We propose to perform SOT observations, using SP and simultaneous BFI in the G-band. The first results we obtained with SOT/SP show a dependence of the line formation depths with respect to the latitude and to the presence of magnetic fields. We now wish to investigate further these effects. In order to get continuous coverage in latitudes, the slit has to be oriented along the North-South axis and successively positioned in thirteen different positions which are given in Fig. 1. Furthermore, we need to have the solar equator at the center of the disk image, meaning that we wish to observe at a date when the inclinaison angle of the solar polar axis, B0, is near zero (polar axis in the plane of the sky). Therefore the right period for our observations would be the first two weeks of December when B0 is below 1in absolute value.
We also wish to perform measurements with the slit orientated radially along the@solar equator, at seven positions in the west-east direction (see Fig. 1). As we are at the beginning of the rising solar magnetic cycle we do not except to see active regions along the equator. The measurements along the equator will give access to the line formation depth variations over network and intranetwork regions at latitude zero, which cannot be measured in any other radial direction (the perpective effect vanishes when the heliocentric angle is zero).
We will use SP in the Normal map single side mode and simultaneously BFI in the G-band in order to get 2D images of the context at each slit position.
₯ Normal scans: Scan of 13 regions of 164 arcsec x 4.8 arcsec each, along the North-South polar axis.
For each region, a scan should take about 2.5 minutes. The same observation is run 16 times, which amounts to a total of 40 minutes for a given region. The center of the slit for the 13 scans is positioned from center to limb on the North-South axis at the Center, North 152 ", 304", 456", 608", 760" and 912" (with a small overlap of 12" between two successive positions) and at symetrical positions in the southern hemisphere. as shown in Fig. 1. The objective is to achieve a good polarimetric accuracy for studies of the magnetic field effects. Estimated total time for 13 positions: 520 minutes
₯ Normal scans: Scan of 7 regions of 164 arcsec x 4.8 arcsec each, along the East-West equator The 7 scans are positioned at disk center, }304", }608" and }912" along the equator and the slit is orientated along the equator. For each region, a scan should take about 2.5 minutes. The same observation is run 16 times, which amounts to a total of 40 minutes for a given region. Estimated total time for 7 positions: 280 minutes
₯ BFI in G-band at each slit position with 211"x 111" FOV and a cadence of 5 minutes (one image every two scans)
The overall requested observing time is 800 minutes. The data volume is 20x16x[30x(1024x112x1x4)]= 9 GBits for the SP data and 20x8x[2048x1024]= 670 MBits for the BFI data.