References of "Ajello, J"
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See detailSaturn Auroral Movies from Cassini UVIS
Pryor, W. R.; Stewart, I.; Esposito, L. W. et al

in American Geophysical Union, Fall Meeting 2009 (2009, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007-2009 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting UVIS to obtain a number of short movies of the rotating auroral structures. Selected movies will be presented with geometric overlays and in polar projections. In some movies a cusp-like feature is present near noon inside the oval. One movie from 2008 day 201 shows parallel linear features on the day side almost at right angles to the main auroral oval that appear, then lengthen, separate in the middle, and then fade away. Other movies show similar cusp-related structures that resemble the letter "Q" where a dynamical feature at right angles to the oval moves away from the cusp region. The 2008 day 201 movie also shows one bright "polar flare" inside the oval with a spectrally distinct signature indicating the presence of higher energy electrons. A few of the most recent images were obtained at sufficiently close range that 2 spacecraft slews were needed to completely cover the oval. These images provide almost 100 pixels of information across the oval and clearly show multiple arcs of emission on the main oval and scattered emissions inside the oval. Several frames show emissions associated with the footprint of the Enceladus field line. We will discuss these features, their locations, and possible interpretations. [less ▲]

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See detailSaturn Auroral Movies from Cassini UVIS
Pryor, W. R.; Stewart, I.; Esposito, L. et al

Conference (2008, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed four years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed four years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2008 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting UVIS to obtain a number of short movies of the rotating auroral structures. In some movies a cusp-like feature is present near noon inside the oval. One movie from 2008 day 201 shows parallel linear features on the day side almost at right angles to the main auroral oval that appear, then lengthen, separate in the middle, and then fade away. The same movie also shows one bright "polar flare" inside the oval. A few of the most recent images were obtained at sufficiently close range that 2 spacecraft slews were needed to completely cover the oval. These images provide almost 100 pixels of information across the oval and clearly show multiple arcs of emission on the main oval and scattered emissions inside the oval. We will discuss these features, their locations, and possible interpretations. [less ▲]

Detailed reference viewed: 47 (2 ULg)
See detailAuroral Movies and Spectroscopy from Cassini UVIS
Pryor, W. R.; West, R.; Stewart, I. et al

Conference (2007, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting us to create images, spectra, and at times movies. We will present an auroral movie from 2007-145 that has been processed to remove flat-fielding artifacts and deconvolved to remove scattering along the slit. The movie shows near co- rotation of N polar auroral features with the planet's rotation. An auroral oval is present. The oval appears doubled on the midnight side. Other images from this year show emissions inside the auroral oval. We will discuss these images and their spectra. Additional images and movies are planned in coming months. [less ▲]

Detailed reference viewed: 36 (1 ULg)
See detailSaturn's Auroras and Polar Atmosphere from Cassini UVIS
Pryor, W. R.; West, R.; Larsen, K. et al

Conference (2006, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn, with sufficient spatial resolution to image Saturn's auroral oval when Cassini leaves Saturn's equatorial plane. We will present new images and time-series data from summer 2006. Detailed spectral models of molecular hydrogen auroral emissions that include hydrocarbon absorption and hydrogen self- absorption have now been compared to UVIS data. We are analyzing a UV spectral feature detected in an auroral oval image from 2005. The feature is an absorption feature concentrated inside the oval, at wavelengths dominated by reflected sunlight and acetylene absorption. The absorption feature appears as a broad absorption "scoop". One plausible molecule that has a similar absorption feature is benzene, which has a cross-section some 500 times larger than acetylene in this spectral region. Thus UVIS is sensitive to small quantities of benzene. Enhanced polar benzene has been previously observed at Jupiter and can be generated in coupled photochemical/auroral models. We will explore the uniqueness of this interpretation, and compare the inferred benzene abundances to results from complementary Cassini CIRS infrared observations. Additional out of the equatorial plane UVIS Saturn data planned for the coming months will improve the signal- to-noise ratio and spatial resolution on the auroral ovals and their interior. Coordinated observations with Cassini VIMS and Hubble Space Telescope are being scheduled for 2007. [less ▲]

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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 ▲]

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See detailObservations of Saturn's Atmosphere and Auroras by Cassini UVIS and VIMS
Pryor, W. R.; Baines, K.; West, R. et al

