Classical Cases of Non-solar Mixing Length in Low Mass Stars
Abstract
The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter (αMLT) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable αMLT causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable αMLT to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar αMLT. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar αMLT/αMLT,⊙∼0.50−0.75 can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between αMLT and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.
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BibTeX
@misc{woody2026classical,
title = {{Classical Cases of Non-solar Mixing Length in Low Mass Stars}},
author = {Rebecca Woody and Charlie Conroy and Phillip A. Cargile and Aaron Dotter},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.13384},
eprint = {2609.13384},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.13384},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Classical Cases of Non-solar Mixing Length in Low Mass Stars
AU - Rebecca Woody
AU - Charlie Conroy
AU - Phillip A. Cargile
AU - Aaron Dotter
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2609.13384
UR - https://arxiv.org/abs/2609.13384
AB - The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter (α_MLT) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable α_MLT causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable α_MLT to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar α_MLT. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar α_MLT/α_MLT,⊙∼0.50−0.75 can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between α_MLT and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.
ER -