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 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. Polarimetric measurements are conducted using a rotating waveplate as a modulator and polarizing beam splitters in front of the cameras. The spatial and spectral resolutions are 0.21" and 2x10^5, respectively, and a polarimetric sensitivity of 0.03% (1sigma) of the continuum intensity is achieved within a 10 s integration time. To detect small polarization signals with good precision, we carefully designed the opto-mechanical system, polarization optics and modulation, control electronics, and onboard data processing. Together with the other post-focus instrumentation developed for Sunrise III, the Sunrise Ultraviolet Spectropolarimeter and Imager and the visible imaging spectro-polarimeter Tunable Magnetograph, SCIP provides novel and unique observations to understand the energy transfer and dynamical processes through the photosphere-chromosphere.

Figures (34)

• Figure 1: Science targets using SCIP. Spectro-polarimetric measurements of multiple spectral lines from the photosphere to the chromosphere allow us to obtain three-dimensional structures of magnetic and velocity fields and reveal the nature of the jets and MHD waves responsible for heating the atmosphere and acceleration of the solar wind. Modified from 2020SPIE11447E..0YK.
• Figure 2: Atlas spectra of the two SCIP spectral windows, (top) 850 nm and (bottom) 770 nm windows, and key spectral lines in the wavelength ranges. This solar spectral atlas shown here is compiled using data from the NSO FTS flux atlas 1984sfat.book.....K.
• Figure 3: Formation heights of key spectral lines observed with SCIP, including Ca ii 854.2 nm and 849.8 nm, K i 766.4 nm and 769.8 nm, Fe i 846.8 nm, and Si i 768.0 nm. The figure is made using a 3D MHD simulation and non-LTE radiative transfer calculation 2017MNRAS.470.1453Q. The gray scale represents temperatures within the solar atmosphere. Modified from 2020SPIE11447E..0YK.
• Figure 4: The opto-mechanical layout of the SCIP O-unit. The cover and the lighttrap structures are shown as transparent for clarity. Modified from uraguchi2023jaxarr.
• Figure 5: Block diagram of the scip electronics for observation control. The control electronics of the scip E-unit are located on the gondola E-rack. The driver electronics boxes for the pmu and smm are also located on the E-rack and controlled by the E-unit. Exposures of the three cameras are triggered by phase signals generated by the PMU, and the E-unit sends an exposure command to the cameras. The E-unit receives images taken by the three cameras and applies onboard image processing. The E-unit also sends a command to the smm to move the scan mirror. Structure and camera heaters are placed inside the O-unit to stabilize the temperature environment of the O-unit. The red boxes indicate components developed by the Japanese team, whereas the blue boxes indicate components developed by the S$^3$PC. Modified from 2020SPIE11447E..0YK.