Conference (2005, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed a year of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed a year of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to build up spectral images of Saturn, with sufficient spatial resolution to reveal Saturn's auroral oval. Saturn images include evidence for rapid auroral variations and polar UV-dark regions mostly inside the auroral ovals. Absorption bands of acetylene are clearly seen in the reflected sunlight spectrum. The auroral emission spectrum is similar to that of Jupiter, showing H2 band emission and H Lyman-alpha emission. Saturn's auroral, dayglow, and nightglow spectra show significant differences. Saturn's aurora is observed to vary in brightness by at least a factor of four. The brightest auroral emissions seen so far occurred after 2004 day 207 19:30 when Cassini CAPS and MAG recorded passage of a solar wind shock. The enhanced auroral brightness persisted for days, and is seen at both poles of Saturn. Cassini RPWS observed enhanced auroral kilometric emissions during several auroral brightening events seen by UVIS. A campaign of Hubble Space Telescope UV imaging with ACS (Advanced Camera for Surveys) of Saturn's dayside southern auroral zone took place on 2005 February 17. Cassini UVIS and VIMS observed Saturn's nightside northern aurora during this period. The UVIS long slit was aligned with lines of latitude on Saturn, providing information about intensity and spectral variations along the auroral oval. Cassini VIMS has now obtained an initial image and spectrum of Saturn's H3}+ auroral emissions. [less ▲]

Detailed reference viewed: 32 (6 ULg)
See detailUltraviolet Spectroscopy of Saturn: Determination of Auroral characteristics with FUSE, STIS and UVIS Spectra
Gustin, Jacques ULg; Gérard, Jean-Claude ULg; Feldman, P. D. et al

Poster (2005, September 01)

Ultraviolet (UV) lines from Saturn's aurorae are emitted following inelastic collisions between energetic electrons and H[SUB]2[/SUB] molecules. De-excitation by radiative process lead to Far Ultraviolet ... [more ▼]

Ultraviolet (UV) lines from Saturn's aurorae are emitted following inelastic collisions between energetic electrons and H[SUB]2[/SUB] molecules. De-excitation by radiative process lead to Far Ultraviolet (FUV) and Extreme Ultraviolet (EUV) emissions in the 750-1750 Å spectral window. Low resolution spectra ( 12 Å) obtained with HST/STIS in the 900-1700 Å window are employed to derive the absorption of the auroral photons by hydrocarbons (mainly methane) and depth of the auroral energy deposition. Determination of H[SUB]2[/SUB] temperature and overlying H[SUB]2[/SUB] column is achieved by analyzing spectra obtained with the FUSE instrument ( 0.2 Å resolution with the LWRS aperture in the 900-1200 Å spectral window). Below 1100 Å, transitions connecting to the v" = 0 and 1 levels of ground-state H[SUB]2[/SUB] are partially or totally absorbed by ambient H[SUB]2[/SUB] (self-absorption). Comparisons between observed and synthetic spectra allow to derive the gaz temperature and the overlying H[SUB]2[/SUB] column, which is an indicator of the depth of the aurora, hence of the energy of the precipitated electrons. Auroral spectra of Saturn at 12 Å resolution were also obtained with Cassini's Ultraviolet Imaging Spectrograph (UVIS), both in the EUV and FUV spectral bands. While the spectral resolution of UVIS is too low to estimate temperatures, the coverage of the entire UV domain allows to determine the energy of precipitated particles through the quantification of the methane and molecular hydrogen columns. Results from observations with these three instruments are presented and compared in order to characterize the auroral atmosphere and auroral electrons precipitated from Saturn's magnetosphere. [less ▲]

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See detailUltraviolet Spectroscopy of Saturn: Determination of Auroral characteristics with FUSE, STIS and UVIS Spectra
Gustin, Jacques ULg; Gérard, Jean-Claude ULg; Feldman, P. D. et al

in Bulletin of the American Astronomical Society (2005, August 01)

Ultraviolet (UV) lines from Saturn's aurorae are emitted following inelastic collisions between energetic electrons and H[SUB]2[/SUB] molecules. De-excitation by radiative process lead to Far Ultraviolet ... [more ▼]

Ultraviolet (UV) lines from Saturn's aurorae are emitted following inelastic collisions between energetic electrons and H[SUB]2[/SUB] molecules. De-excitation by radiative process lead to Far Ultraviolet (FUV) and Extreme Ultraviolet (EUV) emissions in the 750-1750 Ã spectral window. Low resolution spectra ( 12 Ã ) obtained with HST/STIS in the 900-1700 Ã window are employed to derive the absorption of the auroral photons by hydrocarbons (mainly methane) and depth of the auroral energy deposition. Determination of H[SUB]2[/SUB] temperature and overlying H[SUB]2[/SUB] column is achieved by analyzing spectra obtained with the FUSE instrument ( 0.2 Ã resolution with the LWRS aperture in the 900-1200 Ã spectral window). Below 1100 Ã , transitions connecting to the v" = 0 and 1 levels of ground-state H[SUB]2[/SUB] are partially or totally absorbed by ambient H[SUB]2[/SUB] (self-absorption). Comparisons between observed and synthetic spectra allow to derive the gaz temperature and the overlying H[SUB]2[/SUB] column, which is an indicator of the depth of the aurora, hence of the energy of the precipitated electrons. Auroral spectra of Saturn at 12 Ã resolution were also obtained with Cassini's Ultraviolet Imaging Spectrograph (UVIS), both in the EUV and FUV spectral bands. While the spectral resolution of UVIS is too low to estimate temperatures, the coverage of the entire UV domain allows to determine the energy of precipitated particles through the quantification of the methane and molecular hydrogen columns. Results from observations with these three instruments are presented and compared in order to characterize the auroral atmosphere and auroral electrons precipitated from Saturn's magnetosphere. [less ▲]

