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Composite overshoot #1003

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ac23337
[ci optional] add a step+exponential overshoot prescription
matthiasfabry May 19, 2026
2af4fa2
[ci optional] add step+exp in 20M test case
matthiasfabry May 19, 2026
1106a70
fix inconsistent Hp limiter
matthiasfabry May 19, 2026
1d4fcf8
[ci skip] fortitude fix
matthiasfabry May 20, 2026
29d10d9
[ci skip] add some doc on the philosophy of step+exp overshoot
matthiasfabry May 20, 2026
ae1e417
[ci skip] changelog entry
matthiasfabry May 21, 2026
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2 changes: 2 additions & 0 deletions docs/source/changelog.rst
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Expand Up @@ -28,6 +28,8 @@ For a more in-depth look at the new build system, see :doc:`developing/build-sys
New Features
------------

Convective overshooting now includes a ``step+exponential`` prescription.

MESA no longer stops when reactions for which special rates are set are not in the nuclear network, only a warning is printed. This is intended to make it easier to test various network sizes without having to also change the list of special reactions.

.. _Bug Fixes main:
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1 change: 1 addition & 0 deletions star/Makefile
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Expand Up @@ -111,6 +111,7 @@ SRCS := \
private/overshoot.f90 \
private/overshoot_exp.f90 \
private/overshoot_step.f90 \
private/overshoot_step_exp.f90 \
private/overshoot_utils.f90 \
private/paquette_coeffs.f90 \
private/phase_separation.f90 \
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32 changes: 24 additions & 8 deletions star/defaults/controls.defaults
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Expand Up @@ -2681,11 +2681,8 @@
! overshooting
! ____________

! There are two schemes implemented in MESA to treat overshooting:
! a step overshoot scheme and an exponential scheme.

! Parameters for exponential diffusive overshoot are described in the paper by Falk Herwig,
! "The evolution of AGB stars with convective overshoot", A&A, 360, 952-968 (2000).
! There are three schemes implemented in MESA to treat overshooting:
! a step overshoot, an exponential scheme, and the combination of both.

! Overshooting depends on the classification of the convective zone and can be different at the top and the bottom of the zone.

Expand All @@ -2699,7 +2696,7 @@

! ::

overshoot_scheme(:) = '' ! ``exponential``, ``step``, ``other``
overshoot_scheme(:) = '' ! ``exponential``, ``step``, ``step+exponential``, ``other``
overshoot_zone_type(:) = '' ! ``burn_H``, ``burn_He``, ``burn_Z``, ``nonburn``, ``any``
overshoot_zone_loc(:) = '' ! ``core``, ``shell``, ``any``
overshoot_bdy_loc(:) = '' ! ``bottom``, ``top``, ``any``
Expand All @@ -2711,11 +2708,12 @@
! ::

overshoot_f(:) = 0d0
overshoot_f2(:) = 0d0
overshoot_f0(:) = 0d0

! The switch from convective mixing to overshooting happens at a distance f0*Hp into the convection zone
! from the estimated location where ``grad_ad = grad_rad``, where Hp is the pressure scale height at that location.
! A value <= 0 for f0 is a mistake -- you are required to set f0 as well as f.
! A value <= 0 for f0 is a mistake -- you are required to set f0 as well as f (and f2 if using step+exponential).
! take a look at the following from an email concerning this:
! Overshooting works by taking the diffusion mixing coefficient at the edge
! of the convection zone and extending it beyond the zone. But -- and here's the issue --
Expand All @@ -2736,6 +2734,25 @@
! These are arrays of size ``NUM_OVERSHOOT_PARAM_SETS`` which is defined in
! ``star_data/public/star_data_def.inc`` (currently 16)

! For exponential overshoot: Parameters for exponential diffusive overshoot are described in the paper by Falk Herwig,
! "The evolution of AGB stars with convective overshoot", A&A, 360, 952-968 (2000).

