1. Sushanta C. Tripathy NSO, Tucson
Comparison of Mode Parameters between Velocity and Intensity Acoustic Spectra using MDI data
Sushanta C. Tripathy
NSO, Tucson

2. CONTENTS Introduction Results using GONG pipeline: symmetric profiles
Problems in 3D asymmetric fitting
Results from 2D asymmetric fitting
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3. Introduction
Significant differences in central frequencies were found in global spectra obtained simultaneously in V and I (Harvey et al., 1998)
Difference depends on ν of the mode and can be as high as 50 μHz above cutoff frequency
Shift can not be a property of the mode and must arise from excitation mechanism
We use ring diagram techniques to investigate the properties of mode parameters from Velocity (V) and Intensity (I) filtergrams as a function of center to limb
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4. Present study We use MDI Velocity and Intensity full-disk images
Taken during 1997, April (quiet days)
Each region is a 16º square and is tracked for a period of 1664 minutes
Processed through GONG ring pipeline
Power spectra of individual days are combined to enhance the s/n ratio
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5. Power Spectrum as a function of 
V 
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6. modes are fitted using the model with symmetric profiles
for radial order n  6
200    1100 (resolution of   22)
Freq. resolution  10 Hz
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7.  - diagram from fitted spectrum
 From Velocity Power spectrum
From Intensity Power spectrum   f
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8. Center to Limb frequency differences
 Velocity
Intensity 
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9. Frequency differences as a function of radial order
 Velocity
Intensity 
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10. Differences in frequency (I – V)
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11. Differences in frequency (I – V)
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12. Differences in Frequency as a function of CL
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13. Averaged frequency differences across CL
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14. Summary so far ….
 is a function of location on the disk and increases from center to limb among velocity (and intensity)
 between V and I is a function of frequency
Difference rises rapidly at higher  (and higher )
 is a function of location and increases from disk center to limb
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15. 3D Asymmetric Fitting
We use the model with asymmetric peak profiles of Basu and Antia (1999)
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16. Results from 3D Asymmetric Fitting
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17. And fit 6 parameters, b1,b2,A0,v0,S and w0
2D Asymmetric Fitting
We take azimuthal average for each spectra to obtain 2D spectra in k-ω and fit these using asymmetric peak profiles of Antia and Basu (1999)
And fit 6 parameters, b1,b2,A0,v0,S and w0
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18. Results from 2D Asymmetric Fitting
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19. Differences in Frequency (V0 – Vp)
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20. Differences in Frequency (I0 – Ip)
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21. Differences in Frequency (Vsy – Vasy)
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22. Differences in Frequency (Isy – Iasy)
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23. Differences in Frequency (V – I)
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24. Differences in Frequency (V – I)
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25. Future Work …..
Better fitting method for 3D power spectra to obtain correct S parameter
Compare other parameters e.g. A, U, Γ
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26. THANK YOU Collaborators H. M. Antia Irene Gonzalez-Hernandez
Frank Hill Rachel Howe
Rudi Komm Cliff Toner
THANK YOU
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