{"id":"pod_polito_vanessa_2021-05-24T16:29:42.339Z","submitter":"(2) Rosseland Centre for Solar Physics, University of Oslo, P.O.Box 1029 Blindern, NO-0315 Oslo, Norway","author":"Sargam M. Mulay (1) and Lyndsay Fletcher (1,2)","status":"published","creation-date":"2021-05-24T16:29:42.344Z","last-modified-date":"2021-07-12T23:20:47.314Z","credit":"(1) School of Physics & Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK","title":"Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite","contentBlocks":[{"type":"text","text":"In%20this%20study%2C%20we%20observe%20molecular%20hydrogen%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%201333.79%20%26Aring%3B%20emission%20at%20the%20flare%20ribbons%20during%20different%20phases%20of%20the%20M7.3%20class%20solar%20flare%20observed%20by%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%3B%20De%20Pontieu%20et%20al.%202014%29%20on%20April%2018%2C%202014.%20The%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20line%20has%20a%20formation%20temperature%20of%204200%20K%20%28Innes%202008%29%20and%20its%20emission%20is%20produced%20through%20the%20photo-excitation%20%28fluorescence%29%20process%20by%20ultraviolet%20%28UV%29%20radiation%20from%20the%20IRIS%20Si%20IV%201402.77%20%26Aring%3B%20line.%20This%20work%20provides%20a%20unique%20view%20and%20plasma%20properties%20of%20the%20temperature%20minimum%20region%20%28TMR%29.%20High-resolution%20IRIS%20observations%20allow%20us%20to%20study%20the%20behavior%20and%20plasma%20properties%20of%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20emission%20at%20the%20flare%20ribbons%20during%20various%20phases%20of%20the%20flare%2C%20the%20correlation%20between%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20the%20Si%20IV%20emission%2C%20and%20the%20optical%20properties%20of%20the%20plasma%20to%20the%20outward-going%20radiation%2C%20using%20the%20ratio%20of%20the%20two%20Si%20IV%20line%20intensities."},{"type":"image","file":"","url":"nuggetvideos/2021/05/24/pod_polito_vanessa_2021-05-24T16%3A29%3A42.339Z/Selection_698.png","hash":"515b3773b7ff3819609695d5a1ae3658","mimeType":"image/png","caption":"Figure%201%20-Left%20panel%3A%20GOES%20X-ray%20fluxes%20and%20their%20derivative%20for%20an%20M7.3%20flare.%20The%20plasma%20parameters%20from%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20were%20obtained%20for%20the%20time%20slot%20marked%20by%20dashed%20lines.%20Right%20panel%3A%20The%20southern%20flare%20ribbon%20is%20observed%20in%20the%20IRIS%20SJI%20Si%20IV%20filter.%20The%20two%20regions%20of%20a%20southern%20flare%20ribbon%20are%20labeled%20as%20Ribbon%201%20%28R1%29%20and%202%20%28R2%29."},{"type":"text","text":"Emission%20from%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20were%20observed%20throughout%20the%20flare%20evolution.%20At%20R1%2C%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20was%20visible%20only%20when%20emission%20from%20Si%20IV%20was%20bright.%20We%20observed%20that%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20emission%20is%20strongest%20during%20the%20flare%20impulsive%20phase%2C%20dims%20during%20the%20GOES%20peak%2C%20and%20brightens%20again%20during%20the%20gradual%20phase.%20At%20R2%2C%20the%20Si%20IV%20emission%20was%20strong%20but%20at%20the%20same%20time%20and%20location%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20line%20was%20faint.%20This%20might%20be%20caused%20by%20the%20fact%20that%20the%20opacity%20of%20the%20chromosphere%20at%20the%20R2%20location%20was%20higher%20than%20that%20at%20the%20R1%20location.%20We%20noted%20that%20R1%20crosses%20a%20plage%20region%2C%20whereas%20R2%20crosses%20a%20spot%20penumbra%2C%20which%20is%20expected%20to%20have%20different%20temperature%2C%20density%20and%20hence%2C%20opacity%20structures."},{"type":"image","file":"","url":"nuggetvideos/2021/05/24/pod_polito_vanessa_2021-05-24T16%3A29%3A42.339Z/Selection_683.png","hash":"1cd5433cfece7fd95eb1a7ec66663e8e","mimeType":"image/png","caption":"Figure%202%20%E2%80%93%20Left%20and%20middle%20panels%20%E2%80%93%20%28a%29%20%26amp%3B%20%28d%29%20spectral%20images%20created%20by%20summing%20the%20intensities%20over%20the%20range%20of%20wavelengths%201333.76%20-%201333.87%20%26Aring%3B%2C%20and%201402.5%20-%201403.6%20%26Aring%3B.