! If you use the 'step+exponential', the step is placed first, after which the exponential is placed. Note that the
! parameterizations for both parts is still evaluated at the convective boundary (as described above), the exponential part
! is just displaced by the extent of the step part.
! This approach is motivated by works from
! Michielsen, M., C. Aerts, and D. M. Bowman. “Probing the Temperature Gradient in the Core Boundary Layer of Stars with Gravito-Inertial Modes. The Case of KIC 7760680.” Astronomy & Astrophysics 650 (June 2021): A175. https://doi.org/10.1051/0004-6361/202039926.
! Anders, Evan H., Adam S. Jermyn, Daniel Lecoanet, et al. “Schwarzschild and Ledoux Are Equivalent on Evolutionary Timescales.” The Astrophysical Journal Letters 928, no. 1 (2022): L10. https://doi.org/10.3847/2041-8213/ac5cb5.
! Anders, Evan H., Adam S. Jermyn, Daniel Lecoanet, and Benjamin P. Brown. “Stellar Convective Penetration: Parameterized Theory and Dynamical Simulations.” The Astrophysical Journal 926, no. 2 (2022): 169. https://doi.org/10.3847/1538-4357/ac408d.
! Johnston, Cole, Mathias Michielsen, Evan H. Anders, et al. “Modelling Time-Dependent Convective Penetration in 1D Stellar Evolution.” The Astrophysical Journal 964 (April 2024): 170. https://doi.org/10.3847/1538-4357/ad2343.

! The step overshoot part models convective entrainment, where the a convective
! zone "eats up" a ledoux stable region (typically above a convective core).
! The exponential overshoot part then models actual overshooting where inertia
! carries material beyond the Schwarzschild boundary.
! Note however that no temperature gradients are modified, MESA's implementation of overshoot
! only extends mixing regions (through the diffusion coefficients, ``D_mix``)

! ::

overshoot_D0(:) = 0d0
Expand All @@ -2761,7 +2778,6 @@

overshoot_mass_full_off(:) = 0d0


! overshoot_D_min
! ~~~~~~~~~~~~~~~

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4 changes: 3 additions & 1 deletion star/private/ctrls_io.f90
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Expand Up @@ -147,7 +147,7 @@ module ctrls_io
predictive_bdy_q_min, predictive_bdy_q_max, T_mix_limit, RSP_report_undercorrections, &
do_conv_premix, conv_premix_avoid_increase, conv_premix_time_factor, &
conv_premix_fix_pgas, conv_premix_dump_snapshots, do_premix_heating, &
overshoot_f, overshoot_f0, overshoot_D0, RSP_Qvisc_linear, dq_D_mix_zero_at_H_He_crossover, &
overshoot_f, overshoot_f2, overshoot_f0, overshoot_D0, RSP_Qvisc_linear, dq_D_mix_zero_at_H_He_crossover, &
overshoot_Delta0, overshoot_mass_full_on, overshoot_mass_full_off, dq_D_mix_zero_at_H_C_crossover, &
overshoot_scheme, overshoot_zone_type, overshoot_zone_loc, RSP_Qvisc_quadratic, &
overshoot_bdy_loc, overshoot_D_min, overshoot_brunt_B_max, mlt_gradT_fraction, max_conv_vel_div_csound, &
Expand Down Expand Up @@ -1125,6 +1125,7 @@ subroutine store_controls(s, ierr)
s% do_premix_heating = do_premix_heating

s% overshoot_f = overshoot_f
s% overshoot_f2 = overshoot_f2
s% overshoot_f0 = overshoot_f0
s% overshoot_D0 = overshoot_D0
s% overshoot_Delta0 = overshoot_Delta0
Expand Down Expand Up @@ -2848,6 +2849,7 @@ subroutine set_controls_for_writing(s, ierr)
do_premix_heating = s% do_premix_heating

overshoot_f = s% overshoot_f
overshoot_f2 = s% overshoot_f2
overshoot_f0 = s% overshoot_f0
overshoot_D0 = s% overshoot_D0
overshoot_Delta0 = s% overshoot_Delta0
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3 changes: 3 additions & 0 deletions star/private/overshoot.f90
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Expand Up @@ -25,6 +25,7 @@ module overshoot
use overshoot_utils
use overshoot_exp
use overshoot_step
use overshoot_step_exp

implicit none

Expand Down Expand Up @@ -170,6 +171,8 @@ subroutine add_overshooting (s, ierr)
! using the appropriate scheme-dependent routine

select case (s%overshoot_scheme(j))
case ('step+exponential')
call eval_overshoot_step_exp(s, i, j, k_a, k_b, D, vc, ierr)
case ('exponential')
call eval_overshoot_exp(s, i, j, k_a, k_b, D, vc, ierr)
case ('step')
Expand Down
48 changes: 18 additions & 30 deletions star/private/overshoot_exp.f90
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Expand Up @@ -70,12 +70,11 @@ subroutine eval_overshoot_exp (s, i, j, k_a, k_b, D, vc, ierr)
ierr = 0

! Extract parameters
f = s% overshoot_f(j)
f0 = s% overshoot_f0(j)

f = s%overshoot_f(j)
f0 = s%overshoot_f0(j)

