In this report the parameters of temperature, column density and total emission of the molecular ion H3+ were obtained from spectra of the Jovian aurorae. The spectra were obtained using the SpeX spectrograph, which gave a spatial resolution of 0.15” per pixel, giving some of the best spatial resolution of the aurora obtained to date. These parameters were used to obtain profiles across the aurorae and were combined to produce maps to try and show how the parameters varied. The temperature was shown to vary between ~ 900-1100K, the column density between ~ 5-15*1016 m-2, and the total emission between 1-4*10-3 Wm-2. The parameters were found to be in general agreement with others studies conducted over the past decade or so.
The northern aurora was studied in more detail than the southern one, due to more of it being visible. One particular profile showed the variation across the aurora in most detail. This profile showed that the main region of energy deposition in the aurora was in the main oval, corresponding to magnetospheric connection to somewhere between 12 – 30 RJ on the plasmasheet. The correspondence between the column density and emission showed that energy was being deposited in the same place as it was emitted, meaning that H3+ emission can be used as an accurate probe of where particle precipitation is occurring. The correspondence between temperature and emission showed that H3+ acts as a major cooling mechanism within the aurora. The dark polar region was shown to have significant emission compared with that from the main body of the planet, with particle precipitation possibly from the solar wind. Various regions, like the bright polar region where precipitation come from greater than 30 RJ, were shown to have not easily explicable anomalies in the parameters e.g. large peaks in temperature and emission with a minimum in column density or vice versa. One possible explanations for these anomalies was speculated as there being transport of particles within the aurora, providing localised heating, cooling or spreading effects, via neutral or ion winds, with a candidate for the ion wind being the auroral electrojet. Another possible explanation put forward was for precipitation of particles to occur at different altitudes within the aurora, whereby at higher altitudes the temperature is greater but the density is less. This would be explained by particles of different energy precipitating from different distances out on the plasmasheet, via different current systems. Whether or not, mechanisms such as the electrojet can be used to explain the transport of H3+ or energy to lower latitudes, thus explaining the anomalous temperatures there, is beyond the scope of these results.
The maps showed that the aurora was an area in which higher precipitation occurred than the rest of the planet, due to the falling off of all the parameters at their edges. The temperature was shown to be the least variable of the parameters. The column density and emission maps correlated well, but did not provide a very complete view of the main regions of energy deposition.
Improvements and future work
In this study there are several areas that could be improved upon with more time. As was stated in the report, several of the spectra seemed to contain an anomalous amount of off planet points. The reason for these would need to be investigated further, with the possibilities of errors in the position finding being explored more thoroughly, along with more detailed calculations of the actual dimensions of Jupiter being made (i.e. its diameter to the top of the ionosphere). From this, more accurate values of longitude and latitude could be produced, which would fit the aurora to the sphere at a more realistic latitude. Something that was not included in the calculations in this report was the fact that Jupiter had a 3° tilt towards Earth at the time of observation, which would need to be taken into account for more accurate maps (although it was not considered to make a major enough difference to the result to merit the extra time it would have taken in calculating for this study). With a more accurate map it would have been worth projecting calculated equipotential magnetic field lines onto them, which would provide far better knowledge of where the features originate from in the magnetosphere. Due to the maps produced in this study being too low in latitude there was not much point in trying to link up features and equipotentials to such accuracy, and therefore any quoted in this study are from previous estimates. The fact that the spectrometer slit was moved across the aurorae during to observations, to try and cover the aurora as fully as possible, and orientated in a north-south direction, to get both aurora at once, provided the biggest complication to calculation longitudes and latitudes, and probably added to errors in position. In the future it would probably be wise to keep the slit positioned on the CML to minimise positional errors.
The observations used in this report were only from one night in a series, which will all have to be analysed. Hopefully what has been learnt in this study will prove useful in that task, and that some of the above issues will be addressed.
The study of Jupiter’s aurorae, ionosphere and magnetosphere via H3+ spectroscopy, is continuing at pace, with more observations having been made very recently. These hope to probe conditions even more accurately, with continued look at energy transport mechanisms within the ionosphere and its links with the magnetosphere. Studies of H3+ on the other gas giants are also being pursued, to learn more about their upper atmospheres.
I would like to thank my supervisors Dr Steve Miller and Dr Tom Stallard for giving me such an interesting project on which to work, and wish them well in there continuing studies of H3+ on Jupiter and other Gas Giants. Special thanks go to Tom for all his help in answering my questions and helping with IDL queries. I would also like to thank all of the APL staff for letting me in when needed. All my friends to whom I have complained to, moaned at and generally bored with talk about the project also deserve a mention, especially the two who help me prepare my talk.
