Slowly Rotating M Dwarfs with Unusually Strong Magnetic Fields: Interpreting the Data in Terms of How Stars Acquire Fields and How They Lose Fields
- 1University of Delaware
Abstract
L. T. Lehmann et al. (2024, hereafter L24) have reported on the presence of “unusually strong” (20-200 G) large-scale magnetic fields in six M dwarfs: four of the stars are probably completely convective, while two of the stars are probably only partially convective. A striking feature of all six stars is that they are all unusually slow rotators, with rotational periods of 40–190 days. Remarkably, L24 report that the field strengths on these six slow rotators are “similar to those of M dwarfs rotating significantly faster.” One further M dwarf (YZ Ceti) which combines slow rotation with an even stronger field (276 G) has recently been reported by A. Biswas et al. To account for these strongly magnetic but slowly rotating stars, L24 have suggested that dynamos in the slow rotators (by means of which the stars acquire magnetic fields) must be operating in a different regime from that which operates in faster rotators. Here, I suggest an alternate hypothesis based on two apparently independent results in the literature: (1) the presence of “rugged invariants” in magnetohydrodynamic turbulence, and (2) the paucity of empirical evidence for coronal mass ejections from flare stars. In the case of the six “unusually strong-field” stars in the L24 sample, I hypothesize that, as well as considering how stars acquire magnetic fields, it is also important to consider the processes by which those stars lose magnetic fields.
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BibTeX
@article{mullan2026slowly,
title = {{Slowly Rotating M Dwarfs with Unusually Strong Magnetic Fields: Interpreting the Data in Terms of How Stars Acquire Fields and How They Lose Fields}},
author = {D. J. Mullan},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea4a1},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea4a1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Slowly Rotating M Dwarfs with Unusually Strong Magnetic Fields: Interpreting the Data in Terms of How Stars Acquire Fields and How They Lose Fields
AU - D. J. Mullan
PY - 2026
DA - 2026/10/12
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea4a1
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea4a1
AB - L. T. Lehmann et al. (2024, hereafter L24) have reported on the presence of “unusually strong” (20-200 G) large-scale magnetic fields in six M dwarfs: four of the stars are probably completely convective, while two of the stars are probably only partially convective. A striking feature of all six stars is that they are all unusually slow rotators, with rotational periods of 40–190 days. Remarkably, L24 report that the field strengths on these six slow rotators are “similar to those of M dwarfs rotating significantly faster.” One further M dwarf (YZ Ceti) which combines slow rotation with an even stronger field (276 G) has recently been reported by A. Biswas et al. To account for these strongly magnetic but slowly rotating stars, L24 have suggested that dynamos in the slow rotators (by means of which the stars acquire magnetic fields) must be operating in a different regime from that which operates in faster rotators. Here, I suggest an alternate hypothesis based on two apparently independent results in the literature: (1) the presence of “rugged invariants” in magnetohydrodynamic turbulence, and (2) the paucity of empirical evidence for coronal mass ejections from flare stars. In the case of the six “unusually strong-field” stars in the L24 sample, I hypothesize that, as well as considering how stars acquire magnetic fields, it is also important to consider the processes by which those stars lose magnetic fields.
SN - 0004-637X
SN - 1538-4357
ER -