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See detailHST observations of Europa's atmospheric UV emission
Saur, J.; Feldman, P. D.; Strobel, D. F. et al

Conference (2009, July 27)

Detailed reference viewed: 7 (2 ULg)
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See detailHST Observations of Gravitationally Lensed QSOs
Claeskens, Jean*-François; Sluse, Dominique; Surdej, Jean ULg

in Macchetto, D. F. (Ed.) The Impact of HST on European Astronomy (2010)

Thanks to its sharp view, HST has significantly improved our knowledge of tens of gravitationally lensed quasars in four different respects: (1) confirming their lensed nature; (2) detecting the lensing ... [more ▼]

Thanks to its sharp view, HST has significantly improved our knowledge of tens of gravitationally lensed quasars in four different respects: (1) confirming their lensed nature; (2) detecting the lensing galaxy responsible for the image splitting; (3) improving the astrometric accuracy on the positions of the unresolved QSO images and of the lens; (4) resolving extended lensed structures from the QSO hosts into faint NIR or optical rings or arcs. These observations have helped to break some degeneracies on the lens potential, to probe the galaxy evolution and to reconstruct the true shape of the QSO host with an increased angular resolution. [less ▲]

Detailed reference viewed: 13 (1 ULg)
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See detailHST observations of gravitationally lensed QSOs
Claeskens, Jean-François ULg; Sluse, Dominique; Surdej, Jean ULg

in proceedings of the 41st ESLAB Symposium "The Impact of HST on European Astronomy" (June 2007) (2008, June)

Thanks to its sharp view, HST has significantly improved our knowledge of tens of gravitationally lensed quasars in four different respects: (1) confirming their lensed nature; (2) detecting the lensing ... [more ▼]

Thanks to its sharp view, HST has significantly improved our knowledge of tens of gravitationally lensed quasars in four different respects: (1) confirming their lensed nature; (2) detecting the lensing galaxy responsible for the image splitting; (3) improving the astrometric accuracy on the positions of the unresolved QSO images and of the lens; (4) resolving extended lensed structures from the QSO hosts into faint NIR or optical rings or arcs. These observations have helped to break some degeneracies on the lens potential, to probe the galaxy evolution and to reconstruct the true shape of the QSO host with an increased angular resolution. [less ▲]

Detailed reference viewed: 36 (17 ULg)
See detailHST Observations of Jupiter's Aurora Simultaneous with GALILEO Measurements
Clarke, J. T.; Ballester, G.; Trauger, J. et al

in Bulletin of the American Astronomical Society (1997, July 01)

An HST observing program is underway to obtain images and spectra of Jupiter's ultraviolet aurora during key events in the GALILEO orbiter mission, including remote observations of the nightside aurora ... [more ▼]

An HST observing program is underway to obtain images and spectra of Jupiter's ultraviolet aurora during key events in the GALILEO orbiter mission, including remote observations of the nightside aurora and measurements of the magnetic field and charged particle environments. We have obtained WFPC 2 images and GHRS spectra of Jupiter's aurora overlapping with GALILEO measurements during GALILEO orbits G1 (June 1996), G2 (Sept. 1996), G7 (April 1997), and G8 (May 1997), and at the time of writing we are scheduling STIS spectra for summer 1997. The WFPC 2 images appear similar to earlier reported auroral images, with the main oval at the same location observed over the last 2 years, rapidly variable emission poleward of the main oval, and the Io footprint with a similar longitudinal offset from the local magnetic field. Spectra were obtained of auroral emission features including the northern and southern main ovals, the diffuse emission poleward of the main oval, and the northern and southern Io footprints. These spectra will be presented with estimates of the overlying hydrocarbon columns, the energy of the exciting electrons, the rotational temperature of the emitting hydrogen, and the overlying column of atomic hydrogen. This work was supported by NASA under contract JPL 959122 and grants GO-5828.01-94A and GO-6743.01-95A to the University of Michigan. [less ▲]

Detailed reference viewed: 5 (1 ULg)
See detailHST observations of Jupiter's aurorae - What can we learn from the Io UV footprint?
Bonfond, Bertrand ULg

Scientific conference (2008, December 11)

