Solar oblateness as measured with the PICARD mission

PICARD is a space mission launched in June 2010. One of its scientific objectives is to study the geometry of the Sun including measurements of the solar oblateness at several wavelengths. This physical parameter is however difficult to achieve since all image defaults due to the whole system telescope-CCD affect its measurement. Rolling the satellite as already done with previous space missions allows discriminating from the telescope-CCD contribution when considering the Sun as constant during the observations. This supposes however that the telescope optical response is time-invariant during the roll operations. This is not the case for PICARD where an orbital signature is clearly observed in the solar radius obtained from its images. We have taken advantage of this effect and developed a new method to process the PICARD images to deduce the solar oblateness. This method supposes that there are both a time and an angular modulation of the solar limb due to the satellite moving on its orbit and when it is rotated around the line of sight during the specific observations. We will first give in this work an overview of the PICARD mission and present after the solar observations recorded for the oblateness measurements. The new method developed to process the data is then detailed and some results are given and discussed.