IRIS Nugget
Welcome to the IRIS Science Nuggets: highlights of recent IRIS scientific results for the solar physics community.
{"id":"pod_polito_vanessa_2022-10-25T17:48:34.066Z","submitter":"Dr. Yamini K. Rao","author":"Yamini K. Rao, Giulio Del Zanna, Helen E. Mason, and Roger Dufresne","status":"published","creation-date":"2022-10-25T17:48:34.071Z","last-modified-date":"2022-11-15T18:54:50.799Z","credit":"DAMTP, University of Cambridge, Wilberforce Rd, Cambridge CB3 0WA, United Kingdom","title":"Path length studies in the solar transition region using IRIS","contentBlocks":[{"type":"text","text":"Mass%20and%20energy%20are%20transferred%20from%20the%20lower%20atmosphere%20to%20the%20corona%20through%20the%20transition%20region.%20An%20understanding%20of%20the%20dynamical%20processes%20in%20the%20transition%20region%20could%20be%20complemented%20by%20studies%20about%20path%20lengths%20and%20filling%20factors%20%28Del%20Zanna%20and%20Mason%2C%202018%29.%20The%20path%20lengths%2C%20%20%5Cbegin%7Bequation%7Ddh%5Cend%7Bequation%7D%2C%20are%20generally%20obtained%20from%20intensities%20and%20densities%20measured%20from%20spectral%20lines%20and%20can%20be%20approximated%20by%20the%20following%20formula%3A%0A%0A%5Cbegin%7Bequation%7D%0AI%3DG%28T%29N_e%5E2dh%0A%5Cend%7Bequation%7D%0A%0Awhere%20%5Cbegin%7Bequation%7DG%28T%29%5Cend%7Bequation%7D%20is%20the%20peak%20value%20of%20the%20contribution%20function%2C%20%5Cbegin%7Bequation%7DN_e%5Cend%7Bequation%7D%20is%20the%20electron%20density%2C%20and%20%5Cbegin%7Bequation%7Ddh%5Cend%7Bequation%7D%20is%20the%20path%20length.%20The%20path%20lengths%20give%20a%20line-of-sight%20measure%20of%20the%20thickness%20of%20the%20transition%20region%20plasma%20at%20%5Cbegin%7Bequation%7D10%5E5%5Cend%7Bequation%7D%20K.%20In%20our%20present%20work%2C%20we%20conduct%20a%20detailed%20study%20from%20the%20Interface%20Region%20Imaging%20Spectrograph%20%28IRIS%29.%20We%20also%20revisit%20earlier%20observations%20including%20SUMER%20and%20HRTS%2C%20and%20the%20results%20from%20Dere%20et%20al.%20%281987%29%2C%20where%20they%20reported%20path%20lengths%20in%20the%20range%20of%200.1%20to%2010%20km%20using%20HRTS%20observations%2C%20assuming%20a%20similar%20formation%20temperature%20for%20C%20IV%20and%20O%20IV.%20We%20have%20used%20the%20weaker%20O%20IV%20lines%20to%20estimate%20electron%20densities%20and%20the%20path-lengths%20with%20IRIS%2C%20using%20a%20similar%20method.%20However%2C%20we%20have%20made%20certain%20improvements.%20The%20improved%20CHIANTI%20model%20now%20includes%20density%20effects%2C%20photo-ionization%2C%20and%20charge%20transfer%20%28Dufresne%20et%20al.%2C%202021a%2C%202021b%29.%0A%0AFig.%201%20shows%20a%20comparison%20of%20the%20contribution%20functions%20of%20lines%20from%20O%20IV%2C%20S%20IV%2C%20and%20Si%20IV%20at%20a%20constant%20pressure%20of%203%20%26times%3B%20%20%5Cbegin%7Bequation%7D10%5E%7B14%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D%20K%20using%20CHIANTI%20and%20the%20improved%20ionization%20equilibrium%20model.%20The%20solid%20lines%20represent%20the%20contribution%20functions%20of%20different%20ions%20using%20the%20improved%20ionization%20equilibrium%20while%20the%20dashed%20lines%20represent%20CHIANTI%20values%20with%20zero-density%20effects."},{"type":"image","file":"","url":"nuggetvideos/2022/10/25/pod_polito_vanessa_2022-10-25T17%3A48%3A34.066Z/Screen 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Shot 2022-11-14 at 12.49.29 PM.png","hash":"edc30ffe47ce7b8947f5aa1346dba160","mimeType":"image/png","caption":"Fig%202%3A%20The%20estimation%20of%20path%20lengths%20for%20the%20QS%20near%20the%20disc%20centre%20observed%20on%2022nd%20October%202013%20with%20an%20exposure%20time%20of%2030s.