  Context: In studies of the solar spectrum relative to spectra of solar twin
stars, it has been found that the chemical composition of the Sun seems to
depart systematically from those of the twins. One possible explanation is that
the effect is due to the special aspect angle of the Sun when observed from
Earth, as compared with the aspect angles of the twins. Thus, a latitude
dependence of the solar spectrum, even with the heliocentric angle constant,
could lead to effects of the type observed.
  Aim: We explore a possible variation in the strength of certain spectral
lines, used in the comparisons between the composition of the Sun and the
twins, at loci on the solar disk with different latitudes but at constant
heliocentric angle.
  Methods: We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope
on La Palma to record spectra in five spectral regions in order to compare
different locations on the solar disk at a heliocentric angle of 45 deg.
Equivalent widths and other parameters are measured for fifteen different lines
representing nine atomic species.
  Results: The relative variations in equivalent widths at the equator and at
solar latitude 45 deg are found to be less than 1.5 % for all spectral lines
studied. Translated to elemental abundances as they would be measured from a
terrestrial and a hypothetical pole-on observer, the difference is estimated to
be within 0.005 dex in all cases.
  Conclusion: It is very unlikely that latitude effects could cause the
reported abundance difference between the Sun and the solar twins. The accuracy
obtainable in measurements of small differences in spectral line strengths
between different solar disk positions is very high.
