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Takashi Sekii NAOJ SOT observing modes for local helioseismology and data analysis
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SOT17, Tokyo2 SOT and local helioseismology SOT provides high-resolution Dopplergrams and thus a great opportunity to study subsurface structure and flow (and a lot more) Spatial resolution 0.2” = 150km@disc centre
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SOT17, Tokyo3 High resolution powerspectrum MDI high-resolution power spectrum No resonant p modes above ℓ≈2000 The f-mode frequency ∝ sqrt(ℓ)
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SOT17, Tokyo4 High resolution t-d diagram Sekii et al 2001: MDI(left) versus La Palma SVST G-band (right, Berger et al 1998)
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SOT17, Tokyo5 How do we use SOT for local helioseismology? (1/2) Which line(s)? Fe I 5576 (non-magnetic, photosphere) Mg I 5173 (magnetic, chromosphere) One of magnetic iron lines Field of view the full unvignetted field: 240”x160” 2x2 summing: OK except (perhaps) at high latitudes
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SOT17, Tokyo6 How do we use SOT for local helioseismology? (2/2) Cadence 1 min is the “standard” But there is no reason a higher cadence should hurt, except in terms of telemetry A higher cadence may be favoured in particular for chromospheric wave study
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SOT17, Tokyo7 Data amount aspect A 12-hr run of single-line observation, 320”x160” FOV, 2x2 summing, 1-min cadance, JPEG compression → ~9 Gbits
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SOT17, Tokyo8 Data analysis (1/3) Time-distance analysis 1.Calibrated & tracked Dopplergrams wavefield characterization, excitation study 、 surface flow etc 2.Filtered Dopplergrams (phasespeed filter, averaging on segments etc) 3.Cross-covariance function 4.Travel-time measurement 5.Inversion for subsurface structure & flow
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SOT17, Tokyo9 Data Analysis (2/3) Inversion: Ray approximation kernels for p-mode waves + MCD inversion How shall we incorporate f-mode data? More sophisticated/realistic methods? It is still a developing subject
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SOT17, Tokyo10 Data analysis (3/3) Most of the scientific targets are achieved by the standard t-d analysis and its by-products We may add “Simultaneous” observations with SP Multi-line observation for chromospheric waves Observation with a photospheric magnetic line (see the next slide)
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SOT17, Tokyo11 The first thing we would like to do A joint observation with MDI SOT field in the middle of MDI field QT & AR Calibration (Doppler measurement, plate scale) Combined data provides better depth coverage Insight for t-d analyses in AR, using both magnetic and non-magnetic lines
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SOT17, Tokyo12 Time-distance analysis in ARs Doppler measurement based on FGs MDI algorithm optimized for QT Does not affect SOT directly, since SOT can use a non-magnetic line Does affect MDI-SOT joint observation Oscillations in AR Scattering, changes in thermal structure, suppressed excitation Richard Wachter’s talk
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SOT17, Tokyo13 Summary High-resolution local-helioseismology by SOT Time-distance inversion at the centre of the analysis
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