Spectroscopy and polarimetry design and flight instrument calibration for the Roman Coronagraph

Le résumé fourni par la source

The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will demonstrate spectroscopy of directly imaged exoplanets and polarization measurements of disks. The spectroscopy mode is a zero-deviation Amici prism and slit, which is deployed to the planet position after an imaging detection. The Wollaston prism polarization optics allow for imaging two orthogonal polarization states simultaneously. The CGI spectral characterization modes, designed and built at Goddard Space Flight Center (GSFC), have a spectral resolution of R≃50 in two 15% bandpasses centered at 660 and 730 nm. There are duplicate Wollaston prism channels, clocked 45 deg with respect to one another to completely characterize the instrument polarization effects and recover the Stokes parameters of the targeted disk. The Wollaston design and optical elements are a contribution by the Japanese Aerospace Exploration Agency, with final alignment and testing being done at GSFC. The spectroscopy mode is optimized to target methane absorption features, keeping the spectral resolution as low as possible to improve the signal-to-noise ratio and hence reduce detection time. We highlight the requirements for these modes, the ground-to-orbit calibration process, and the operations required to use a deployable slit on a CGI point source in the presence of a pointing error. We also provide further detail on the optomechanical design, environmental testing, optical verification process, performance of the as-built flight assemblies, and their calibration once integrated into CGI.

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