Detailed reference viewed: 23 (3 ULg)
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See detailThe electron excited ultraviolet spectrum of HD: Cross sections and transition probabilities
Ajello, J.; Palle, P. V.; Abgrall, H. et al

in Astrophysical Journal Supplement Series (2005), 159(2), 314-330

We have analyzed the high-resolution ultraviolet (UV) emission spectrum of molecular deuterium hydride (HD) excited by electron impact at 100 eV under optically thin, single-scattering experimental ... [more ▼]

We have analyzed the high-resolution ultraviolet (UV) emission spectrum of molecular deuterium hydride (HD) excited by electron impact at 100 eV under optically thin, single-scattering experimental conditions. The high-resolution spectrum (FWHM = 160 m angstrom) spans the wavelength range from 900 to 1650 angstrom and contains the two Rydberg series of HD: (1)Sigma(u)(+) 1s sigma, np sigma(B, B', B '', n = 2, 3, 4) --> X (1)Sigma(g)(+) and (1)Pi(u)(+)1s sigma, np pi(C, D', D '', D '', n = 2, 3, 4, 5) --> X (1)Sigma(g)(+). A model spectrum of HD, based on newly calculated transition probabilities and line positions including rovibrational coupling for the strongest band systems, B 1 Sigma(u)(+)- X (1)Sigma(+)(g), B' (1)Sigma(u)(+)- X (1)Sigma(g)(+), C (1)Pi(u) - X (1)Sigma(g)(+), and D (1)Pi(u) X (1)Sigma(g)(+), is in excellent agreement with observed intensities. The cross sections for direct excitation at 100 eV of the B (1)Sigma(u)(+), B' (1)Sigma(u)(+), C (1)Pi(u), and D (1)Pi(u) states were derived from a model analysis of the experimental fluorescence spectrum to the ground state. The absolute cross section values for excitation to the B (1)Sigma(u)(+), B' (1)Sigma(u)(+), C (1)Pi(u), and D (1)Pi(u) states were found to be (2.57 +/- 0.26) x 10(-17), (0.22 +/- 0.06) x 10(-17), (2.54 +/- 0,25) x 10(-17), and (0.17 +/- 0.04) x 10(-17) cm(2), respectively. We have also determined the dissociative excitation cross sections at 100 eV for the emission of Ly alpha at 1216 angstrom and Ly beta at 1025 angstrom lines, which are (7.98 +/- 1.12) x 10(-18) and (0.40 +/- 0.10) x 10(-18) cm(2), respectively. The summed excitation function of the closely spaced pair of lines, H Ly alpha and D Ly alpha, resulting from dissociative excitation of HD, has been measured from the threshold to 800 eV and is analytically modeled with a semiempirical relation. The model cross sections are in good agreement with the corrected Ly alpha cross sections of Mohlmann et al. up to 2 keV. Based on measurements of H, D (2s) production cross section values by Mohlmann et al., the H, D (n = 2) cross section is estimated to be 1.6 x 10(-17) cm(2) at 100 eV. [less ▲]

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See detailCassini ultraviolet imaging spectrograph observations of Saturn's auroras
Pryor, W. R.; West, R.; Stewart, A. I. F. et al

Conference (2005, August)

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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 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: 23 (5 ULg)
See detailThe HST Campaign on Jupiter's Aurora during the Cassini Flyby
Clarke, J. T.; Grodent, Denis ULg; Waite, J. H. et al

Conference (2002, July 29)

Detailed reference viewed: 8 (4 ULg)
See detailHST Observations of Aurora from the Magnetic Footprints of Io, Ganymede, and Europa during the Millennium Campaign
Clarke, J. T.; Grodent, Denis ULg; Connerney, J. et al

in Bulletin of the American Astronomical Society (2001, November 01)