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See detailHST observations of the gravitational lens systems HE 1104-1805 and J03.13
Remy, M.; Claeskens, Jean-François ULg; Surdej, Jean ULg

in Casertano, S. (Ed.) The 1997 HST Calibration Workshop with a New Generation of Instruments (1997, January 01)

High angular resolution Principle Component Image (PC1) images of the gravitational lens systems HE 1104-1805 and J03.13 are presented. Using a method described in Remy et al. (1997a), optimal TinyTim ... [more ▼]

High angular resolution Principle Component Image (PC1) images of the gravitational lens systems HE 1104-1805 and J03.13 are presented. Using a method described in Remy et al. (1997a), optimal TinyTim Point Spread Function (PSFs) are constructed to fit at best the lensed point-like components. The derived photometry of the GL components and the detection of the lens galaxy for HE 1104-1805 are discussed. Textbook case Faint Object Spectrograph (FOS) spectra of J03.13 A and B clearly show that this double QSO is a cosmic mirage. [less ▲]

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Peer Reviewed
See detailHST observations of the QSO pair Q1026-0045A,B
Petitjean, Patrick; Surdej, Jean ULg; Smette, Alain et al

in Astronomy and Astrophysics (1998), 334

The spatial distribution of the Lyalpha forest is studied using new HST data for the quasar pair Q 1026-0045 A and B at z_em = 1.438 and 1.520 respectively. The angular separation is 36 arcsec and ... [more ▼]

The spatial distribution of the Lyalpha forest is studied using new HST data for the quasar pair Q 1026-0045 A and B at z_em = 1.438 and 1.520 respectively. The angular separation is 36 arcsec and corresponds to transverse linear separations between lines of sight of ~ 300h(-1}_{50) kpc (q_o = 0.5) over the redshift range 0.833 < z < 1.438. From the observed numbers of coincident and anti-coincident Lyalpha absorption lines, we conclude that, at this redshift, the Lyalpha structures have typical dimensions of ~ 500h(-1}_{50) kpc, larger than the mean separation of the two lines of sight. The velocity difference, Delta V, between coincident lines is surprisingly small (4 and 8 pairs with Delta V < 50 and 200 km s(-1) respectively). Metal line systems are present at z_abs = 1.2651 and 1.2969 in A, z_abs = 0.6320, 0.7090, 1.2651 and 1.4844 in B. In addition we tentatively identify a weak Mg ii system at z_abs = 0.11 in B. It is remarkable that the z_abs = 1.2651 system is common to both lines of sight. The system at z_abs = 1.4844 has strong O vi absorption. There is a metal-poor associated system at z_abs = 1.4420 along the line of sight to A with complex velocity profile. We detect a strong Lyalpha absorption along the line of sight to B redshifted by only 300 km s(-1) relatively to the associated system. It is tempting to interpret this as the presence of a disk of radius larger than 300h(-1}_{50) kpc surrounding quasar A. Based on observations obtained with the NASA/ESA Hubble Space Telescope by the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555 [less ▲]

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Peer Reviewed
See detailHST spectra of the Jovian ultraviolet aurora: Search for heavy ion precipitation
Trafton, L. M.; Dols, V.; Gérard, Jean-Claude ULg et al

in Astrophysical Journal (1998), 507(2), 955-967

Ultraviolet spectra using Hubble Space Telescope sampled between 1250 and 1680 Angstrom, at spectral resolution less than or equal to 0.57 Angstrom are reported for characteristically bright regions of ... [more ▼]

