A pre-existing spectropolarimeter is described from the user's
point of view, and the important factors affecting its operation as
a high precision device are fully explained. The instrument is
applied to studies of the atmospheres of Jupiter and Saturn, and of
properties of grains in the interstellar medium.
Linear and circular polarisation measurements have been made
of the integrated discs of both Jupiter and Saturn at moderate
resolution (50 Ą̊). Enhancements in the linear polarisation across
the 7270 Ą̊ methane band are found in both planets. The effect is
attributed to the increased importance of low order scattering in
the centre of the band since here higher levels of the atmosphere
are being probed than in the continuum. It is suggested that
circular polarisation variations across this band seen in Jupiter
are caused by total internal reflection in ammonia aerosols.
Polarisation measurements have also been made across other bands in
the spectra of each planet. Continuum circular polarisation measurements have been obtained of Saturn at phase angle 2°.7. A large
enhancement in the circular polarisation is observed, increasing
very rapidly towards longer wavelengths, reaching 0.15% by 7400 Ą̊.
A future program of research is detailed.
Linear polarisation measurements in the range 3100 Ą̊ to 7600 Ą̊
have been obtained on three stars whose light has been attenuated
and polarised by the interstellar medium. The stars are 5 Ophiuchi,
55 Cygni and X Aurigae. Structure in the polarisation of 5 Ophiuchi
has been detected with scale lengths of 400 Ą̊ to 1400 Ą̊ at wavelengths
around 6000 Ą̊. No exact correspondence is found with published high
quality extinction curves of various stars. The structure is tentatively
suggested as being due to magnetite impurities in large grains. A
broad (100 Ą̊ to 200 Ą̊) feature has also been found in the polarisation
of this star centred on 4100 Ą̊. This appears to arise in larger than
average grains and may be associated with an extinction feature seen
at slightly longer wavelengths in other stars. It may be due to an
absorption in the grain mantles. Broad band variations in the position
angle of polarisation observed in all three stars have been interpreted
as implying multiple dust clouds in the lines of sight to each of
these stars. A future program of research is mapped out.