%20Top-left%20panel%20shows%20the%20ratios%20of%20the%20radiance%20of%20the%20O%20IV%201404%2F1401%20%26Aring%3B%20lines.%20Top-right%20panel%20shows%20the%20densities%20derived%20from%20the%20O%20IV%20ratio%20values.%20Bottom-left%20panel%20indicates%20the%20temperature%20calculated%20by%20the%20O%20IV%201401%2FS%20IV%201406%20%26Aring%3B%20line%20ratios.%20Bottom-right%20panel%20shows%20the%20path%20lengths%20estimated%20using%20densities%20from%20the%20O%20IV%20lines%20and%20considering%20an%20isothermal%20formation%20temperature%20of%20O%20IV%20at%20log%20T%5BK%5D%20%3D%205.1."},{"type":"image","file":"","url":"nuggetvideos/2022/10/25/pod_polito_vanessa_2022-10-25T17%3A48%3A34.066Z/Screenshot 2022-11-10 at 10.54.01 AM.png","hash":"14c6269fe31c05e9a87d3a609b984553","mimeType":"image/png","caption":"Fig.%203%3A%20The%20estimation%20of%20path%20lengths%20for%20the%20QS%20close%20to%20the%20limb%20observed%20on%2022nd%20January%202014%20with%20an%20exposure%20time%20of%2015s.%20Top-left%20panel%20shows%20the%20ratios%20of%20the%20radiance%20of%20O%20IV%201401%2F1401%20%26Aring%3B%20lines.%20Top-right%20panel%20shows%20the%20densities%20derived%20from%20O%20IV%20ratio%20values.%20Bottom-left%20panel%20indicates%20the%20temperature%20calculated%20by%20O%20IV%201401%2FS%20IV%201406%20%26Aring%3B%20line%20ratios.%20Bottom-right%20panel%20shows%20the%20path%20lengths%20estimated%20by%20using%20densities%20from%20the%20O%20IV%20lines%20and%20considering%20an%20isothermal%20formation%20temperature%20of%20O%20IV%20at%20log%20T%20%5BK%5D%20%3D%205.1."},{"type":"text","text":"We%20observe%20that%20the%20density-sensitive%20O%20IV%20lines%20provide%20typical%20averaged%20densities%20around%20%5Cbegin%7Bequation%7D10%5E%7B10%7D%20cm%5E%7B-3%7D%5Cend%7Bequation%7D.These%20values%20were%20found%20to%20be%20consistent%20with%20the%20values%20reported%20in%20earlier%20publications%20using%20different%20instruments.%20We%20assessed%20the%20effects%20of%20the%20new%20atomic%20models%20on%20the%20results.%20We%20found%20centre-to-limb%20variations%20of%20path%20lengths.%20The%20median%20value%20is%20observed%20to%20be%2010%20km%20near%20the%20disc-centre%20while%20it%20increases%20to%2031%20km%20for%20the%20limb%20dataset.%20These%20values%20are%20higher%20than%20those%20reported%20in%20Dere%20et%20al.%20%281987%29.%20The%20discrepancies%20can%20be%20attributed%20to%20various%20factors%20like%20the%20assumed%20abundances.%20We%20also%20show%20that%20performing%20an%20emission%20measure%20analysis%20lowers%20significantly%20the%20path%20lengths.%20A%20centre-to-limb%20variation%20in%20the%20non-thermal%20widths%20was%20also%20observed%20with%20IRIS%20%28Rao%20et%20al.%2C%202022%29.%20Thanks%20to%20the%20high-resolution%20of%20data%20from%20IRIS%2C%20we%20were%20able%20to%20make%20direct%20calculations%20of%20path%20lengths%20in%20the%20quiet-Sun%20transition%20region%20using%20OIV.%20Such%20small%20path%20lengths%20should%20be%20taken%20into%20account%20when%20modelling%20the%20transition%20region.%20Observations%20from%20other%20instruments%20of%20small%20features%20in%20H%28alpha%29%20%2C%20Mg%20II%2C%20and%20Si%20IV%20show%20widths%20narrower%20than%202%27%27%2C%20%28De%20Pontieu%20et%20al.%2C%202021%29%2C%20indicating%20very%20small%20filling%20factors%20in%20the%20transition%20region."}],"references":["Dere K. P., Bartoe J. D. F., Brueckner G. E., Cook J. W., Socker D. G., 1987, Sol. Phys., 114, 223","Del Zanna G., Mason H. E., 2018, Living Reviews in Solar Physics, 15, 5","Dufresne R. P., Del Zanna G., Badnell N. R., 2021a, MNRAS, 503, 1976","Dufresne R. P., Del Zanna G., Storey P. J., 2021b, MNRAS, 505, 3968","De Pontieu B., et al., 2021, Sol. Phys., 296, 84","Rao et al., MNRAS, Volume 517, Issue 1, November 2022","","","",""],"pubDate":"2022-11-14T20:43:44.545Z"}