Transonic Solutions for Recombination-driven Stellar Winds
- 1The Hebrew University of Jerusalem
- 2California Institute of Technology
Abstract
We present an analytical stationary isentropic solution of the spherically symmetric Euler equations in the gravitational field of a star using an equation of state of ionizable monatomic gas. The solution consists of a fully ionized hydrostatic inner region, followed by a thick hydrostatic recombination region where the density decreases by orders of magnitude, the radius increases by about an order of magnitude, and the temperature decreases by a factor of 2. Within this recombination region, a large portion of the recombination energy is used for lifting the gas subsonically. This region ends at a critical point, located roughly at 10−100 au, where the gas is mostly recombined, beyond which it flows supersonically as a wind. We find the position and the quantities of the gas at the critical point and derive the mass-loss rate of the solution. We apply our solution to evolved stars, with a compact core surrounded by a high-entropy envelope. We derive the mass-loss rate as a function of time. As the star is losing mass, it goes through a sequence of our solutions, in a runaway manner which ends once most of the high-entropy envelope is lost. Recombination-driven winds are initiated once the star expands to a radius of about 1 au M / M ⊙ and are terminated on a timescale of 10 ¹ –10 ⁴ yr. We discuss the implications for common envelope evolution.
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BibTeX
@article{strusberg2026transonic,
title = {{Transonic Solutions for Recombination-driven Stellar Winds}},
author = {Ilan Strusberg and Re’em Sari and Jim Fuller},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = oct,
doi = {10.3847/2041-8213/aeb001},
url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeb001},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Transonic Solutions for Recombination-driven Stellar Winds
AU - Ilan Strusberg
AU - Re’em Sari
AU - Jim Fuller
PY - 2026
DA - 2026/10/23
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aeb001
UR - https://iopscience.iop.org/article/10.3847/2041-8213/aeb001
AB - We present an analytical stationary isentropic solution of the spherically symmetric Euler equations in the gravitational field of a star using an equation of state of ionizable monatomic gas. The solution consists of a fully ionized hydrostatic inner region, followed by a thick hydrostatic recombination region where the density decreases by orders of magnitude, the radius increases by about an order of magnitude, and the temperature decreases by a factor of 2. Within this recombination region, a large portion of the recombination energy is used for lifting the gas subsonically. This region ends at a critical point, located roughly at 10−100 au, where the gas is mostly recombined, beyond which it flows supersonically as a wind. We find the position and the quantities of the gas at the critical point and derive the mass-loss rate of the solution. We apply our solution to evolved stars, with a compact core surrounded by a high-entropy envelope. We derive the mass-loss rate as a function of time. As the star is losing mass, it goes through a sequence of our solutions, in a runaway manner which ends once most of the high-entropy envelope is lost. Recombination-driven winds are initiated once the star expands to a radius of about 1 au M / M ⊙ and are terminated on a timescale of 10 ¹ –10 ⁴ yr. We discuss the implications for common envelope evolution.
SN - 2041-8205
SN - 2041-8213
ER -