The Solar Oblateness Measured On Board The PICARD Spacecraft, and The Solar Disk Sextant Instrument Gérard Thuillier1, Alain1 Hauchecorne1, Sabatino Sofia2, Terry Girard2, Jean-François Hochedez1, Abdenour Irbah1, Jean-Pierre Marcovici1, Mireille Meissonnier1, Mustapha Meftah1, Ulysses Sofia1, and the PICARD team 1 LATMOS-CNRS (F), 2 Yale University (US), 3 American University (US) . OUTLINE (1) Title (2) PICARD Mission (3) and (4) SODISM instrument (5) Why and how to measure the solar oblateness? (6) Method (7) Results (8) SDS instrument (9) SDS results (10) The Yale Convective Zone model (11) Comparison and discussion (12) Conclusion

THE PICARD mission LATMOS (F) Yale University IRMB (B) GSFC PMOD (Ch) OCA Meudon Obs. Nice University IAS LMD DAPNIA-CEA Yale University GSFC JPL NRL CSA / EC ILWS PICARD was launched on 15 June 2010 in a sun synchronous orbit. It consists of a microsatellite carrying four instruments: two radiometers (PREMOS and SOVAP), a bolometric sensor and an imaging telescope (SODISM). Two other presentations will be given on PICARD: to complete with the reference

SODISM INSTRUMENT (2) SODISM instrument is an imaging telescope observing in four wavelength domains equipped with a 2 K x 2 K CCD detector. The payload is actively pointed on the Sun with 0.2 arcsecond accuracy The wavelenghts are chosen in the solar photospheric continuum and in the Ca II line at 393 nm to monitor the occurrence of active regions.

SODISM OPTICAL SCHEMATICS Sun Image generated by the telescope Image on the CCD Image after the annular mirror primary mirror Image at the guiding focus 4 guiding detectors Interference filters 4 prisms Entrance window SODISM OPTICAL SCHEMATICS

Why and how to measure the solar oblateness? Why: The solar oblateness is the result of the internal rotation of the Sun. As a consequence, it can test the rotation properties determined from helioseismology. In addition, it determines the quadrupole moment of the Sun, responsible for producing the advance of Mercury’s perihelion. Since this phenomenon is due to general relativistic effects, the measurement is also important for basic physics. How: The oblateness measurements are obtained during special operations in which the spacecraft turns around the Sun direction. The rotation, made by 30° angular increments, allows us to determine the instrument optical distortion and the solar oblateness.

PICARD/SODISM

SODISM Oblateness Determination

SODISM Oblateness Results (preliminary) 90° 135° 45° MDO 535 DL: 2011-07-04 Ang Oblateness 0 4.7 ± 1.2 x10-6 45 2.6 ± 1.2 90 2.2 ± 1.1 135 6.7 ± 1.2 MDO 535 RS: 2011-07-15 0 6.9 ± 1.9 x10-6 45 2.7 ± 1.7 90 -0.2 ± 1.4 135 5.0 ± 1.6 MDO 782 DL: 2011-05-14 0 5.3 ± 1.2 x10-6 45 7.3 ± 1.0 90 3.9 ± 1.0 135 6.8 ± 0.9 0°

Solar Disk Sextant (SDS)

SDS Oblateness Determination

THE YALE MODEL OF THE SOLAR INTERIOR TWO-DIMENSIONAL STRUCTURE AND EVOLUTION EMPHASIS ON CONVECTION ZONE INCLUDES MAGNETIC FIELDS, DIFFUSION, ROTATION, AND TURBULENCE HIGH PRECISION TO BE ABLE TO HANDLE WITH SMALL CHANGE MOST ACCURATE MICRO-PHYSICS CURRENTLY AVAILABLE OBJECTIVES TO DETERMINE THE PHYSICAL MECHANISM FOR SOLAR VARIABILITY WITH CLIMATE CONSEQUENCES, BY MEASURING W=dlnR/dlnL, and DETERMINING THE INTERNAL SOLAR CONFIGURATIONS THAT LEAD TO IT. USE W AND OLD VALUES OF R (MEASURED e.g. FROM SOLAR ECLIPSES, TO DETERMINE PAST VALUES OF THE SOLAR LUMINOSITY.

COMPARISON AND DISCUSSION

CONCLUSION References:

Not fpr use in the presentation (part of the submitted abstract) SODISM, an imaging telescope with a 2K x 2K CCD detector, is dedicated to the measurement of the solar diameter and the limb shape. Although the data processing is still in a validation phase, we already present some preliminary results concerning the solar oblateness. These measurements are obtained during a special operation in which the spacecraft turns around the Sun direction. The rotation, made by 300 angular increments, allows us to determine the instrument optical distortion and the solar oblateness. The method used to extract this information will be described. We shall present the preliminary results as a function of wavelength, and compare them with measurements obtained with the SDS instrument, and with the predictions from theoretical modeling