The Sunrise Chromospheric Infrared Spectro-Polarimeter SCIP: An Instrument for SUNRISE III

Abstract The Sunrise balloon-borne solar observatory is equipped with a one-meter aperture optical telescope, offering a unique platform for uninterrupted seeing-free observations across ultraviolet, visible, and infrared wavelengths from altitudes higher than 33 km. For the third flight of the upgraded Sunrise observatory conducted in 2024, now called Sunrise iii , a new spectro-polarimeter called the Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) was developed for observing near-infrared wavelength ranges around 770 nm and 850 nm. These wavelength ranges contain many spectral lines, including two of the Ca ii infrared triplet, K i D1 and D2 lines, and multiple Fe i lines, that are sensitive to solar magnetic fields and velocities in the photosphere and chromosphere. SCIP consists of a grating spectrograph in which polarimetric measurements are conducted using a rotating waveplate as a modulator and polarizing beam splitters placed in front of the cameras. The spatial and spectral resolutions are $0.21''$ 0.21 ″ and $1\times10^{5}$ 1 × 10 5 , respectively, and a polarimetric sensitivity of 0.03% (1 $\sigma$ σ ) of the continuum intensity is achieved with a 10 s integration time per a resolution element. To achieve high-precision detection of small polarization signals, we carefully designed the optical and mechanical systems, polarization components, control electronics, and onboard data processing. Together with the other post-focus instrumentation developed for Sunrise iii , the Sunrise Ultraviolet Spectropolarimeter and Imager (SUSI) and the Tunable Magnetograph (TuMag) visible imaging spectro-polarimeter, SCIP provides novel observations that help elucidate energy transfer and time-dependent phenomena across the solar photosphere and chromosphere.