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Astron. Astrophys. 346, 626-632 (1999)

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5. GOLF theoretical sensitivity to magnetic measurements

Using the same numerical model that has produced the artificial data set, we can calculate the sensitivity of GOLF to the magnetic field measurements, or, in other words, how the magnetic field of the Sun appears when it is seen through the GOLF experiment (before making the integration). To reduce the errors from the interpolation procedure, we have computed the eight intensities of GOLF at a given time and then, we have applied Eq. (18) to obtain the magnetic field for each point over the solar surface. The result gives an almost flat image with an average integrated value of [FORMULA] G corresponding to a [FORMULA] [FORMULA] G. However, looking in detail at a level of [FORMULA] G we see sensitivity variations across the solar surface. In Fig. 2 a contour plot of the Sun has been drawn showing that in the western hemisphere the sensitivity is higher and concentrated in a circle around half of the solar projected radius. This effect is correlated with the velocity sensitivity (See García et al. 1998) and is due to the coupling between the limb darkening function, the solar differential rotation and the red shift velocity. The sensitivity differences over the solar surface are [FORMULA] mG and vary during the year as a consequence of the spacecraft line-of-sight velocity.

[FIGURE] Fig. 2. Sensitivity differences on the solar surface seen by the GOLF instrument.

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© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999