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3. The GOLF sensitivity to velocity measurements

When a celestial rotating body is observed with a high spectroscopic resolution instrument (like GOLF), were this resolution is smaller than the solar linewidth, it is possible to find sensitivity differences over the whole disk (Brookes et al. 1978b). In fact, this can be calculated by instantaneously taking the images of tex2html_wrap_inline1333 and tex2html_wrap_inline1335 by appropriate integration of Eq. (1 (click here)) at any epoch of the year. Figure 3 (click here), shows the result obtained for the sensitivity variation across the solar disk. In the nearest symetrical case, around end September where V is only tex2html_wrap_inline1117 100 ms-1, there is a factor of 4.05 for the red component and 3.85 for the blue one between the maximum and the minimum contributions in the solar disk. In the less symetrical case, around April where tex2html_wrap_inline1343 ms-1, the factors are 3.96 and 3.73.

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Figure 3:   Maps of the relative contributions of each point over the solar disk to the scattered intensities at each wing of the sodium doublet, tex2html_wrap_inline1335 and tex2html_wrap_inline1333 (left and right respectively) as they are measured by the GOLF instrument. We have considered only the Zeeman components without the magnetic modulation

Comparing the sensitivity differences between the two wings we find that it is less than a tex2html_wrap_inline1351 and during the year it changes tex2html_wrap_inline1353. Moreover, in April, the reduction of the sensitivity due to the change of the working points is less than a tex2html_wrap_inline1355. In conclusion, the selected working points show small differences in their sensibility during the year and between the two wings.

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