Ultraviolet spectra using Hubble Space Telescope sampled between 1250 and 1680 Angstrom, at spectral resolution less than or equal to 0.57 Angstrom are reported for characteristically bright regions of Jupiter's morning and afternoon northern aurora. Several observed spectra exhibit sharply enhanced resolution. We interpret this as bright auroral emission foreshortened on the morning limb with a maximum intensity at least as high as 2000 kR. We have searched for evidence that the primary precipitating particles exciting the aurora include the heavy ions known to exist in Jupiter's plasma torus and magnetosphere. We have also searched for such ambient heavy ions and neutrals at rest in the auroral ionosphere, the end products of previous precipitation, excited by the auroral cascade. We argue that primary emission would be characterized by a dramatically Doppler-broadened (similar to 10-15 Angstrom) and redshifted line profile resulting from the cascade process and the angle between the line of sight and the magnetic field lines in the atmosphere. In contrast, ambient emission would be distinguished by narrow emission lines. We have modeled the theoretical sulfur and oxygen line shapes for ion precipitation and conclude that electron precipitation is responsible for most of the H-2 emissions. O ions contributed <13% of the precipitating energy flux, and S ions contributed < 50%. This dominance suggests that field-aligned magnetospheric currents are more important than energetization of energetic ions and subsequent scattering by plasma waves as a mechanism for generating the Jovian aurora. We set an upper limit over our spectra of 35-43 R to the emission from ambient oxygen and sulfur ions and their neutrals, except that for the S II 1256 triplet, the upper limit for the nominally brightest line, at 1260 Angstrom, is 74 R. Hence, we find no evidence for the accumulation of sulfur in the auroral ionosphere. A single narrow emission line from an unidentified ambient specie near 1254 Angstrom may be detected at the 4 sigma level, introducing the possibility of complex auroral aeronomy. Differences were observed in the auroral spectral hydrocarbon absorption at different locations, which cannot be interpreted without ambiguity between auroral and atmospheric structural causes. We have found that the brighter emission in an auroral sector consistently shows more spectral hydrocarbon absorption than the dimmer emission. We suggest two alternative physical explanations for this phenomenon. [less ▲]

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Peer Reviewed
See detailHST STIS observations of four QSO pairs
Aracil, B.; Petitjean, P.; Smette, A. et al

in Astronomy and Astrophysics (2002), 391(1), 1-12

We present HST STIS observations of four quasar pairs with redshifts 0.84<z(em)<1.56 and angular separation 2-3 arcmin corresponding to ∼1-1.5 h(50)(-1) Mpc transverse proper distance at zsimilar to0.9 ... [more ▼]

We present HST STIS observations of four quasar pairs with redshifts 0.84<z(em)<1.56 and angular separation 2-3 arcmin corresponding to ∼1-1.5 h(50)(-1) Mpc transverse proper distance at zsimilar to0.9. We study the distribution of velocity differences between nearest neighbor HI Lyman-alpha absorption lines detected in the spectra of adjacent QSOs in order to search for the possible correlation caused by the extent or the clustering properties of the structures traced by the absorption lines over such a scale. The significance of the correlation signal is determined by comparison with Monte-Carlo simulations of spectra with randomly distributed absorption lines. We find an excess of lines with a velocity separation smaller than DeltaV=500 km s(-1) significant at the 99.97% level. This clearly shows that the Lyman-alpha forest is correlated on scales larger than 1 h(50)(-1) Mpc at zsimilar to1. However, out of the 20 detected coincidences within this velocity bin, 12 have V>200 km s(-1). This probably reflects the fact that the scale probed by our observations is not related to the real size of individual absorbers but rather to large scale correlation. Statistics are too small to conclude about any difference between pairs separated by either 2 or 3 arcmin. A damped Lyman-alpha system is detected at z(abs)=1.2412 toward LBQS 0019-0145A with log N(HI)similar to20.5. From the absence of ZnII absorption, we derive a metallicity relative to solar [Zn/H]< -1.75. [less ▲]

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See detailHST STIS Observations of Saturn's Auroral Variations Concurrent with the Cassini Solar Wind Campaign in Jan. 2004
Clarke, J. T.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2004, May 17)

Saturn's magnetosphere is often referred to as "intermediate between the cases of the Earth and Jupiter". Due to very limited measurements of Saturn's magnetosphere and auroral activity, however, it has ... [more ▼]