UV images of Jupiter's aurora obtained with the HST STIS instrument reveal much detail in the distribution of emissions from Io's magnetic footprint on Jupiter, including extended trails of emission in ... [more ▼]

UV images of Jupiter's aurora obtained with the HST STIS instrument reveal much detail in the distribution of emissions from Io's magnetic footprint on Jupiter, including extended trails of emission in the downstream direction. Emissions are also seen from the magnetic footprints of Ganymede and Europa, relatively much fainter and point-like in spatial extent. Knowledge of the statistical properties of these emissions, in terms of their locations and brightnesses, was greatly advanced in a comprehensive series of images obtained during the Millennium campaign in Dec. 2000 - Jan. 2001. These images provide sufficient spatial coverage to give a good indication of the auroral oval locations mapping to Io and Ganymede, and a few points mapping to Europa. The observed variations in footprint properties provide indications of the nature of the electrodynamic interactions of the satellites with Jupiter's magnetic field. These and other indicators also show the direction that magnetic field models should take to better describe Jupiter's internal magnetic field. Contributing evidence comes from the locus of footprint latitudes, and their deviations from the VIP4 model. The latitudinal distance between the Io and Ganymede footprint loci indicates variations in the local field strength, with larger separations corresponding to a weaker field. These separations, and the distance from and distortion of the main oval, indicate an anomalously weak field region in the north near 90[SUP]o[/SUP] longitude. This work has been supported by NASA in STScI grants GO-08171-97A and GO-08657-01A to the University of Michigan. [less ▲]

Detailed reference viewed: 22 (2 ULg)
See detailH[SUB]2[/SUB] temperature and self-absorption: analysis of Jovian auroral spectra obtained with the FUSE satellite
Gustin, Jacques ULg; Feldman, P. D.; Gérard, Jean-Claude ULg et al

in Bulletin of the American Astronomical Society (2001, November 01)

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30 ... [more ▼]

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30"x30" LWRS aperture. All observed features belong to the H[SUB]2[/SUB] transitions from the B, C, B', D, B" and D' electronic states to the ground-state. These emissions are excited by inelastic collisions of the primary and secondary auroral electrons with H[SUB]2[/SUB] molecules. The relative intensity distribution of the observed lines depends on the rotational temperature of the emitting layer and self-absorption. Below 1100 Ì· , the transitions leading to the v" = 0, 1 and 2 levels of ground-state are partially or totally absorbed by H[SUB]2[/SUB], giving indications about the vibrational H[SUB]2[/SUB] distribution and overlying column. After a validation with an unabsorbed and a self-absorbed laboratory spectrum obtained in controlled conditions (100K, 300 eV), this study compares the observations and synthetic spectra, generated by a code including the B, C and B', D, B" and D' Rydberg states. The rotational and vibrational H[SUB]2[/SUB] temperatures are determined as well as the overlying H[SUB]2[/SUB] column. The combination of these parameters is used to determine the depth of the auroral energy deposition. This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. French participants are supported by CNES. Financial support to U.S. participants has been provided by NASA contract NAS5-32985. [less ▲]

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See detailA dawn auroral storm on Jupiter: measurement of complex hydocarbons
Clarke, J. T.; Gladstone, R.; Pryor, W. et al

Conference (2000, December)

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See detailHST/STIS Observations of a Dawn Auroral Storm on Jupiter
Clarke, J. T.; Gladstone, R.; Pryor, W. et al

in Bulletin of the American Astronomical Society (2000, October 01)

The HST/STIS recorded a detailed time series of images and spectra of the UV emissions from a dawn auroral storm on Jupiter on 21 Sept. 1999. The images show complex and evolving fine structure in the ... [more ▼]

The HST/STIS recorded a detailed time series of images and spectra of the UV emissions from a dawn auroral storm on Jupiter on 21 Sept. 1999. The images show complex and evolving fine structure in the storm, while the emission center remained along the main oval and near dawn in magnetic local time. We serendipitously recorded low resolution UV spectra of the north-south spatial distribution of the auroral emissions. These spectra show far stronger hydrocarbon absorptions than observed in any previous auroral spectra. This indicates an unusually deep penetration of the incident primary particles with respect to the neutral atmosphere, and correspondingly high energy of the primary particles. We can thus use these spectra to identify many complex hydrocarbons in Jupiter's auroral atmosphere which are not normally measured in auroral spectra. These results will be presented along with model fits to the spectra derived both from fitting the observed hydrocarbon absorption features and from comparison with a photochemical model for the expected composition of the auroral atmosphere. This research has been supported by grant GO-8171.01-97A from the Space Telescope Science Institute to the University of Michigan. [less ▲]

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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: 27 (9 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 ▲]

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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 ▲]

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