Ballester, G. E. Miller, S. Tennyson, J. Trafton, L. M. Geballe, T. R, Icarus, 107, 189-194 (1994)
Baron, R. L. Owen, T. Connerney, J. E. P. Satoh, T. Harrington, J, Solar wind control of Jupiter’s H3+ auroras, Icarus, 120, 437-442 (1996)
Drossart, P. Maillard, J. –P. Caldwell, J. Kim, S. J. Watson, J. K. G. Majewski, W. A. Tennyson, J. Miller, S. Atreya, S. K. Clarke, J. T. Waite Jr, J. H. Wagener, R, Detection of H3+ on Jupiter, Nature, 340, pp. 539-541 (1989)
Lam, H. A. Achilleos, N. Miller, S. Tennyson, J. Trafton, L. M. Geballe, T. R. Ballester, G. E, A baseline spectroscopic study of the infrared auroras of Jupiter, Icarus, 127, 379-393 (1997)
Miller, S. Joseph, R. D. Tennyson, J, Infrared emissions of H3+ in the atmosphere of Jupiter in the 2.1 and 4.0 micron region, Astrophys. J., 360, L55-L58 (1990)
Miller, S. and Tennyson, J, H3+ in space, Chem. Soc. Reviews, 281-288 (1992)
Miller, S. Achilleos, N. Ballester, G. E. Lam, H. A. Tennyson, J. Geballe, T. R. Trafton, L. M, Mid-to-low latitude H3+ emission from Jupiter, Icarus, 130, 57-67 (1997)
Miller, S. Achilleos, N. Ballester, G. E. Geballe, T. R. Joseph, R. D. Prangé, R. Rego, D. Stallard, T. Tennyson, J. Trafton, L. M. Waite Jr, J. H, Phil. Trans. R. Soc. Lond., 358, 2485-2502 (2000)
Oka, T. and Geballe, T. R, Observations of the 4 micron fundamental band of H3+ in Jupiter, Astrophys. J., 351, L53-L56 (1990)
Rego, D. Miller, S. Achilleos, N. Prangé, R. Joseph, R. D, Latitudinal profiles of the Jovian IR emissions of H3+ at 4mm with the NASA Infrared Telescope Facility: Energy inputs and thermal balance, Icarus, 147, 366-385 (2000)
Rogers, J. H, The Giant Planet Jupiter, Cambridge University Press (1995)
Satoh, T. Connerney, J. E. P, Jupiter’s H3+ emissions viewed in corrected Jovimagnetic coordinates, Icarus, 141, 236-252 (1999)
Stallard, T. S, Dynamical studies of the Jovian ionosphere, Ph.D. Thesis, University of London (2001)
NASA IRTF SpeX
Appendix A: List of programs
- fitted theoretical spectrum with observed spectrum to produce values of temperature, column density and total emission
- calibrated spectrum, defined auroral regions, obtained positional information, called the two procedures directly below
- cut down arrays to include only the needed lines, passed information into spexbak5, read out parameters and positional information to files.
- produced plots of the fitted and observed spectrum, with and without background
- produced the line of sight corrections for latitude and longitude
- converted positional information from pixel numbers to latitudes and longitudes on Jupiter
- called the above three procedures to do them all together
- put data into map arrays and interpolated between points, called interp_lat.pro to interpolate between latitude points
- put north and south maps together into map over all latitudes and longitudes, and projected them onto spherical surface
- created profiles of different parameters, or combinations of parameters
Example of FORTRAN code
C Version of November 07, 2001
C This program is designed to fit IRTF SpeX 3 to 4 micron spectra *
C to high level emissions from H3+ and a background consisting of *
C a scaled value of the background fitted from low latitude spectra. *
C For H3+ it fits the temperature of the emitting region, and the *
C number density, and combines these to give the total emission. *
C It uses the NAG routine E04FDF. Fortran source is included. *
IMPLICIT DOUBLE PRECISION (A-H,O-Y), LOGICAL (Z)
DIMENSION X(4), W(200000)
COMMON /SPEC1/ F(4000), FOH3P(4000), FPH3P(4000), WL(4000),
1 AOH3P(500), APH3P(500), WOH3P(500), WPH3P(500),
2 WUOH3P(500), WUPH3P(500), WT(4000), CSPEC, CDENS,
COMMON /SPEC3/ DWL, E0, ITIME
COMMON /SPEC4/ NTRANO, NTRANP, JOH3P(500), JPH3P(500), WMID
C BEAM converts the derived column density for a pixel area of *
C 1 arsec square. It has to be reduced if the pixel is larger. *
C Read in of title
1 5X,'Program SPEXBAK5, version of November 07, 2001',/,/)
READ(5,*) DWL, DL, E0, PIXAREA, CSPEC, CDENS
WRITE(7,*) DWL, DL, E0, PIXAREA, CSPEC, CDENS
Example of IDL code
;;This is a procedure for the bottom
aurora (left and right), to work out
;;the temperature, column density and total emissivity
;;The left side
;;I am only going to look at the Q branch to get the best fit
;;need to make it loop through all
the columns (sleft) of data
;;for the entire region selected
for j=0, (sleft-1) do begin
openw, 1, 'fort.1'
for i=0, leftrows-505 do begin
printf, 1, wavelength1(i), array1(i)
openw, 1, 'fort.11'
for i=0, leftrows-505 do begin
printf, 1, wavelength1(i), methleftarr(i)
spawn, 'spexbak5 <data1'
;;need to read in temp, column density
and total emissivty for
;;each position across the auroral region