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Guo Y.,Observatoire de Paris | Guo Y.,Nanjing University | Schmieder B.,Observatoire de Paris | Bommier V.,Observatoire de Paris | Gosain S.,Udaipur Solar Observatory
Solar Physics | Year: 2010

The main objective of this paper is to build and compare vector magnetic maps obtained by two spectral polarimeters, i.e. THEMIS/MTR and Hinode SOT/SP, using two inversion codes (UNNOFIT and MELANIE) based on the Milne - Eddington solar atmosphere model. To this end, we used observations of a facular region within active region NOAA 10996 on 23 May 2008, and found consistent results concerning the field strength, azimuth and inclination distributions. Because SOT/SP is free from the seeing effect and has better spatial resolution, we were able to resolve small magnetic polarities with sizes of 1″ to 2″, and we could detect strong horizontal magnetic fields, which converge or diverge in negative or positive facular polarities. These findings support models which suggest the existence of small vertical flux tube bundles in faculae. A new method is proposed to get the relative formation heights of the multi-lines observed by MTR assuming the validity of a flux tube model for the faculae. We found that the Fe I 6302.5 Å line forms at a greater atmospheric height than the Fe I 5250.2 Å line. © 2010 Springer Science+Business Media B.V. Source

Gosain S.,Udaipur Solar Observatory | Schmieder B.,Observatoire de Paris
Annales Geophysicae | Year: 2010

The STEREO mission has been providing stereoscopic view of the filament eruptions in EUV wavelengths. The most extended view during filament eruptions is seen in He II 304 Å observations, as the filament spine appears darker and sharper. The projected filament width appears differently when viewed from different angles by STEREO satellites. Here, we present a method for estimating the width and inclination of the filament sheet using He II 304 Å observations by STEREO-A and B satellites from the two viewpoints. The width of the filament sheet, when measured from its feet to its apex, gives estimate of filament height above the chromosphere. © 2010 Author(s). Source

Artzner G.,Institute dAstrophysique Spatiale | Gosain S.,Udaipur Solar Observatory | Schmieder B.,Observatoire de Paris
Solar Physics | Year: 2010

The STEREO mission has been providing a stereoscopic view of filament eruptions in the EUV. The clearest view during a filament eruption is seen in He ii 304 Å observations. One of the main problems in visualizing filament dynamics in He ii 304 Å is the strong background contrast due to surface features. We present a technique that removes background features and leaves behind only the filamentary structure, as seen by STEREO-A and -B. The technique uses a pair of STEREO He ii 304 Å images observed simultaneously. The STEREO-B image is geometrically transformed to a STEREO-A view so that the background images appear similar. Filaments, being elevated structures, i. e., not lying on the same spherical surface as background features, do not appear similar in the transformed view. Thus, subtracting the two images cancels the background but leaves behind the filament structure. We apply this technique to study the dynamics of the filament-eruption event of 22 May 2008, which was observed by STEREO and followed by several ground-based observatories participating in the Joint Observing Programme (JOP 178). © Springer Science+Business Media B.V. 2010. Source

Schmieder B.,Observatoire de Paris | Demoulin P.,Observatoire de Paris | Pariat E.,Observatoire de Paris | Torok T.,Observatoire de Paris | And 10 more authors.
Advances in Space Research | Year: 2011

During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst = -457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared. © 2010 Published by Elsevier Ltd. on behalf of COSPAR. Source

Sankarasubrmanian K.,Space Astronomy Group | Gosain S.,Udaipur Solar Observatory | Venkatakrishnan P.,Udaipur Solar Observatory | Bayanna A.R.,Udaipur Solar Observatory
Journal of Optics (India) | Year: 2012

A novel solar spectroscopic concept by combining a Shack-Hartmann (SH) and a Fabry- Perot (FP) interferometer is being developed to obtain high cadence solar observations of active as well as quiet regions. SH is used to generate multiple images of the same field-of-view (FOV) of interest. Whereas FP is used to tune these multiple images for different central wavelengths thus obtaining different points on the spectral line profiles in a single exposure. Initial laboratory simulation of such a configuration provides the proof of concept. With a 10×10 lenslet array and with a suitable combination of collimating and imaging lenses, a wavelength shift of ∼1 A was achieved. © 2012 Optical Society of India. Source

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