Ilya Ilyin

Submitted: 23 February 2026 You are already at the latest version Background: The presence of alkali species in ground-based spectra of comets is complex. The observed abundance ratios deviate from solar composition, suggesting alkali ejection from phenoxides reacting with carbon dioxide at the nucleus surface.

First-light spectra of the Sun as a star taken by SDI-POL, the Solar Disk Integration POLarimeter feeding the PEPSI night-time spectrograph at the LBT. The top panel shows the full wavelength range (383 - 907 nm) covered by SDI-POL. The color of the Stokes I spectra indicates the individual cross dispersers; dark blue (=CD 1) to dark red (=CD 6). The line at the bottom represents the normalized Stokes V Q & U signal on the same intensity scale as Stokes I.

1 SCIENTIFIC MOTIVATION High-precision polarimetry becomes more and more center stage for modern astrophysics. Having been the essential tool for many decades to determine, for example, surface and atmospheric properties of our solar system planets prior to space exploration (e.g., Geake & Dollfus 1986), or determining the many facets of solar and stellar magnetic activity (e.g., Reiners 2012), it is now becoming again a desired tool for exoplanet research (e.g., Kostogryz et al.