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IRIS Mg II Observations and Non-LTE Modeling of Off-limb Spicules in a Solar Polar Coronal Hole  

Akiko Tei   Submitted: 2019-11-27 18:36

We investigated the off-limb spicules observed in the Mg II h and k lines by IRIS in a solar polar coronal hole. We analyzed the large dataset of obtained spectra to extract quantitative information about the line intensities, shifts, and widths. The observed Mg II line profiles are broad and double-peaked at lower altitudes, broad but flat-topped at middle altitudes, and narrow and single-peaked with the largest Doppler shifts at higher altitudes. We use 1D non-LTE vertical slab models (i.e. models which consider departures from Local Thermodynamic Equilibrium) in single-slab and multi-slab configurations to interpret the observations and to investigate how a superposition of spicules along the line of sight (LOS) affects the synthetic Mg II line profiles. The used multi-slab models are either static, i.e. without any LOS velocities, or assume randomly assigned LOS velocities of individual slabs, representing the spicule dynamics. We conducted such single-slab and multi-slab modeling for a broad set of model input parameters and showed the dependence of the Mg II line profiles on these parameters. We demonstrated that the observed line widths of the h and k line profiles are strongly affected by the presence of multiple spicules along the LOS. We later showed that the profiles obtained at higher altitudes can be reproduced by single-slab models representing individual spicules. We found that the multi-slab model with a random distribution of the LOS velocities ranging from -25 to 25 km s-1 can well reproduce the width and the shape of Mg II profiles observed at middle altitudes.

Authors: Akiko Tei, Stanislav Gunar, Petr Heinzel, Takenori J. Okamoto, Jiri Stepan, Sonja Jejcic, Kazunari Shibata
Projects: IRIS

Publication Status: Accepted in the Astrophysical Journal
Last Modified: 2019-12-04 11:27
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Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare  

Akiko Tei   Submitted: 2018-03-15 00:45

We performed coordinated observations of AR 12205, which produced a C-class flare on 2014 November 11, with the Interface Region Imaging Spectrograph (IRIS) and the Domeless Solar Telescope (DST) at Hida Observatory. Using spectral data in the Si IV 1403 Å, C II 1335 Å, and Mg II h and k lines from IRIS and the Ca II K, Ca II 8542 Å, and Hα lines from DST, we investigated a moving flare kernel during the flare. In the Mg II h line, the leading edge of the flare kernel showed the intensity enhancement in the blue wing, and the smaller intensity of the blue-side peak (h2v) than that of the red-side one (h2r). The blueshift lasted for 9-48 s with a typical speed of 10.1 ± 2.6 km s-1 and it was followed by the high intensity and the large redshift with a speed of up to 51 km s-1 detected in the Mg II h line. The large redshift was a common property for all six lines but the blueshift prior to it was found only in the Mg II lines. A cloud modeling of the Mg II h line suggests that the blue wing enhancement with such peak difference can be caused by a chromospheric-temperature (cool) upflow. We discuss a scenario in which an upflow of cool plasma is lifted up by expanding hot plasma owing to the deep penetration of non-thermal electrons into the chromosphere. Furthermore, we found that the blueshift persisted without any subsequent redshift in the leading edge of the flare kernel during its decaying phase. The cause of such long-lasting blueshift is also discussed.

Authors: Akiko Tei, Takahito Sakaue, Tekanori J. Okamoto, Tomoko Kawate, Petr Heinzel, Satoru Ueno, Ayumi Asai, Kiyoshi Ichimoto, Kazunari Shibata
Projects: Fermi/GBM,GOES X-rays,IRIS,Nobeyama Radioheliograph,Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in PASJ
Last Modified: 2018-03-16 13:37
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IRIS Mg II Observations and Non-LTE Modeling of Off-limb Spicules in a Solar Polar Coronal Hole
Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare

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