1 / 10

Variations of the auroral UV emission from Io’s atmosphere

Variations of the auroral UV emission from Io’s atmosphere . Lorenz Roth * J. Saur * , P.D. Feldman, D.F. Strobel , K.D. Retherford * Institute of Geophysics University of Cologne, Germany. Observations of Io´s auroral emission. HST / STIS UV 135.6 nm Roesler et al., 1999.

urbano
Download Presentation

Variations of the auroral UV emission from Io’s atmosphere

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Variations ofthe auroral UV emissionfrom Io’s atmosphere Lorenz Roth*J. Saur*, P.D. Feldman, D.F. Strobel, K.D. Retherford *Institute of GeophysicsUniversity of Cologne, Germany

  2. ObservationsofIo´sauroralemission HST / STIS UV 135.6 nm Roesler et al., 1999 Galileo SSI visible – 3 filters 380 - 710 nm Geissler et al., 1999 Cassini ISS near UV – blue visiblered Geissler et al., 2004 New HorizonsLORRI visible- UV 350 - 850 nm Roth et al., 2011

  3. Generation of Io’s aurora • ExcitationofIo´satmospherebyelectronimpact • Atmosphericproperties:- columndensityofN≈ (1-5)∙1016 cm-2 (sunlit) (Lellouch et al., 2007)- mainconstituent: SO2
- various minor components: O, O2, S, S2, SO, Na, K, Cl, NaCl • Electrons in theplasmatorus:- thermal electrons: kTe= 5 eVne = 1200-3600 cm-3- non-thermal electrons: kTe≈ keV • The auroraastoolto find propertiesof:- atmosphericdistribution, compositionanddensity- plasmaconditions- magneticfieldconfiguration

  4. HST / STIS observationsofIo´s UV aurora 50 exposuresduring 26 orbitsbetween1997 and 2001 2 exposures in eclipse 40 exposurescontainingOI 1356 Åemission- the clearest of emissions imaged 19 combinedobservationimages(2 exposuresduringoneorbit) ➩ 2 x better signal-to-noiseratio (afterRetherford, 2002)

  5. MorphologyoftheOI 1356 Åemission • Morphologyonlydependson the: • 1. observinggeometry 2. tiltofthebackgroundfield • 3. positionwithrespecttothetorus

  6. Model ofthe 3D emissiondistribution • Goal: Find a simple functionthatisabletodescribethe 3D emissionprofilearoundIofor all STIS observationswithasfewparametersaspossible • Main aurorafeatures:- Equatorialspots- backgroundemission- limbglow (north- southdifferences) • Constructionof 2D modelimagesbyintegratingalongline-of-sight • Comparisonbetweenmodelimagesand 18 combinedSTIS OI 1356 Åobservations (Io in sunlight)

  7. Aurora model • Background emission: • Emission on theflanks(equatorialspots): • Rotatethe 3D profileintothe B fieldcoordinatesystem➩ Tiltdeterminedby • Brightness proportional todistancetotoruscenter ( ) • 13 fit parameters (in red) • 6 areas: - off-disk emission / on-disk emission - anti-Jovian spot / sub-Jovian spot (9x9 pixels) - limbglow North / South + positionoftheequatorialspots • Find least squaresfor all 18 observations:

  8. Observations - Model

  9. Results Aurora modelisabletoreproducethemainfeaturesofthemorphologyobservedover 5 years(1997 – 2001) Tiltofaurora ~ 80% oftiltofbackgroundfield Spots:- longitudinal extension: ∼22°- spotcentershifteddownstreamfrom sub-/ anti-jovianmeridian: ~12° / ~4°- Distanceofcentertosurface: ~ 50 km- brightnessesandextensionssimilar! Eclipseobservation:- faintestemissionof all STIS observations- but: also faintestmodeledemission- sub-Jovian spotappearssmallerandfurtherupstream

  10. Summary • Weexamined 18 HST/STIS observationsofthe OI 1356 ÅemissionfromIo`satmospheretakenbetween 1997 and 2001 • Assumption: Morphologyofthe OI 1356 Åauroraonlydepends on the:1. observationgeometry2. tiltofthebackgroundfield3. positionofIowithrespecttothetorus • Weestablished a phenomenologicalmodelforthe3D emissiondistributionaroundIothatreproducestheobservedauroramorphology. • Onlyweakvariationsofthe3D emissionprofilebetween 1997 and 2001. ➩ Comparisonsofother (new) observationswiththeauroramodel (Roth et al., Simulation of Io’s auroralemission…, Icarus, available online)

More Related