted in 1988 under high solar activity conditions had revealed that the intensity of the thermospheric OI emission at 989 Å presents an anomalous vertical profile ... [more ▼]

Sounding rocket measurements conducted in 1988 under high solar activity conditions had revealed that the intensity of the thermospheric OI emission at 989 Å presents an anomalous vertical profile. Observation presents an intensity much higher than what can be expected compared with theoretical results including the photochemical sources of excited oxygen and the radiative transfer of the photons of the OI-989 sextuplet especially above the exobase. Attempts were conducted to clarify the discrepancy by including the non-thermal O(3P) population that appears around the exobase and higher, and that can scatter Doppler-shifted photons of the line profile farther from the rest wavelength. All attempts based on detail modeling of the photochemical processes and radiative transfer revealed unable to account for the discrepancy. Recently the FUV and EUV solar flux has been obtained at very high spectral resolution with the SOHO-SUMER instrument, revealing a significant solar oxygen emission at 989 Å, i.e. a source of photons that had never been accounted for before. In this study, we compute the radiative transfer of the OI-989 Å multiplet including the photochemical sources of excited oxygen, the scattering of incident solar photons and the effect of non-thermal atoms. We find a good agreement with the previous sounding rocket observation, solving the old mystery. We also compare the model simulations with the observations of the STP-78 satellite to better determine the relative importance of the various parameters at work in the radiative transfer of the OI-989 Å multiplet. [less ▲]

Detailed reference viewed: 8 (1 ULg)
Full Text
See detailKuaFu: exploring the Sun-Earth connection
Milan, Steve; Dunlop, Malcolm; Fazakerley, Andrew et al

in Astronomy and Geophysics (2012), 53

Steve Milan and the KuaFu team explain why this space mission will provide space weather data that will help to understand and mitigate the risks it poses to our increasingly technological society.

Detailed reference viewed: 25 (2 ULg)