Bridging magnetothermal winds and photoevaporation to model discs dispersal
Abstract
Protoplanetary disc dispersal is driven by two processes usually modelled separately: photoevaporative and magnetohydrodynamic (MHD) disc winds. Global simulations indicate that in the inner disc these are not distinct outflows but a single magnetothermal wind. We assemble a closed-form, two-phase model that respects it. A single-field-line wind, whose base is fixed by the irradiated temperature and penetration column, supplies the launch and feeds a secular evolution, with photoevaporation convolved on as a sink. The flux closure Bz∝Σq is self-limiting: for q≤1/2 depletion alone cannot demagnetise the disc, so dispersal requires independent flux loss, parameterised by the magnetic Reynolds number ℛm. Integrating the coupled system yields two regimes. Efficient flux loss (ℛm≲1) lets the magnetisation front recede by over an order of magnitude and opens a photoevaporative gap. Flux retention (ℛm≫1) drives the front outward, sustains accretion, and defers dispersal by ≈2.7~Myr. Deriving the base from stellar irradiation instead of prescribing it, we find that the cold-launch approximation is valid during the early stages of disc evolution: anchoring the base at plasma equipartition (βbase ∼ 1) confines irradiation's influence on the magnetic lever arm to the magnetothermal annulus, decoupling the peak accretion rate from the incident flux. Both regimes clear the disc inside-out, through either a photoevaporatively amplified cavity wall or an expanding magnetothermal front.
Related
- Secular evolution of viscous and self-gravitating protoplanetary discs with magnetic winds
- Secular evolution of viscous and self-gravitating protoplanetary discs with magnetic winds
- Magnetar magnetothermal evolution with Landau-quantized electrons: enhanced Joule heating due to free electron diamagnetism and the magnetar heating problem
- External photoevaporation in the center of Tr14
- Revisiting Sub-Neptune Population Synthesis: The Role of Core Luminosity in Boil-off, Photoevaporation, and the Radius Distribution
BibTeX
@misc{picogna2026bridging,
title = {{Bridging magnetothermal winds and photoevaporation to model discs dispersal}},
author = {Giovanni Picogna and Barbara Ercolano},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18334},
eprint = {2609.18334},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18334},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Bridging magnetothermal winds and photoevaporation to model discs dispersal
AU - Giovanni Picogna
AU - Barbara Ercolano
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.18334
UR - https://arxiv.org/abs/2609.18334
AB - Protoplanetary disc dispersal is driven by two processes usually modelled separately: photoevaporative and magnetohydrodynamic (MHD) disc winds. Global simulations indicate that in the inner disc these are not distinct outflows but a single magnetothermal wind. We assemble a closed-form, two-phase model that respects it. A single-field-line wind, whose base is fixed by the irradiated temperature and penetration column, supplies the launch and feeds a secular evolution, with photoevaporation convolved on as a sink. The flux closure B_z∝Σ^q is self-limiting: for q≤1/2 depletion alone cannot demagnetise the disc, so dispersal requires independent flux loss, parameterised by the magnetic Reynolds number ℛ_m. Integrating the coupled system yields two regimes. Efficient flux loss (ℛ_m≲1) lets the magnetisation front recede by over an order of magnitude and opens a photoevaporative gap. Flux retention (ℛ_m≫1) drives the front outward, sustains accretion, and defers dispersal by ≈2.7~Myr. Deriving the base from stellar irradiation instead of prescribing it, we find that the cold-launch approximation is valid during the early stages of disc evolution: anchoring the base at plasma equipartition (β_base ∼ 1) confines irradiation's influence on the magnetic lever arm to the magnetothermal annulus, decoupling the peak accretion rate from the incident flux. Both regimes clear the disc inside-out, through either a photoevaporatively amplified cavity wall or an expanding magnetothermal front.
ER -