SOT observing modes for local helioseismology and data
SOT observing modes for local helioseismology and data analysis Takashi Sekii NAOJ SOT 17, Tokyo
SOT and local helioseismology o SOT provides high-resolution Dopplergrams and thus a great opportunity to study subsurface structure and flow (and a lot more) n Spatial resolution 0. 2” = 150 km@disc centre SOT 17, Tokyo 2
High resolution powerspectrum o MDI high-resolution power spectrum n n No resonant p modes above ℓ≈2000 The f-mode frequency ∝ sqrt(ℓ) SOT 17, Tokyo 3
High resolution t-d diagram o Sekii et al 2001: MDI(left) versus La Palma SVST G-band (right, Berger et al 1998) SOT 17, Tokyo 4
How do we use SOT for local helioseismology? (1/2) o Which line(s)? n Fe I 5576 (non-magnetic, photosphere) o o o Field of view n o Mg I 5173 (magnetic, chromosphere) One of magnetic iron lines the full unvignetted field: 240”x 160” 2 x 2 summing: OK except (perhaps) at high latitudes SOT 17, Tokyo 5
How do we use SOT for local helioseismology? (2/2) o Cadence n 1 min is the “standard” o o 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 SOT 17, Tokyo 6
Data amount aspect o A 12 -hr run of single-line observation, 320”x 160” FOV, 2 x 2 summing, 1 -min cadance, JPEG compression → ~9 Gbits SOT 17, Tokyo 7
Data analysis (1/3) o 1. 2. 3. 4. 5. Time-distance analysis Calibrated & tracked Dopplergrams n wavefield characterization, excitation study、surface flow etc Filtered Dopplergrams (phasespeed filter, averaging on segments etc) Cross-covariance function Travel-time measurement Inversion for subsurface structure & flow SOT 17, Tokyo 8
Data Analysis (2/3) o Inversion: Ray approximation kernels for p-mode waves + MCD inversion n How shall we incorporate f-mode data? More sophisticated/realistic methods? It is still a developing subject SOT 17, Tokyo 9
Data analysis (3/3) o o Most of the scientific targets are achieved by the standard t-d analysis and its by-products We may add n n o “Simultaneous” observations with SP Multi-line observation for chromospheric waves Observation with a photospheric magnetic line (see the next slide) SOT 17, Tokyo 10
The first thing we would like to do o A joint observation with MDI SOT field in the middle of MDI field QT & AR n n n 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 SOT 17, Tokyo 11
Time-distance analysis in ARs o Doppler measurement based on FGs n n n o 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 n n Scattering, changes in thermal structure, suppressed excitation Richard Wachter’s talk SOT 17, Tokyo 12
Summary o o High-resolution local-helioseismology by SOT Time-distance inversion at the centre of the analysis SOT 17, Tokyo 13
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