Saturn's magnetosphere is often referred to as "intermediate between the cases of the Earth and Jupiter". Due to very limited measurements of Saturn's magnetosphere and auroral activity, however, it has never been clear in detail what this statement means. A recent campaign of HST STIS UV imaging of Saturn's aurora has been carried out over 8-30 Jan. 2004 concurrent with measurements of the approaching solar wind by Cassini. This imaging set is much more comprehensive than any earlier observations of Saturn's aurora, obtained at a time when Saturn's southern auroral oval is completely visible due to the large apparent tilt of Saturn. The data provide the opportunity to determine the mean distribution of the auroral emissions, the degree of corotation of any bright regions, any variations with local time of the emissions, the latitudinal motions of the main oval with time and location, and other parameters. In addition, each of these can be compared with the approaching solar wind conditions and Saturn's kilometric radiation (SKR) intensity from Cassini measurements. Quick looks at the data from HST and Cassini demonstrate that the measurements have been made successfully, and the coverage includes dramatic variations in Saturn's auroral activity as well as at least two solar wind shocks passing Cassini. This presentation will concentrate on the measured properties of Saturn's aurora in the context of comparisons with the magnetospheres of the Earth and Jupiter. [less ▲]

Detailed reference viewed: 22 (5 ULg)
See detailThe HST UV Auroral Imaging Campaign of Jupiter and Saturn during the International Heliophysical Year
Clarke, J. T.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2006, December 01)

An extended campaign of observations of the UV auroral emissions from Jupiter and Saturn is scheduled for three periods beginning in Jan. 2007 and ending in late June 2008. This will be by far the most ... [more ▼]

An extended campaign of observations of the UV auroral emissions from Jupiter and Saturn is scheduled for three periods beginning in Jan. 2007 and ending in late June 2008. This will be by far the most extensive series of remote high resolution imaging of planetary aurora to date, and should provide new physical insight into the cause and effect relationships governing the controlling processes for the giant planet auroral emissions. These observations will overlap with in situ measurements of local solar wind and magnetospheric plasma conditions by Cassini at Saturn in Jan. 2007 and by the New Horizons mission approaching Jupiter in Feb. 2007. The UV auroral emission brightness and distributions will also be compared with extrapolated estimates of the solar wind conditions near each planet from periods just before planetary opposition in Jan. 2007 (Saturn) and June 2007 (Jupiter). The HST observations will also be coordinated with ground-based observations of near-IR auroral and nonthermal radio emissions. This paper will give an overview of the program, including the schedule of HST observations and the schedule of known coordinated observations. While a preliminary schedule has been submitted for the HST observations, this schedule will be finalized only when the HST orbit is sufficiently well known for the periods of observation for detailed pointing to be specified. By the time of Fall AGU, it should be possible to show the detailed schedule and pointing for the Jan-Feb 2007 observations. The paper will include a presentation of the plans for the rapid reduction and distribution of the HST auroral images to the community. [less ▲]

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See detailHST UV Imaging of Saturn's Southern Aurora during Simultaneous Cassini Imaging of the Northern Aurora
Clarke, J. T.; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

Conference (2005, May 01)

On 17 Feb. 2005, one week after the AGU abstract deadline, Hubble Space Telescope (HST) observations are scheduled with the Advanced Camera for Surverys (ACS) to image Saturn's UV aurora for a period of 5 ... [more ▼]

On 17 Feb. 2005, one week after the AGU abstract deadline, Hubble Space Telescope (HST) observations are scheduled with the Advanced Camera for Surverys (ACS) to image Saturn's UV aurora for a period of 5 HST orbits, or 8 hours, corresponding to 0.7 of one Saturn rotation. In the present epoch, observations from the Earth can observe nearly the entire southern auroral oval in sunlight, but none of the northern oval, due to the tilt of Saturn's axis. Over the same period, a Cassini imaging sequence will scan across the northern nightside auroral emission region from the nightside of the planet. This presents a unique opportunity to determine the relationship between the conjugate points in the auroral emission regions, along with charged particle and magnetic field measurements in the nightside Saturn magnetosphere. This campaign of observations will be presented in this paper, with a concentration on the HST images, along with scientific conclusions as appropriate. [less ▲]

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See detailHST-FOC observations of a remarkable UV auroral event on Jupiter
Gérard, Jean-Claude ULg; Grodent, Denis ULg; Prangé, R. et al

in NASA STI/Recon Technical Report N (1994), 95

Two sets of UV (ultraviolet) images of the Jovian north aurora were obtained with the Faint Object Camera (FOC) on Hubble. The first series shows a very intense discrete arc in corotation with the planet ... [more ▼]

