  Twin STEREO spacecraft pre-perihelion photometric and polarimetric
observations of the sungrazing Kreutz comet C/2010 E6 (STEREO) in March 2010 at
heliocentric distances $3-28~R_{\odot}$ were investigated using a newly-created
set of analysis routines. The comet fully disintegrated during its perihelion
passage. Prior to that, a broadening and an increase of the intensity peak with
decreasing heliocentric distance was accompanied by a drop to zero polarisation
at high phase angles (~105-135{\deg}, STEREO-B) and the emergence of negative
polarisation at low phase angles (~25-35{\deg}, STEREO-A). Outside the
near-comet region, the tail exhibited a steep slope of increasing polarisation
with increasing cometocentric distance, with the slope becoming less prominent
as the comet approached the Sun. The steep slope may be attributed to
sublimation of refractory organic matrix and the processing of dust grains, or
to presence of amorphous carbon. The change in slope with proximity to the Sun
is likely caused by the gradual sublimation of all refractory material. The
polarisation signatures observed at both sets of phase angles closer to the
comet photocentre as the comet approached the Sun are best explained by
fragmentation of the nucleus, exposing fresh Mg-rich silicate particles,
followed by their gradual sublimation. The need for further studies of such
comets, both observational and theoretical, is highlighted, as well as the
benefit of the analysis routines created for this work.