%20%28b%29%20%26amp%3B%20%28e%29%20spectral%20images%20formed%20at%20the%20single%20%28peak%29%20wavelength%20for%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines.%20Right%20panel%3A%20Example%20spectra%20of%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20along%20with%20Gaussian%20fit%20components."},{"type":"text","text":"The%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20were%20broad%20%28see%20Fig.%202%2C%20right%20panel%29.%20We%20measured%20non-thermal%20speeds%20in%20the%20range%20of%207-18%20km%2Fs%20in%20the%20molecular%20line%2C%20whereas%20its%20Doppler%20shifts%20were%20consistent%20with%20zero%20within%20the%20errors%2C%20indicating%20negligible%20bulk%20flows%20along%20the%20line-of-sight.%0AWe%20studied%20the%20correlation%20between%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20emission%20by%20plotting%20the%20light%20curves%20for%20both%20ribbons.%20For%20R1%2C%20the%20overall%20pattern%20of%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20intensity%20variation%20is%20very%20similar%20to%20that%20of%20Si%20IV%20and%20showed%20many%20of%20the%20same%20small-scale%20features.%20For%20R2%2C%20there%20is%20little%20small-scale%20intensity%20variation%20in%20both%20Si%20IV%20and%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20.%20The%20scatter%20plots%20for%20the%20total%20intensities%20of%20the%20lines%20showed%20a%20strong%20positive%20correlation.%20The%20correlation%20coefficient%20for%20both%20ribbons%20is%20of%20the%20same%20order%20of%20magnitude%2C%20but%20the%20gradient%20differs%20by%2050%25.%20We%20obtained%20a%20shallower%20gradient%20for%20the%20R2."},{"type":"image","file":"","url":"nuggetvideos/2021/05/24/pod_polito_vanessa_2021-05-24T16%3A29%3A42.339Z/Selection_678.png","hash":"ea80b65b30904f87aae3b3e6f7b2abdf","mimeType":"image/png","caption":"Figure%203%20%E2%80%93%20Left%20panel%20%E2%80%93%20the%20light%20curves%20for%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20lines%20at%20the%20two%20ribbon%20locations.%20Right%20panel%3A%20Scatter%20plots%20for%20the%20total%20intensity%20of%20Si%20IV%20and%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D."},{"type":"image","file":"","url":"nuggetvideos/2021/05/24/pod_polito_vanessa_2021-05-24T16%3A29%3A42.339Z/Selection_679.png","hash":"e362653aab1ae45fba8605c59475d863","mimeType":"image/png","caption":"Figure%204%20-%20%28a%29%20%26amp%3B%20%28b%29%20spectral%20images%20created%20by%20summing%20the%20intensities%20over%20the%20range%20of%20wavelengths%201393.5%20-%201394.6%20%26Aring%3B%2C%20and%201402.5%20-%201403.6%20%26Aring%3B.%20Middle%20panel%3A%20Si%20IV%20ratio%20map%20along%20with%20Si%20IV%20contours.%20The%20dark%20blue%20patches%20indicate%20saturated%20spectra.%20Right%20panel%3A%20Histograms%20of%20the%20pixel%20numbers%20in%20R1%20and%20R2%20indicating%20the%20Si%20IV%20line%20ratios."},{"type":"text","text":"From%20the%20ratio%20of%20Si%20IV%20%281393.76%2F1402.77%29%2C%20we%20deduce%20that%20the%20plasma%20is%20optically%20thin%20to%20Si%20IV%20%28where%20the%20ratio%20%3D%202%29%20during%20the%20impulsive%20phase%20of%20the%20flare%20in%20locations%20where%20strong%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20emission%20was%20observed.%20In%20contrast%2C%20the%20ratio%20differs%20from%20the%20optically%20thin%20value%20of%202%20in%20parts%20of%20ribbons%2C%20indicating%20a%20role%20for%20opacity%20effects.%0A%0AConclusions%3A%0A%20%20%20%E2%80%A2%20We%20observed%20a%20strong%20spatial%20and%20temporal%20correlation%20between%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20and%20Si%20IV%20emission%2C%20suggesting%20that%20the%20%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20emission%20is%20produced%20by%20fluorescent%20excitation%20from%20Si%20IV.%0A%20%20%E2%80%A2%20Although%20the%20Doppler%20shifts%20were%20consistent%20with%20zero%2C%20the%20%5Cbegin%7Bequation%7DH_2%5Cend%7Bequation%7D%20line%20was%20broad%20and%20the%20non-thermal%20speeds%20were%20in%20the%20range%20of%207-18%20km%2Fs.%0A%20%20%E2%80%A2%20IRIS%20observations%20provide%20useful%20constraints%20for%20further%20modeling%20of%20the%20chromosphere%20and%20TMR%20during%20flares."}],"references":["<a 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