Two sets of UV (ultraviolet) images of the Jovian north aurora were obtained with the Faint Object Camera (FOC) on Hubble. The first series shows a very intense discrete arc in corotation with the planet. The maximum apparent H2 emission rate corresponds to an electron precipitation of approximately 1/sq Wm, a very large flux in comparison with the solar EUV (extreme ultraviolet) heating. The hugh particle heating rate of the auroral upper atmosphere of Jupiter is expected to cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours later, the discrete arc had considerably decreased in brightness. The timescale and magnitude of the change in the UV aurora strongly suggests that the discrete Jovian auroral precipitation is related to large scale current system variations as are the Earth's discrete aurorae. [less ▲]

Detailed reference viewed: 4 (1 ULg)
See detailHST-STIS Observations of Jupiter's Aurora
Clarke, J. T.; Ajello, J.; Ballester, G. E. et al

in Bulletin of the American Astronomical Society (1998, September 01)

HST observations of the UV emissions from Jupiter's aurora have been obtained with the new Space Telescope Imaging Spectrograph (STIS) since July 1997. UV images of the aurora are now possible with an ... [more ▼]

HST observations of the UV emissions from Jupiter's aurora have been obtained with the new Space Telescope Imaging Spectrograph (STIS) since July 1997. UV images of the aurora are now possible with an order of magnitude higher sensitivity than possible with earlier cameras, and improved angular resolution from shorter exposures. Images have been obtained at 4 epochs since Sept. 1997, and reveal several new features of the auroral emission pattern. These include i) faint auroral emissions extending roughly 60 deg. in the wake or plasma flow direction beyond Io's magnetic footprint, ii) systematic motions of the main auroral oval both toward the pole and toward the equator at different local times and longitudes, and iii) clear identification of an auroral emission feature with Ganymede's magnetic footprint, from the relative motion of the feature remaining underneath Ganymede in a time series of images. Preliminary interpretations of these features will be presented. Spectra have also been obtained of auroral emission features including the northern and southern main ovals, the diffuse emission poleward of the main oval, and the northern and southern Io footprints. These spectra will be presented with estimates of the overlying hydrocarbon columns, the energy of the exciting electrons, the rotational temperature of the emitting hydrogen, and the overlying column of atomic hydrogen. This work was supported by NASA under grants GO-6743.01-95A and GO-7308.01-96A to the University of Michigan. [less ▲]

Detailed reference viewed: 6 (1 ULg)
See detailHST-STIS Observations of Jupiter's FUV Aurora During the Cassini-Jupiter Flyby
Grodent, Denis ULg; Clarke, J. T.; Kim, J.

Poster (2001, June 25)

Detailed reference viewed: 1 (0 ULg)
See detailHST/ACS UV Imaging of Saturn's Southern Aurora in a Quiet State
Wannawichian, S.; Clarke, J. T.; Gérard, Jean-Claude ULg et al

Conference (2005, December 01)

Prior observations of Saturn's aurora have suggested that the aurora are highly variable, with much of the activity controlled by conditions in the solar wind. Observations of Saturn's UV aurora on 17 ... [more ▼]

Prior observations of Saturn's aurora have suggested that the aurora are highly variable, with much of the activity controlled by conditions in the solar wind. Observations of Saturn's UV aurora on 17 February 2005 were performed with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) to further test this. The UV Solar Blind Camera (SBC) imaged the UV emissions from 115.0 to 170.0 nm for a period of 5 HST orbits, or 8 hours, corresponding to 74% of a Saturn rotation. In that observation period, HST imaged the southern auroral region in sunlight, but not the northern auroral region because of the tilt of Saturn rotation axis. Saturn's aurora appeared in its most quiet state, comparable or fainter than those observed by HST's Space Telescope Imaging Spectrograph (STIS) in January 2004. Discrete emissions were detected, with some evidence of latitudinal variations of localized emissions and motions. At the same time, Cassini's Ultraviolet Imaging Spectrograph (UVIS) studied the intensity and spectral distribution of Saturn's northern night side emission region. With the benefit of simultaneous observations, we found that the characteristics of Saturn's emission region in the day side southern aurora appeared correlated with Saturn kilometric radio (SKR) emissions, charged particles and magnetic field measurements in the night side Saturn magnetosphere. The faint UV aurora are consistent with the previously reported correlation between radio and UV emissions, and the low disturbance in Saturn's magnetosphere observed by Cassini. In this quiet state, the auroral oval brightness is a few kilorayleighs (KR). The summed images show evidence of an offset auroral oval toward midnight responding to solar wind pressure and more diffuse features in the dusk side. The specific properties of Saturn's aurora in its minimum state will be presented, and compared with more active periods. [less ▲]

