Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph. (arXiv:1812.03990v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Shestov_S/0/1/0/all/0/1">S. V. Shestov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhukov_A/0/1/0/all/0/1">A. N. Zhukov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Seaton_D/0/1/0/all/0/1">D. B. Seaton</a>
Context: ASPIICS is a novel externally occulted solar coronagraph, which will
be launched onboard the PROBA-3 mission of the European Space Agency. The
external occulter will be placed on the first satellite approximately 150 m
ahead of the second satellite that will carry an optical instrument. During 6
hours per orbit, the satellites will fly in a precise formation, constituting a
giant externally occulted coronagraph. Large distance between the external
occulter and the primary objective will allow observations of the white-light
solar corona starting from extremely low heights 1.1RSun. Aims: To analyze
influence of optical ghost images formed inside the telescope and develop an
algorithm for their removal. Methods: We implement the optical layout of
ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential
regimes. We identify sources of the ghost contributions and analyze their
geometrical behaviour. Finally we develop a mathematical model and software to
calculate ghost images for any given input image. Results: We show that ghost
light can be important in the outer part of the field of view, where the
coronal signal is weak, since the energy of bright inner corona is
redistributed to the outer corona. However the model allows to remove the ghost
contribution. Due to a large distance between the external occulter and the
primary objective, the primary objective does not produce a significant ghost.
The use of the Lyot spot in ASPIICS is not necessary.
Context: ASPIICS is a novel externally occulted solar coronagraph, which will
be launched onboard the PROBA-3 mission of the European Space Agency. The
external occulter will be placed on the first satellite approximately 150 m
ahead of the second satellite that will carry an optical instrument. During 6
hours per orbit, the satellites will fly in a precise formation, constituting a
giant externally occulted coronagraph. Large distance between the external
occulter and the primary objective will allow observations of the white-light
solar corona starting from extremely low heights 1.1RSun. Aims: To analyze
influence of optical ghost images formed inside the telescope and develop an
algorithm for their removal. Methods: We implement the optical layout of
ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential
regimes. We identify sources of the ghost contributions and analyze their
geometrical behaviour. Finally we develop a mathematical model and software to
calculate ghost images for any given input image. Results: We show that ghost
light can be important in the outer part of the field of view, where the
coronal signal is weak, since the energy of bright inner corona is
redistributed to the outer corona. However the model allows to remove the ghost
contribution. Due to a large distance between the external occulter and the
primary objective, the primary objective does not produce a significant ghost.
The use of the Lyot spot in ASPIICS is not necessary.
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