The Pollux European instrument concept for HWO: a high-resolution spectrograph and spectropolarimeter from the far-UV to the near-IR

TL;DR

Pollux addresses the need for simultaneous high-resolution spectroscopy and spectropolarimetry from 100 nm to 1.88 μm to study stars, exoplanets, and cosmic ecosystems. The approach uses five co-mounted high-resolution echelle spectrographs, each with a dedicated polarimeter, delivering $R ≥ 9×10^4$ in the UV and ≈$1×10^5$ in the visible/NIR, across a spectral span from $100$ nm to $1.88$ μm. A key contribution is the UV spectropolarimetry capability and the on-board Fabry-Perot comb calibration concept to avoid UV lamps, all designed for minimal cooling and high stability. The project aligns with NASA and ESA priorities for HWO by enabling exploration of magnetic fields, exoplanet atmospheres, and baryon-cycle processes across cosmic time, opening new parameter space in the UV.

Abstract

Pollux is a high-resolution spectrograph and spectropolarimeter working from 100 nm to 1.8 microns proposed for HWO by a European consortium. Pollux will allow us to study stellar and (exo)planetary systems, as well as cosmic ecosystems. For example, Pollux will provide new insights on exoplanet formation and evolution, characterization of the atmospheres and magnetospheres of stars and planets, and star-planet interactions. It will also allow us to resolve narrow UV emission and absorption lines, enabling us to follow the baryon cycle over cosmic time -- from galaxies forming stars out of interstellar gas and grains, and planets forming in circumstellar disks, to the various forms of feedback into the interstellar and intergalactic medium -- and from active galactic nuclei. The most innovative characteristic of Pollux is its unique spectropolarimetric capability in the UV, which will open a new parameter space. Its very high spectral resolution (~70000 to ~100000) and stability over a very large wavelength range will also be a major asset. In this paper, we summarize the main scientific drivers of Pollux and present its current design, technological challenges, and the Pollux consortium organization.

Figures (6)

• Figure 2: Schematic view of the current Pollux design. The caption of symbols is shown at the top center of the figure. Light flows along the black lines. The FMUV and NUV channel designs are similar, therefore only one example is shown.
• Figure 3: Optical design of an echelle spectropolarimeter on the example of FMUV channel.
• Figure 4: Spectral resolving power for reference wavelengths of the UV channels. The shaded zones correspond to the target values.
• Figure 5: Packaging and overall dimensions of the three UV sub-systems.
• Figure 6: End-to-end transmission of the FMUV channel in the MUV spectropolarimetric mode presented in the effective area units for a 6-m unobscured telescope.