Expanding stellar horizons with polarized light

TL;DR

This paper highlights the potential of polarized light measurements in astronomy, especially for stars, to unlock new insights into stellar magnetic fields, evolution, and internal structures, which are currently under-explored due to instrumentation limitations.

Contribution

It advocates for dedicated spectro-polarimetric instruments to study stellar magnetic fields across various types and stages, linking surface magnetism to internal processes and advancing asteroseismology.

Findings

Polarimetry can reveal weak and strong stellar magnetic fields.

Combining spectro-polarimetry with asteroseismology enhances stellar modeling.

Time-resolved spectro-polarimetric data can improve understanding of stellar evolution.

Abstract

The polarization of light is a critically under-utilized, rich source of information in astronomy. For stars in particular, surface magnetism polarization that can be detected and measured with spectro-polarimetry. Many questions about these surface fields remain unanswered due to a lack of dedicated instruments capable of probing weak and strong surface magnetic fields for the entire mass range of stars, from M-dwarfs (and even substellar objects) to massive O-type stars at different evolutionary stages and metallicities. These questions range from the origin of these fields to their true incidence rate throughout the stellar population and the dependence on metallicity. Magnetic fields, although currently often excluded from stellar evolution models, play an important role in stellar evolution. Connecting the surface fields to internal fields through asteroseismology will instigate a new era of understanding stellar evolution and the transport of angular momentum and chemical elements throughout stellar interiors, also impacting our understanding of star-planet interactions and stellar remnants. Polarimetry is also an under-utilized tool to observationally constrain the mode identification of nonradial oscillations, which lies at the basis of accurate asteroseismic parameter estimation at percentage-level for stellar radii, masses, ages, internal rotation, and magnetic field strengths. Combining strong constraints on mode identification and surface magnetic properties through the acquisition of time-resolved, high-resolution and high-signal-to-noise (S/N) spectro-polarimetry and spectroscopy promises to bring leaps forward in our understanding of stellar structure, particularly when combined with long-term space photometric data from past, current, and future missions.