Notes and caveats

Notes and caveats

Needs for a specific data processing :

For some purposes concerning a limited set of observations, several improvements of the standard systematic data processing pipeline can be performed on demand :
- A semi-automatic fitting routine was systematically applied to retrieve the planet’s exact position and pixel coordinates. Afterwards, a numerical background was subtracted to re-centered images before to proceed to cylindrical and to polar projections. More accurate centering and/or background models can be built case by case.
- STIS observations with long exposure times were most of the time acquired with the time-tag mode (see the detailed informations given by the search interface). This mode records the arrival time of each photon and provides the possibility to build sub-exposures over chosen intervals. Example : Long exposure time-tagged images of Jupiter acquired in 2009 were sequenced in 21x100s long images each.
- In a near future, APIS aims at providing the total radiated and precipitated hemispheric power for each image. Such estimates can already be done on restricted regions of interest (cusps, spots).
- 1D spectra were built from simple occurrence levels applied to the original 2D spectrum. 1D spectra of specific features (auroral arcs, satellite spots/wakes etc.) can be derived case by case.

The case of Saturn and Jupiter :

The header of Saturn and Jupiter (and their moons) processed fits files contains supplementary informations as :
- Saturn’s southern and northern SKR phases (source : Lamy, PRE7, 2011), available online.
- the position of main moons and the ephemeris of the Cassini and Galileo spacecraft (source : University of Iowa, Observatoire de Meudon).

The projections of Saturn’s images display additional specific features : white boxes in cylindrical projections indicate the expected footprint of Enceladus, and dashed-dotted (dashed) lines in polar projections indicate southern (northern) reference rotating meridians derived from the southern (northern) SKR phase system.

The projections of Jupiter’s images display markers at the footprint of the 4 galilean satellites : the arrows with decreasing thickness/length and increasing gray tone respectively indicate the footprint of Io, Europa, Ganymede and Callisto. These footprints have been modelled with the ISAaC - In-Situ and Auroral Contraints - magnetic field model (update of VIPAL, improved with the fitting of the Ganymede footprint, Hess, private communication). Supplementary magnetic boundaries of interest, such as the footprints of flux tubes crossing a constant distance at the equator, can be added on demand.

Imaging units :

We chose to display projected images in brightnesses (kilo-rayleighs, or kR) of total H2 emission over 80-170nm. Many past studies (e.g. GĂ©rard et al., 2004, 2005, 2006 ; Grodent et al., 2001, 2003, 2005 ; Clarke et al., 2005, 2009 ; Lamy, 2008 ; Bonfond, 2010) have performed successive photometric calibrations of STIS and ACS/SBC with typical auroral spectra to convert instrumental units (counts/s) into physical brigthnesses. The derived obtained conversion factors yielded significant disparities, owing to the considered radiative species (H2 and/or H-Lya), the consideration of absorption by hydrocarbons and the selected bandpass (spectral domain of H2 emission, FUV domain or bandpass restricted to that of HST imaging filters), as discussed by (Gustin et al., 2012 et Lamy et al., 2013). Here, we used the most recent estimates of (Gustin et al., 2012) derived for the two broad filters of each instrument (with color ratios of 2.5, 1.1 and 1.04 for Jupiter, Saturn and Uranus respectively), that we completed for the other employed filters. The conversion factors of filters concerning wavelengths mainly beyond the spectrum of H2, as F165LP for ACS, were set to 0.

The case of moons :

Although fitted with ellipsoids as for the images of planets (the pixel coordinates are available within the fits files of processed data), the images of moons were neither projected nor converted into auroral kR, owing to the lack of reliable conversion factors.

STIS irregular dark current :

Recent STIS observations may suffer a significant dark current on the FUV-MAMA detector that varies unpredictably in intensity. This results in an extended glow contaminating in particular the top left quadrant of the MAMA detector. No specific processing is applied to account for this sporadic dark current (source : STSci STIS handbook).