Detailed reference viewed: 18 (4 ULg)
See detailHST/GHRS ultraviolet spectroscopy and model diagnostics of the Jovian aurora.
Gérard, Jean-Claude ULg; Dols, V.; Gustin, Jacques ULg et al

in Bulletin of the American Astronomical Society (1999)

A model coupling a detailed synthetic spectrum of the H_2 Lyman and Werner band systems with an electron energy degradation code is applied to the analysis of 7 GHRS spectra of the 1200-1700 { Angstroms ... [more ▼]

A model coupling a detailed synthetic spectrum of the H_2 Lyman and Werner band systems with an electron energy degradation code is applied to the analysis of 7 GHRS spectra of the 1200-1700 { Angstroms} region obtained with a ~ 5 { Angstroms} resolution at various locations in the north and south Jovian aurora. The observed color ratios indicate that the characteristic energy of the assumed initial Maxwellian distribution ranges between 17 and 40 keV. A clear signature of acetylene is observed near the absorption peaks at 1520, 1480 and 1440 { Angstroms}. The C_2H_2 column overlying the emission peak varies from 0.02 to 0.2 of the methane column. A better fit is obtained for some spectra when ethane absorption is added. The changing mixing ratios relative to methane are attributed to perturbations by heat released by the fast electron thermalization and/or perturbations to the hydrocarbon chemistry resulting from the production of H atoms by the aurora. A spectrum of the Io magnetic footprint and its trailing tail shows ultraviolet color and hydrocarbon absorption charateristics quite similar to some of the main oval spectra. This observation implies that the electrons of the Io flux tube are energized to a few tens of keV, similar to the electron precipitated in the main ovals and polar caps. Echelle spectra between 1216 and 1220 { Angstroms} at 0.07 { Angstroms} resolution are also compared with the model best fitting the closely spaced in time mid-resolution spectrum. It is found that the effective H_2 rovibrational temperature associated with the Echelle spectra is significantly higher than predicted by the model. A steep temperature gradient near the methane homopause due to large heating by auroral precipitation is a plausible explanation for this difference. We acknowledge funding by NASA and the PRODEX program of the European Space Agency. [less ▲]

Detailed reference viewed: 21 (8 ULg)
See detailHST/STIS images of UV auroral footprints from Io, Europa, and Ganymede.
Clarke, J. T.; Ajello, J.; Ballester, G. E. et al

in Bulletin of the American Astronomical Society (1999)

Ultraviolet images of Jupiter's aurora have been obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) since September 1997 with much higher sensitivity than ... [more ▼]

Ultraviolet images of Jupiter's aurora have been obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) since September 1997 with much higher sensitivity than earlier cameras. Higher sensitivity permits shorter exposures, freezing Jupiter's rotation and providing the highest angular resolution obtained to date. This combination of sensitivity and resolution has revealed new emissions from the magnetic footprints of Io, Europa, and Ganymede, which will be reported and discussed. Io's auroral footprint, while well studied with earlier cameras, appears highly extended at a low brightness in the wake or plasma flow direction. Ganymede's auroral footprint emission is now well established from the repeated appearance of this feature under the magnetic field trace of Ganymede, and there is initial evidence for auroral emission at Europa's magnetic footprint. Ganymede's auroral footprint appears consistently equatorward of the main auroral oval, which clearly constrains the main oval auroral currents to originate from beyond about 20 R_J. The observation that the main oval emissions are observed to corotate with Jupiter's magnetic field further constrains the origin of these currents to be within about 30 R_J, so that the source region for the main oval auroral is now fairly well constrained to a region in Jupiter's middle magnetosphere and within the current sheet. This work was supported by NASA under grant GO-7308.01-96A to the University of Michigan. [less ▲]

Detailed reference viewed: 25 (9 ULg)