observational study of ca ii k and mg ii h/k line ... · of ca ii k is not much different from that...
TRANSCRIPT
Observational study of Ca II K and Mg II h/k line formations in various solar conditions
Tomoko Kawate (Queen’s University Belfast), Kiyoshi Ichimoto (Kyoto U.), Satoru UeNo (Kyoto U.), Ken’ichi Otsuji (NAOJ), Tetsu Anan (Kyoto U.), Akiko Tei (Kyoto U.), Takahito Sakaue (Kyoto U.)
3. line intensity
Discussions and Conclusions
Analyses and Results
Abstract We performed a spectroscopic observation with Domeless Solar Telescope at Hida Observatory of Kyoto University in Japan. The obtained data are spectroheliogram in Ca II K, H-alpha and Ca II IR 8542 A of a plage region and flaring region, and simultaneously observed with IRIS Mg II h, k. Comparing the difference of spectral manifestations of Mg II h, k and Ca II K, we found a fairly good correlation between intensities of Ca II K and Mg II k. Their ratio is well understood by the Planck function as if they are emitted from layers at same temperature in active region, while Mg II get optically thick earlier in the quiet region and the eruptive filament. These differences can be explained by the opacity difference between Mg II h/k and Ca II K, which results from the difference of the abundances of these ions.
2. Imaging features
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Introduction
Fig.1 Formation height of Ca II and Mg II (Vernazza et al . 1981)
In a standard model, the formation height ���of Ca II K is not much different from that of Mg II h/k. We investigate the difference of the observational manifestations of Mg II and Ca II in order to understand what is the unique information provided by Mg II h/k lines over the Ca II H/K lines, and examine an important insight for designing future ���space missions like Solar-C.
From the spectra averaged spatially over plage/quiet/boundary region (divided with the white lines in Fig.6), we can see that K1 component in Ca II is large in the quiet region compared to Mg II k1, and relative red shift in the line core is rather smaller in Ca II K than Mg II.
Relationship between Ca K and Mg k intensities averaged over passbands of FWHM of K3, entire K2, region including K1, and region much affected by K1 are shown in Fig. 9 a - d, respectively. The red line in each panel shows that Mg k and Ca K are the same temperature (y ∝ x1.34). In the line core (Fig.9a and 9b), data fit well with the red line. On the other hand, the wider the passband gets, the steeper the inclination becomes than the red line, especially in low intensity region (= quiet region).
Fig.2 spectrogram of Ca II K and Mg II h/k
Fig.6 averaged spectra in plage / quiet / boundary region
Fig.9 intensity relationship between Ca K and Mg k
IRIS-4 WORKSHOP @Boulder, May 2015
In plage and flaring regions, intensities of Ca II K2, K3 and Mg II k2, k3 can be explained with optically thick with an unique temperature. However in quiet region or in the filament, the optically thick assumption is not valid any more and Ca II K gets optically thin. These results are reasonable considering opacity of Mg II k is much larger than Ca II K in solar atmosphere. From the results, we can conclude that Mg II is more powerful tool for studying faint features in upper chromosphere such as filaments, spicules and other small scale eruptions.
Observations
* Domeless Solar Telescope (DST)@ Hida Obs. - cadence: 0.05s /step, ~8s+dead time(~4s) /raster - spatial scale: 0.38”/pix, 0.68”/step - spectral scale: 0.0149 A/pix - Ca II K 3934, H-alpha 6563, Ca II 8542
* IRIS - Large sparse 64-step raster x 2 scan - cadence: 9.2s /step, 587s /raster - spatial scale: 0.33”/pix, 1.00”/step (NUV) - spectral scale: 0.051 A/pix (NUV)
Hida/DST HS CaII K 3934 15-Apr-2014 06:28:48.040 UT
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IRIS Mg II 2796 15-Apr-2014 06:19:09.440 UT
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(1) plage region Heliocentric angle: (236”,311”) Time: 2014-04-15 06:09-06:29 UT
CaK
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Fig.3 co-alignment of Ca II K2v and Mg II k2v (plage)
(2) flaring region (HOP 275) Heliocentric Angle: (120”,180”) Time: 2014-11-10 23:59-00:24(+1d) UT
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* DST@ Hida Obs. - cadence: 0.07s /step, ~8s+dead time(~2s) /raster - spatial scale: 0.26”/pix, 0.65”/step - spectral scale: 0.0149 A/pix - Ca II K 3934, H-alpha 6563, Ca II 8542
* IRIS - Large Sit-and-stare 0.3” x 120” - cadence: 9.5s - spatial scale: 0.33”/pix, 1.00”/step (NUV) - spectral scale: 0.051 A/pix (NUV)
After binning the spatial scale, we obtained spectra at the same position at the same time plage and quiet regions - 3571 spectra flaring active region - 7350 spectra
Fig.4 co-alignment of Ca II K and Mg II k sit-jaw (flare)
Theoretical aspect of Intensity Under optically thick conditions,
intensity is written by
If Ca II K (3933 A) and Mg II (2800 A) are formed at the same temperature layer, log IMg -log ICa relation will be given by a line whose slope is 1.34.
Fig.5 Intensity relationship under TCa = TMg
If the differential coefficient “d(log IMg)/d(log ICa) “ is larger than this value under assumption that τMg > τCa is always valid, it can be interpret as… - temperature of Ca K (@τCa=1) > temperature of Mg k (@τMg=1)
- both Mg k and Ca K lines get close to LTE - Ca K gets optically thin
In the sit-and-stare intensity map of Mg k3 and Ca K3, a filament eruption can be seen more clearly in Mg k3 than in Ca K3.
1. spectral features
The spectra averaged spatially over quiet/active/flaring region determined by the intensity around +/- 0.59 A of Ca K (which corresponds to 90 km/s) divided with the black/blue/green/red region are shown in Fig.7. We can see that, in red region (which mainly consists of flare kernels), the absorption in Mg k3 is almost disappeared while weak absorption still remains in Ca K3.
Fig.8 intensity map of flaring regions in sit-and-stare data
Fig.7 averaged spectra in quiet / active / flaring region
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flaring region plage region
Fig.10 line formation (Rutten 2003)
Fig.2 spectrogram of Ca II K and Mg II h/k
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(c) (d)
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IRIS SJI SDO 10-Nov-2014 23:59:21.170 UT
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IMg = A*ICa1.34
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