Takashi Sekii NAOJ SOT observing modes for local helioseismology and data analysis

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” = centre

SOT17, Tokyo3 High resolution powerspectrum  MDI high-resolution power spectrum No resonant p modes above ℓ≈2000 The f-mode frequency ∝ sqrt(ℓ)

SOT17, Tokyo4 High resolution t-d diagram  Sekii et al 2001: MDI(left) versus La Palma SVST G-band (right, Berger et al 1998)

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

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

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

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

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

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)

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

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

SOT17, Tokyo13 Summary  High-resolution local-helioseismology by SOT  Time-distance inversion at the centre of the analysis