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Spatial deconvolution and inversion of 2D spectropolarimetric data. Asensio Ramos Ruiz Cobo Instituto de Astrofísica de Canarias. The Earth atmosphere strongly perturbs the ability to get good images and polarimetric data.
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Spatialdeconvolutionand inversion of 2D spectropolarimetricdata • Asensio Ramos • Ruiz Cobo • Instituto de Astrofísica de Canarias
TheEarthatmospherestronglyperturbstheabilityto getgoodimages and polarimetric data
Buteventhediffraction at thetelescopemodifiestheobservations
Motivation Develop a fastmethodtoinvertspatiallydeconvolved spectro-polarimetricobservationsfromspace
Imagedeconvolution Imageformation in a linear system Imagedeconvolution as a probabilisticproblem ForGaussiannoise Richardson-Lucy algorithm (Richardson 1972, Lucy 1974)
Problemswithimagedeconvolution • Spectropolarimetric data has to be deconvolvedfrequencybyfrequency • Thesignal-to-noise ratio in manyfrequenciesisverysmall • Maximum-likelihooddeconvolutionisverysensitivetonoise • Use a prior forimagestodiminishtheeffect of noise
Our prior forthesignal Wewritethe Stokes profiles as a linear combination in anorthonormalbasis Thelinearity of theimageformation leads to Projectingonthebasis and usingtheorthonormality of thebasis, the deconvolution reduces todeconvolvingseveral ‘projectedimages’
Original Deconvolved
Original Deconvolved
Advantages • Projectedimages are almostnoiseless, so thatthemaximum-likelihooddeconvolutionbehavesmuchbetter • Ifthebasis set issufficiently general, no relevantinformationislost inthetruncation we use anempirical PCA basis • Thedeconvolutionprocessiscomputationally simple, unlikeotherapproacheslikethat of van Noort (2012) • Nowanyinversionscheme can be appliedwithoutstray-light correction
Thecontrast in thequietregionsincreases fromfrom 6.3% to11.7%
Deconvolved Original
Penumbra – Magneto-convection in inclinedmagneticfield? • MHD simulations reproduce penumbra as magneto-convection in inclinedmagneticfielc (Rempel et al. 2009 a,b) • Downwardvelocitieswithinversepolaritiesshould be observedalongtheborders of penumbralfilaments • Convectivedownflow Scharmer et al. (2011), Scharmer & Henriqes (2012), Joshi et al. (2011) • Reversed flux in outer penumbra Westendorp Plaza et al. (1997,2001)del Toro Iniesta et al. 2001 • Indirectindications in Stokes V Franz (2011)
Afterdeconvolution Beforedeconvolution (2-component inversion)
Conclusions • Fastregularizareddeconvolutionavailable • Dispersed light almostdisappears • Inversion of 2D data • Clear signatures of downflowing material withoppositepolarity in the penumbra