Time-resolved observations of Jupiter's far-ultraviolet aurora

Science

Volumn 274, Issue 5286, 1996, Pages 409-413

  Ballester, Gilda E ^a   Clarke, John T ^a   Trauger, John T ^b   Harris, Walter M ^c   Stapelfeldt, Karl R ^b   Crisp, David ^b   Evans, Robin W ^b   Burgh, Eric B ^d   Burrows, Christopher J ^d   Casertano, Stefano ^e   Gallagher III, John S ^c   Griffiths, Richard E ^d   Hester, J Jeff ^f   Hoessel, John G ^c   Holtzman, Jon A ^g   Krist, John E ^e   Meadows, Vikki ^b   Mould, Jeremy R ^h   Sahai, Raghvendra ^b   Scowen, Paul A ^f   Watson, Alan M ^g   Westphal, James A ⁱ   more..

^a UNIVERSITY OF MICHIGAN   (United States)

^b CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^c UNIVERSITY OF WISCONSIN MADISON   (United States)

^d JOHNS HOPKINS UNIVERSITY   (United States)

^e STScI   (United States)

^f ARIZONA STATE UNIVERSITY   (United States)

^g NEW MEXICO STATE UNIVERSITY   (United States)

^h AUSTRALIAN NATIONAL UNIVERSITY   (Australia)

ⁱ CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ASTRONOMY; ATMOSPHERE; GEOMETRY; IMAGING SYSTEM; MAGNETIC FIELD; PLASMA; PRIORITY JOURNAL; SPACE; ULTRAVIOLET SPECTROPHOTOMETRY;

EID: 0012663823     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5286.409     Document Type: Article

References (44)

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27. The 20 July 1994 WFPC2 images spanned CMLs ∼104° to 181° [Fig. 3, G and F (6)], and the 18 July 1994 image had a CML of 171° [Fig. 3E (6)]; the poleward offset should not be related to auroral events, since events did not occur during the 16 to 23 July 1994 comet Shoemaker/Levy 9 impact into Jupiter [(6); S. A. Budzien et al., Bull. Am. Astron. Soc. 27, 1149 (1995); S. Miller et al., Geophys. Res. Lett. 22, 1629 (1995)].
28. The 20 July 1994 WFPC2 images spanned CMLs ∼104° to 181° [Fig. 3, G and F (6)], and the 18 July 1994 image had a CML of 171° [Fig. 3E (6)]; the poleward offset should not be related to auroral events, since events did not occur during the 16 to 23 July 1994 comet Shoemaker/Levy 9 impact into Jupiter [(6); S. A. Budzien et al., Bull. Am. Astron. Soc. 27, 1149 (1995); S. Miller et al., Geophys. Res. Lett. 22, 1629 (1995)].
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31. I. Engle, J. Geophys. Res. 97, 17169 (1992), shows the north cusp boundary latitudinally displaced by ∼5° from the magnetic axis for CML 202°, when the magnetic dipole axis is inclined toward Earth by 10° from the rotational axis.
32. Fluxes in the 1200 to 1230, 1230 to 1300, 1300 to 1550, and 1550 to 1620 Å intervals were derived following W. M. Harris, J. T. Clarke, M. A. McGrath, G. E. Ballester, Icarus, in press.
33. The IUE telescope has a nominal 3-arc sec Gaussian PSF [A. Boggess et al., Nature, 275, 377 (1978)]. We used a conservative 3.5 arc sec FWHM, and found similar results with 4.0 arc sec.
34. The disk-reflected sunlight was subtracted by using the fluxes integrated inside the IUE aperture in the convolved F16OBW + F165LP images, scaled to the F160BW images by comparing average counts at the equator. The F160BW + F165LP images of orbits 1 and 5 differ somewhat at the poles, so a linear interpolation was made before subtraction.
35. A similar conclusion was reached by R. Prangé et al. (J. Geophys. Res., in press) based on a set of FOC-IUE observations. In this WFPC2-IUE study, the photometry and morphology are more accurately compared because of WFPC2's higher sensitivity to low-level emissions.
36. The north/south peak emission ratio was about 3, but this includes large geometric effects.
37. R. Prangé et al., J. Geophys. Res. 98, 18779 (1993).
38. J. C. Gérard et al., Science 266, 1675 (1994).
39. W. M. Harris et al., Bull. Am. Astron. Soc. 27, 1149 (1995).
40. The event emission appeared to lag co-rotation since at CMLs of 141°, 149°, 190°, 200°, and 208°, the peak north emission was around λ ∼ 210°, 210°, 228°, 227°, and 231°, respectively. The magnetic dawn footprint was at λ ∼ 190°, 193°, 225°, 236°, and 245°, respectively. For the July 1993 event imaged by FOC (20), the reported quasi co-rotation included the increase of the leading emission edge and, at the imaged CMLs 108° to 172°, reflected the motion of the dawn footprint.
41. Low dispersion IUE exposures consisted of 110 spatial lines of spectra, with the aperture's long axis nearly perpendicular to dispersion. After camera noise and grating-scattered light subtraction (14), a 30 × 30 pseudo-image was extracted at 1216 Å. The centering of the aperture was uncertain by about one IUE pixel (∼ 1 arc sec or ∼1.2 Å), and was adjusted by tracing the aperture's edge with the extended geocoronal and Jupiter's disk-reflected H-Lyα background emissions.
42. Although the north dawn auroral sector falls inside the IUE aperture for CMLs of ∼120° to 360° to 20° given the IUE pointing, after a CML of 270° the main oval starts to set behind the limb. Around a CML of 20° it rises again, but the dawn sector falls outside the aperture, so IUE always observes maximum event emission around CMLs of ∼150° to 270° (2, 79, 21).
43. -1, the ram pressure was about average, and there were no significant magnetic field perturbations. The ballistic projection was confirmed (within ~∼1 day) with magnetometer data from the Galileo Orbiter. On May 1994, Galileo was ∼1.7 AU from Jupiter at a ∼17° Jupiter-sun-Galileo angle, and did not detect any magnetic field perturbations that could have reached Jupiter on ∼28 to 31 May 1994 [K. Khurana, private communication (1996)].
44. We are grateful to A. Storrs at the Space Telescope Science Institute (STScl) for his efforts in scheduling these WFPC2 GTO observations and to B. McCollum and the IUE staff at Goddard Space Flight Center for scheduling and execution of the IUE observations on short notice G.E.B. is also grateful to I. Engle, F. Bagenal, L. Ben Jaffel, R. Thorne, D. Rego, R. Clauer, and A. Ridley for helpful conversations; K. Khurana for providing the Galileo data; and the referees for helpful suggestions. This research was supported by the Jet Propulsion Laboratory 959122 and NASAADP NAG5-3044 grants to the University of Michigan. This work was based on observations with the NASA-European Space Agency HST, obtained at the STScl, which is operated by the Association of Universities for Research in Astronomy for NASA under contract NAS5-26555.