Finally I captured a series of spectra concerning the space around the volcanic satellite with the aim to detect envelope shape. For this purpose I used a graduated reticle on slit-view camera field (shown in the image) by moving jupiter satellite on several notches of the grid perpendicular to slit and taking the spectrum.
Using an image editing tool, I superimposed every preprocessed 2d Na emission line "slice" on slit-view image with Jupiter and satellites, respecting the scale by means of graduations (I taken some Io spectra moving it on notches along slit for calculate the ratio of scale between the slit-view/spectrum cameras).
So, this is the result:
Jupiter-Io direction is not aligned with dispersion because of strong Jupiter glare (along dispersion) that contaminate the cloud spectrum. Note I had to change the visualization thresholds of 2d spectra that are closer to the planet because of glow that raise sky background. So I think Na emission in the space toward the planet could be really more noticeable. The notches of the grid in the field are separated by 12 arcsec, about 40.000 Km at Jupiter distance.
Image show that the sodium cloud (detected with this setup) is not distributed spherically around the satellite but stretches along its orbital plane, with some asymmetries. So, in this 115 degree eastern phase angle, the cloud show an elongated shape. This should be in line with astronomer's model. Long (but faint) Na emission lines far away from Jupiter suggest the sodium envelope is very large and surround the entire galileian moons system. It would be interesting to take the spectra with a greater exposure than 12 minutes used for this work.
These are the native 2d spectrum I used:
Hope that I have done things well... Anyway, I have not discovered anything but it seems incredible to me what we can do today with amateur equipment!
Ciao,
Paolo