[en] This study reports the analysis of far ultraviolet (FUV) limb spectra of the airglow of Saturn in the 1150–1850 Å spectral window, obtained with the Ultraviolet Imaging Spectrograph (UVIS) onboard Cassini, spanning altitudes from 1200 to 4000 km. The FUV limb emission consists of three main contributions: (1) H Ly-a peaking at 1100 km with a brightness of 0.8 kilo-Rayleighs (kR), (2) reflected sunlight longward of 1550 Å which maximizes at 950 km with 16.5 kR and (3) H2 bands in the 1150–1650 Å bandwidth, peaking at 1050 km reaching a maximum of 3.9 kR.
A vertical profile of the local H2 volume emission rate has been derived using the hydrocarbon density profiles from a model of the Saturn equatorial atmosphere. It is well matched by a Chapman function, characterized by a maximum value of 3.5 photons cm-3 s-1 in the 800–1650 Å UV bandwidth, peaking at 1020 km.
Comparisons between the observed spectra and a first-order synthetic airglow H2 model in the 1150–1650 Å bandwidth show that the spectral shape of the H2 bands is accounted for by solar fluorescence and photoelectron excitation. The best fits are obtained with a combination of H2 fluorescence lines and 20 eV electron impact spectra, the latter contributing 68% of the total H2 airglow emission.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Gustin, Jacques ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Stewart, Ian; Laboratory for Atmospheric and Space Physics > Colorado University
Gérard, Jean-Claude ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Esposito, Larry; Laboratory for Atmospheric and Space Physics > Colorado University
Language :
English
Title :
Characteristics of Saturn’s FUV airglow from limb-viewing spectra obtained with Cassini-UVIS
Publication date :
2010
Journal title :
Icarus
ISSN :
0019-1035
eISSN :
1090-2643
Publisher :
Academic Press, San Diego, United States - California
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