Pathways to Discovery in Astronomy and Astrophysics for the 2020s (2023) / Chapter Skim
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Appendix G: Report of the Panel on Stars, the Sun, and Stellar Populations
Appendix G: Report of the Panel on Stars, the Sun, and Stellar Populations
Pages 330-347
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From page 330... ...
The scope of the Panel on Stars, the Sun, and Stellar Populations includes stellar structure and evolution, stellar activity and variability, brown dwarfs, ground-based solar astrophysics, resolved stellar populations including star clusters, nucleosynthesis, and chemical evolution. In the course of its work, the panel reviewed and incorporated the input of over 150 white papers submitted by the astronomy and astrophysics community addressing the preceding topics, as well as broader areas of astronomy in which stars are tools for studying fundamental physics, exploring the interstellar and intergalactic media, and probing distant galaxies.
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From page 331... ...
These data are now used to study changes inside the Sun and have revealed the beginning of a new solar cycle years before its first sunspots appear on the Sun's surface. Advances in the next decade should provide more detailed understanding about how solar magnetic fields drive energetic phenomena at different spatial, temporal, and energy scales.
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From page 332... ...
have given us an empirical probe and new theoretical advancements on the equation of state of hydrogen-rich, electron-degenerate matter and the role of magnetic fields in stellar structure. Indeed, the mass-radius relationship for the lowest-mass stars cannot be explained without taking both effects into account.
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From page 333... ...
We have also learned that about 10 percent of massive stars possess strong surface magnetic fields (~0.3–20 kG) and high rotation rates (>200 km/s at the equator)
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From page 334... ...
Defining the extremities is also crucial for stellar systems because they can span a wide range in properties such as masses, rotation, magnetic fields, mass transfer rates, and so on. For star clusters and stellar populations, the range of the distribution of masses and frequency of multiple stars can be determined from observations, and these properties play a critical role in the evolution of the system.
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From page 335... ...
At the low-mass end, mass estimates to better than 10 percent are needed to understand the transition between brown dwarfs and stars. Lack of accurate masses, binarity, and rotation limits our knowledge of stars that explode as supernovae or erupt as other violent astrophysical transients.
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From page 336... ...
While proxies of chromospheric magnetic activity have been monitored for decades, measurements of magnetic fields and their configurations remain rare. These measurements are becoming more accessible through spectropolarimetry and Zeeman Doppler Imaging (ZDI)
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From page 337... ...
Among other parameters, we need to know the orbital properties and mass ratios of multiple-star systems across age, mass, mass-loss rates, and composition. While we know that multiplicity is more common in high-mass than in low-mass stars, we have incomplete information on the statistics of systems with extreme mass ratios, long orbit periods, and very low masses (e.g., brown dwarfs)
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From page 338... ...
will provide a critical reference for disentangling exoplanet and stellar signatures, essential for the robust detection of habitable Earth-like planets. In the cool atmospheres of brown dwarfs, where magnetic spot formation can be inhibited, surface asymmetries arise instead from condensate cloud structures (see Figure G.2)
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From page 339... ...
The Sun and other stars affect their environments in numerous ways, from the interaction of stellar winds, flares, coronal mass ejections (CMEs) and other forms of mass loss with surrounding disks, planetary bodies, stellar companions, and the interstellar medium, to the creation of planetary nebulae and supernova remnants and the end stages of stars.
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From page 340... ...
A massive star's evolution depends on its mass loss rate, which in turn depends on metallicity as the wind acts on the highly ionized metals produced by the star, and on magnetic field strength, now measured in 10 percent of hot stars. The winds of low-mass stars are more elusive, but the solar system provides an essential laboratory for understanding these processes.
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From page 341... ...
Athena does not have all the characteristics needed for work on stars. While Athena's microcalorimeter will provide high-resolution spectra for the most energetic phenomena such as stellar flares, studies of quiescent and/or lower energy phenomena, such as coronal heating and absorption of CMEs, would benefit from high spectral resolution at lower energies; these can be obtained with grating spectrometers.
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From page 342... ...
For high-mass stars, time and spectrally resolved X-ray line profiles will probe the clumpiness of shocks in the wind and constrain mass loss rates. Past UV spectroscopic samples are small, both in number and in wavelength coverage.
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From page 343... ...
Multi-epoch observations map stellar binaries and reveal invisible companions, probe stellar interiors through precision asteroseismic measurements, and unveil the dynamic atmospheres of cloudy brown dwarfs and massive evolving stars. Concurrent advances in spectropolarimetry are needed to map stellar magnetic field structures, particularly for the lowest- and highest-mass stars whose interior structures differ considerably from the Sun's and whose interior dynamos remain poorly understood.
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From page 344... ...
Investment is also needed to advance high-performance computing for 3D modeling of stellar interiors, atmospheres, and binary-star evolution, and to process and perform real-time analysis of the petabytes-per-day data flows anticipated in future surveys. Maximizing future science capabilities and outcomes goes beyond investment in facilities; theoretical and numerical studies are also needed to advance our understanding.
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From page 345... ...
Evolution of solar magnetic structures Broadband (<1 to >20 GHz) spatially resolved observations of the Sun and related internal changes measurements, frequency resolution better than 5 percent, time resolution of ~10 s.
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From page 346... ...
Abundance of the most metal-poor High-resolution spectrometer and spectropolarimetry stars spectropolarimeter covering wide wavelength (G-Q3) Stellar surface feature mapping domains to cover lines formed from 104 to 107 (G-Q3)
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From page 347... ...
(1) Improved atomic data for stellar spectral lines and opacities.
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