  The advent of Gaia, capable of measuring stellar wobbles caused by orbiting
planets, raised an interest to the astrometric detection of exoplanets. Another
source of such wobbles (often also called jitter) is stellar magnetic activity.
A quantitative assessment of the stellar astrometric jitter is important for a
more reliable astrometric detection and characterisation of exoplanets. We
calculate the displacement of the solar photocentre due to the magnetic
activity for an almost 16-year period (February 2, 1999 - August 1, 2014). We
also investigate how the displacement depends on the spectral passband chosen
for observations, including the wavelength range to be covered by the upcoming
Small-JASMINE mission of JAXA. This is done by extending the SATIRE-S model for
solar irradiance variability to calculating the displacement of the solar
photocentre caused by the magnetic features on the surface of the Sun. We found
that the peak to peak amplitude of the solar photocentre displacement would
reach 0.5 mas if the Sun were located 10 pc away from the observer and observed
in the Gaia G filter. This is by far too small to be detected by the Gaia
mission. However, the Sun is a relatively inactive star so that one can expect
significantly larger signals for younger, and, consequently, more active stars.
The model developed in this study can be combined with the simulations of
emergence and surface transport of magnetic flux which have recently became
available to model the astrometric jitter over the broad range of magnetic
activities.
