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##### Science From BiSON

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**Key Science Themes**• Structure of the Deep Radiative Interior • Sound Speed and Rotation • Origin and Influence of Solar Cycle • Origins of the Oscillations • Mode excitation and damping; surface physics • Solar Mean Magnetic Field (SMMF) …Roger New & Balazs Pinter**Achieving our Goals**• Specific Investigations • Many in collaboration • Lots of connectivity between investigations • Over-arching data preparation and analysis tasks**Over-arching Tasks**• Data calibration • Modelling/removal low-frequency footprint • Optimisation of data selection • Data preparation • Time series construction**Time series construction**Knitting a week of data together 10 hr 2 m/s Residual velocity (m/s) Time**Over-arching Tasks**• Data calibration • Modelling/removal low-frequency footprint • Optimisation of data selection • Data preparation • Time series construction • Gap filling • Public dissemination of data**Over-arching Tasks**• Mode parameter extraction • Development of fitting techniques**Changes Across the Mode Spectrum**Low Frequency High Frequency l=2/0 mode pairs in BiSON data**Over-arching Tasks**• Mode parameter extraction • Development of fitting techniques • Development and application of artificial data • Monte-Carlo applications vital for testing analysis(at all stages…)**Key Science Themes**• Structure of the Deep Radiative Interior • Origin and Influence of Solar Cycle • Origins of the Oscillations • Solar Mean Magnetic Field (SMMF)**Structure of the Deep Radiative Interior**• Sound speed and rotation profiles • New modes at low frequencies • More accurate frequency extraction • Removal of effects of surface layers, i.e., peak and multiplet asymmetry, solar-cycle shifts • Comparative/correlation analyses of different data vital**Origin and Influence of Solar Activity Cycle**• Study of mode parameter variations in greater detail • Dependence on angular degree, l Dependence on frequency • Careful comparison between datasets • What do differences between sets tell us? • Inform models of variations in mode properties**Origins of the Oscillations**• Mode excitation and damping • Using observation to inform models • Origin of large or unusual excitations: linking the interior to the surface • Tracking mode phase as an important tool**Origins of the Oscillations**• Surface Physics • Resonant peak asymmetry and phase shifts: influence of granulation • Height dependence in photosphere • SMMF**Solar Cycle Variations**Chaplin et al., in preparation Cycle 23 Cycle 22**Solar Cycle Variations**Howe et al., 2003, ApJ, 588, 1204 Frequency BiSON GONG Power density Linewidth**An Unusual Excitation that Bucks the Long-Term Trend**What was the cause? Chaplin et al., 2003, ApJ, L582, 115**Needles in a Haystack: Modes at Low Frequencies**Predicted 9 years of BiSON data**Low-Frequency p Modes**Chaplin et al., 2002, MNRAS, 336, 979**Importance of removal of surface activity**Inversion for sound speed with fractional radius 0.002 ...with ‘raw’ BiSON frequencies 0.001 -0.001 -0.002 0.2 0.4 0.6 0.8 1.0 Inversions courtesy A. Kosovichev**Importance of removal of surface activity**Inversion for sound speed with fractional radius 0.002 ...with ‘corrected’ BiSON frequencies 0.001 -0.001 -0.002 0.2 0.4 0.6 0.8 1.0 Inversions courtesy A. Kosovichev**Rotation Inversions**Effect of adding more low-l splittings at low frequency Artificial data: 400 nHz input**Low-Frequency p Modes**BiSON minus SACLAY model frequencies Chaplin et al., 2002, MNRAS, 336, 979**Frequency Uncertainties**Chaplin et al., 2002, MNRAS, 330, 731**Low-Frequency p Modes**GOLF minus BiSON frequencies Chaplin et al. 2002, 336, 979; Bertello et al., 2000a, b**Frequency Uncertainties Scale as T½**Perform analysis to find for model where errors scale as T Chaplin et al., 2002, MNRAS, 330, 731**Mode Lifetimes**Chaplin et al., 2002, MNRAS, 330, 731**High Frequency Spectrum**Solid: GOLF Dashed: BiSON**High-Frequency Peaks**GOLF blue wing minus BiSON**Low-Resolution BiSON Spectrum**Gear-frequency artefact**l=2 Multiplet Frequency Asymmetries**No magnetic field Now apply B field... Power m =0 Frequency m =+2 m =-2**l=2 Multiplet Frequency Asymmetries**Pattern becomes asymmetric Power m =0 Frequency m =+2 m =-2**l=2 Multiplet Frequency Asymmetries**Pattern asymmetry given by: Power an m =0 Frequency m =+2 m =-2**l=2 Multiplet Frequency Asymmetries**GOLF BiSON Chaplin et al., MNRAS, in press**l=2 Multiplet Frequency Asymmetries**Chaplin et al., MNRAS, in press**l=2 Multiplet Frequency Asymmetries**BiSON: asymmetric minus symmetric multiplet model frequency 864-d data set**Low-l Peak Asymmetries**BiSON: asymmetric- minus symmetric-peak model frequency 864-d data set**Rotational Splittings (Synodic)**Chaplin et al., 2001, MNRAS, 327, 1127**Impact of Fitting Model**Different assumed component height ratios cf. Chaplin et al., 2001, MNRAS, 327, 1127**Sidereal Splittings from 3456-d spectrum**Median 431.8 2.7 nHz Unweighted 430.5 2.8 nHz Weighted 430.1 1.2 nHz