Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2601.05313

Overestimated Pressure Broadening Misleads Model Spectra in Cool M Dwarf Stars

Ana Glidden·Veronika Witzke·Alexander I. Shapiro·Sara Seager
View original source ↗Read source document ↗Export metadata ↓

Abstract

Available one-dimensional stellar models fail to reproduce the observed spectrum of the ultracool M dwarf TRAPPIST-1. In particular, current models predict strong iron hydride (FeH) absorption due to the Wing-Ford bands at 0.99$μ$m, yet this spectral feature is only weakly present in TRAPPIST-1 and other mid-to-late M dwarf stars. Additionally, the shape of the continuum between the water bands in the near-infrared does not match between models and observations. Here, we show that assumptions about pressure broadening, specifically van der Waals broadening, have a dramatic effect on modeled broadband spectral features. We use Merged Parallelized Simplified-ATLAS to generate synthetic spectra over a range of van der Waals broadening strengths, adopting 1D PHOENIX temperature-pressure structures. We find that minimal broadening best matches the observed FeH profile at 0.99$μ$m and in the pseudocontinuum between the large water bands. These results suggest that broadening prescriptions derived for Sun-like stars are not valid for lower-mass stars and that pressure broadening for molecular lines in cool stellar atmospheres must be reevaluated. Refining pressure broadening treatments will improve the accuracy of M dwarf spectral models, enabling more reliable determinations of stellar properties and atmospheric compositions of planets orbiting M dwarfs.

Explore related subjects

astro-ph.SRastro-ph.EP

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Ana Glidden, Veronika Witzke, Alexander I. Shapiro, Sara Seager. 2026-01-08. Overestimated Pressure Broadening Misleads Model Spectra in Cool M Dwarf Stars. https://arxiv.org/abs/2601.05313

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Image Profile (IMPRO) Fitting of Massive Protostars. I. Method Development and Test Cases of Cepheus A and G35.20-0.74N

Massive stars play a critical role in the evolution of galaxies, but their formation remains poorly understood. One challenge is accurate measurement of the physical properties of massive protostars, such as current stellar mass, envelope mass, outflow cavity properties, and system orientation. Spectral energy distribution (SED) fitting is widely-used to test models against observations. The far-infrared SED traces cold dust in envelopes, while the near- and mid-infrared (MIR) probes emission from outflow cavities and/or the inner envelope. However, SED fitting has degeneracy limiting its ability to yield accurate measurements of protostellar properties. Here, we develop image profile (IMPRO) fitting as a method to improve the characterization of protostars. We utilize brightness distributions from multi-wavelength MIR images of massive protostars taken by SOFIA/FORCAST as part of the SOFIA Massive Star Formation (SOMA) survey to constrain protostellar properties via comparison to a grid of radiative transfer models. We develop a fitting pipeline to extract information along the outflow axis, which is then combined with the SED fitting to yield improved constraints on protostellar properties. We apply the IMPRO fitting method on the nearby massive protostar Cepheus A, finding that its properties become more tightly constrained compared to SED fitting, especially in the inclination of the source. However, for the more distant G35.20-0.74N, we find that the spatial resolution of SOFIA/FORCAST limits the utility of this combined fitting pipeline. However, higher resolution MIR observations, e.g., with JWST, are expected to greatly expand the applicability of this fitting technique to protostars across the Galaxy.

astro-ph.SR↗
arXiv2026

High-Resolution Modelling of Coronae and Winds in Solar-type Stars with Varying Rotation Rates I. X-ray Coronae

Stellar coronae are believed to be the main birthplace of various stellar magnetic activities. However, the structures and properties of stellar coronae remain poorly understood. Using the Space Weather Modelling Framework with the Alfvén Wave Solar Model (SWMF-AWSoM) and dynamo-generated surface magnetic maps, here we model the coronae of four solar-type stars. By incorporating the Sun, our work covers a range of stars with the rotation varying from 1.0 to 23.3 $Ω_\odot$ (periods of 25 to 1 days). Guided by observations, we scale the magnetic field strength with increasing rotation, covering a range between 6.0 G to 1200 G approximately. In our models, energy release associated with small-scale magnetic flux is a key source of coronal heating and is essential for reproducing realistic coronal structures. Our models capture dense (1$-$2 orders of magnitude higher than solar values) and ultra-hot ($\sim 10\,\mathrm{MK}$) coronae dominated by closed field structures. Using the CHIANTI atomic database, we also compute synthetic X-ray spectra and derive the corresponding X-ray luminosities $(L_X)$, which follow a scaling law to magnetic field $L_X \propto \langle|\mathbf{B}|\rangle^{1.75}$. Furthermore, the coronal X-ray emission is found to be rotationally modulated by the alternating presence of bright active regions and dark coronal holes. These results provide new insights into the extremely high-energy coronae of rapidly rotating solar-type stars, which differ markedly from the Sun.

astro-ph.SR↗
arXiv2026

The Common Envelope Evolution Outcome. III. the Improvement of Stellar Binding Energy with the Envelope Residual

Common-envelope evolution (CEE) is a key process in the evolution of close binary systems. Many important astrophysical objects and evolutionary stages are closely related to CEE, including white dwarf binaries, hot subdwarfs, and gravitational wave mergers. In the standard energy formalism of CEE, the binding energy of the donor envelope plays a crucial role, as it directly affects the final orbital period after CEE and serves as a key physical parameter in binary population synthesis studies. However, the currently adopted binding energy suffers from large uncertainties, mainly because the envelope binding energy of giant-branch stars varies strongly near the helium-core boundary. In addition, the expansion of the star during CEE can also affect the binding energy. To address these issues, we introduce an improved binding energy for the envelope mass residual. Based on adiabatic mass loss models, we recalculate the distribution of the CEE binding-energy parameter lambda for stars with different masses and at different evolutionary stages, and we analyse the effects of envelope mass residual and adiabatic expansion. Due to the envelope mass residual, the lambdas of some donors can increase by one to two orders of magnitude at the late red giant branch and asymptotic giant branch stages. Furthermore, we provide interpolation grids and fitting formulae for these results, which can be readily applied to various binary population synthesis codes.

astro-ph.SR↗