1. The SDS, and Variations of the Solar Diameter: Flight 11 (October 16, 2009) Sabatino Sofia Yale University New Haven, CT, USA

2. The SDS is a balloon-borne metrologic instrument that measures the SOLAR DIAMETER AND ASPHERICITY It has flown in Fall 1992, 1994, 1995, 1996, and 2009 from Fort Sumner, NM Future flights, especially connected with PICARD, are being considered.

3. RESEARCH TEAM American University (U.J. Sofia) CNRS/S.d’A (G. Thuillier, D. Djafer) CSA (Stella Melo) NASA/GSFC (W. Heaps, L. Twigg, E. Georgieva) Yale University (S. Sofia)

4. SDS Principle

10. S = (D – d)/F = W (1 – d/D)

11. Differences between existing diameter measurements Ground-based vs. space based Wavelength of observation Analysis Method Calibration These issues are extensively described in a paper by Djafer, Thuillier and Sofia, ApJ, 676, 651, 2008.

12. Ground-based measurements are affected by terrestrial atmosphere Seeing is 1”-4”, and we need sensitivity of mas. This cannot be simply solved by statistics, since atmospheric turbulence is not random.

13. Once you go to space, there are 2 measurements: SoHO/MDI SDS SoHO/MDI is not a metrologic instrument. It has not been calibrated before launch, and cannot be calibrated in space. The only metrologic instrument to measure the solar diameter is the SDS.

16. The MDI results claim an accuracy of a few mas. over more than a decade This is equivalent to knowing the effective focal length to an accuracy of a few microns over this time period. The instrument is frequently refocused. Large corrections are made through “characterization” i.e. on the basis of a “thermal model” not calibrated before flight. There are corrections for aging Etc.

17. The previous corrections are made in addition to distance corrections that are well understood. By contrast, the SDS can separate instrumental changes (regardless of its origin) from changes of the solar diameter. PICARD can calibrate scale in two separate ways: Stellar pairs Wedges (similar to SDS)

18. Philosophical difference: SDS-PICARD: We determine the scale (arc sec/mm) and its changes regardless of the cause. MDI, RHESSI *, etc: They correct for each known instrumental process, and assume the rest is solar change. * RHESSI only claims accuracy for the asphericity determination.

19. Determining the solar diameter is a complex process When we look at the image of the Sun obtained in any detector, we do not see the Sun, but an image obtained through a typically complex optical system. Besides the peculiar solar issues described earlier, we also have general optical distortion effects that we have long ago learned from stellar astrometry

20. ORIGIN OF PRINCIPAL OPTICAL DISTORTION TILT OF THE DETECTOR PLANE COLOR CHARGE TRANSFER EFFECT CLASSICAL DISTORTION COMA POSSIBLE CROSS TERMS

21. subtract background level read data (HK+CCD) apply photometric coefs preliminary edge detection subtract ghost images get next cycle filename final edge detection transform to focal-plane x,y correct for distortion fit direct & reflected circles find minimum gap output gap, sep, R d, R r, etc. odd/even offset & spike filter flight-cycle filename list output relevant HK “New” Yale SDS Flight Data Reduction Pipeline distortion coefs photom. coefs PDS xy's of CCDs

22. normalize to 1 AU cull/average by rotation angle correct for refraction cycle#, gap, sep, R d, R r, etc. output diameter & oblateness “New” Yale SDS Flight Data Reduction Pipeline (cont.) cycle#, HK (time, rotat., etc) Output from program #1 becomes input for program #2:

23. When you need sensitivity of 1 part in 10 6, and very complex analysis procedures, you run the risk that the results reflect the method rather than the object measured. The incompatible results claimed by different authors regarding the solar diameter confirm this. WE NEED TO PROCESS THE DATA TO THE POINT OF PRODUCING THE DIAMETER, AND THEN PUBLISH IT AS SOON AS POSSIBLE FOR THE BROAD SCIENTIFIC COMMUNITY TO EXPLORE ITS IMPLICATIONS

26. SDS/PICARD SYNERGY PICARD measurements are complex, and their analysis is very demanding. Analyzing the SDS data obtained before the PICARD launch has assisted development and testing of the PICARD algorithms. This has accelerated PICARD science productivity. The 2009 SDS flight, added to the earlier and the proposed follow up flights during and after PICARD will enhance the science value of the mission by: Providing validation of measurements Allowing normalization of past results Allowing the extension of the PICARD mission beyond its lifetime.