Hubble Space Telescope's Unique Role in Studying Evolved Stars and Stellar Mass Loss
A team of thirteen astrophysicists has submitted a white paper to the Space Telescope Science Institute arguing that the Hubble Space Telescope's high-resolution ultraviolet spectroscopic instruments remain irreplaceable for studying the atmospheres and mass-loss processes of evolved stars. The paper, submitted in response to STScI's Hubble 2030s community call, highlights that HST/STIS operates in a unique observational parameter space — near- and far-ultraviolet spectroscopy at resolutions of R~30,000–100,000 — that no current or near-term facility can replicate. This matters because evolved stars are major drivers of chemical enrichment and dust production in galaxies, yet the physical mechanisms initiating their mass loss remain poorly understood.
The white paper, authored by Saberi et al. and posted to arXiv in May 2026, makes the case that evolved giant stars — which return large fractions of their mass to the interstellar medium through stellar winds — cannot be adequately studied without continued access to Hubble's Space Telescope Imaging Spectrograph (STIS) in the ultraviolet. The authors note that the atmospheric structure, chromospheric heating, and onset of mass loss in these stars are poorly constrained observationally, partly because the relevant physical processes — including pulsation, shocks, convection, and possible magnetic activity — are not fully understood even in the Sun. High-resolution NUV and FUV spectroscopy is identified as the critical diagnostic tool for determining the thermal, density, and velocity structure of these extended stellar atmospheres. The paper argues that such observations would provide essential benchmarks for stellar atmosphere models and would complement data from ALMA and ground-based optical observatories. The authors also frame continued HST UV capabilities as foundational for defining the scientific requirements of the proposed Habitable Worlds Observatory (HWO). The white paper was submitted directly to STScI's Hubble 2030s community planning process, signaling an effort by the stellar astrophysics community to influence prioritization of HST observing programs in the coming decade.
What's missing
The white paper does not specify the current operational status or projected lifetime of HST/STIS, nor does it quantify how many evolved stars have already been observed at the required UV resolution, making it difficult to assess how much of the scientific program remains to be completed.
What different sources said
- arXiv astro-phCenter
The unique capabilities of HST for stellar physics: Probing Atmospheric Structure, Chromospheres, and Mass Loss of Evolved Stars
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