Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011a%26a...530a.139b&link_type=abstract
Astronomy & Astrophysics, Volume 530, id.A139
Astronomy and Astrophysics
Astrophysics
1
Polarization, Molecular Data, Planets And Satellites: Aurorae, Planets And Satellites: Individual: Jupiter
Scientific paper
Context. Measurement of linear polarisation in Earth's thermospheric oxygen red line can be a useful observable quantity for characterising conditions in the upper atmosphere; therefore, polarimetry measurements are extended to other planets. Since FUV emissions are not observable from the ground, the best candidates for Jupiter auroral emissions are H3+ infrared lines near 4 μm. This ion is created after a chemical process in the Jovian upper atmosphere. Thus the anisotropy responsible of the polarisation cannot be the particle impact as in the Earth case. Aims: The goal of this study is to detect polarisation of H3+ emissions from Jupiter's aurora. Methods: Measurements of the H3+ emissions from Jupiter's southern auroral oval were performed at the UK Infrared Telescope using the UIST-IRPOL spectro-polarimeter, with the instrument slit positioned perpendicular to Jupiter's rotation axis. Data were processed by dividing the slit into 24 bins. Stokes parameters (u, q and v), polarisation degree and direction were extracted for each bin and debiased. Results: More than 5 bins show polarisation with a confidence level above 3σ. Polarisation degrees up to 7% are detected. Assuming the auroral intensity is constant during the 8 waveplate positions exposure time, i.e. around 10 min, strong circular polarisation is present, with an absolute value of the Stokes v parameter up to 0.35. Conclusions: This study shows that polarisation is detectable in the Jovian infrared auroras, but new measurements are needed to be able to use it to characterise the ionospheric environment. At present, it is not possible to propose a mechanism to explain this polarisation owing to the lack of theoretical work and laboratory experiments concerning the polarisation of H3+ .
Barthelemy Marc
Lilensten Jean
Lystrup Makenzie B.
Menager Hélène
Miller Samantha
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