D0 = s%overshoot_D0(j)
Delta0 = s%overshoot_Delta0(j)
D0 = s% overshoot_D0(j)
Delta0 = s% overshoot_Delta0(j)

if (f <= 0._dp .OR. f0 <= 0._dp) then
write(*,*) 'ERROR: for exponential overshooting, must set f and f0 > 0'
Expand All @@ -85,11 +84,10 @@ subroutine eval_overshoot_exp (s, i, j, k_a, k_b, D, vc, ierr)
end if

! Apply mass limits

if (s%star_mass < s%overshoot_mass_full_on(j)) then
if (s%star_mass > s%overshoot_mass_full_off(j)) then
w = (s%star_mass - s%overshoot_mass_full_off(j)) / &
(s%overshoot_mass_full_on(j) - s%overshoot_mass_full_off(j))
if (s% star_mass < s% overshoot_mass_full_on(j)) then
if (s% star_mass > s% overshoot_mass_full_off(j)) then
w = (s% star_mass - s% overshoot_mass_full_off(j)) / &
(s% overshoot_mass_full_on(j) - s% overshoot_mass_full_off(j))
factor = 0.5_dp*(1._dp - cospi(w))
f = f*factor
f0 = f0*factor
Expand All @@ -100,77 +98,67 @@ subroutine eval_overshoot_exp (s, i, j, k_a, k_b, D, vc, ierr)
end if

! Evaluate convective boundary (_cb) parameters

call eval_conv_bdy_r(s, i, r_cb, ierr)
if (ierr /= 0) return

call eval_conv_bdy_Hp(s, i, Hp_cb, ierr)
if (ierr /= 0) return

! Evaluate overshoot boundary (_ob) parameters

call eval_over_bdy_params(s, i, f0, k_ob, r_ob, D_ob, vc_ob, ierr)
if (ierr /= 0) return

! Loop over cell faces, adding overshoot until D <= overshoot_D_min

outward = s%top_conv_bdy(i)

outward = s% top_conv_bdy(i)
if (outward) then
k_a = k_ob
k_b = 1
dk = -1
else
k_a = k_ob+1
k_b = s%nz
k_b = s% nz
dk = 1
end if

! Loop over cell faces, adding overshoot until D <= overshoot_D_min
face_loop : do k = k_a, k_b, dk

! Evaluate the exponential factor

r = s%r(k)

r = s% r(k)
if (outward) then
dr = r - r_ob
else
dr = r_ob - r
end if

! Evaluate the exponential factor
if (f > 0._dp) then
factor = exp(-2._dp*dr/(f*Hp_cb))
else
factor = 0._dp
end if

! Store the diffusion coefficient and velocity

D(k) = (D0 + Delta0*D_ob)*factor
if(D_ob /= 0d0) then
vc(k) = (D0/D_ob + Delta0)*vc_ob*factor
else
vc(k) = 0d0
end if
! Check for early overshoot completion

if (D(k) < s%overshoot_D_min) then
! Check for early overshoot completion
if (D(k) < s% overshoot_D_min) then
k_b = k
exit face_loop
end if

end do face_loop

if (DEBUG) then
call eval_conv_bdy_r(s, i, r_cb, ierr)
if (ierr /= 0) return
write(*,*) 'exponential overshoot:'
write(*,*) ' k_a, k_b =', k_a, k_b
write(*,*) ' r_a, r_b =', s%r(k_a), s%r(k_b)
write(*,*) ' r_a, r_b =', s% r(k_a), s% r(k_b)
write(*,*) ' r_ob, r_cb =', r_ob, r_cb
write(*,*) ' Hp_cb =', Hp_cb
end if

return

end subroutine eval_overshoot_exp

end module overshoot_exp
43 changes: 15 additions & 28 deletions star/private/overshoot_step.f90
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Expand Up @@ -65,12 +65,11 @@ subroutine eval_overshoot_step (s, i, j, k_a, k_b, D, vc, ierr)
ierr = 0

! Extract parameters
f = s% overshoot_f(j)
f0 = s% overshoot_f0(j)

f = s%overshoot_f(j)
f0 = s%overshoot_f0(j)

D0 = s%overshoot_D0(j)
Delta0 = s%overshoot_Delta0(j)
D0 = s% overshoot_D0(j)
Delta0 = s% overshoot_Delta0(j)

if (f <= 0._dp .OR. f0 <= 0._dp) then
write(*,*) 'ERROR: for step overshooting, must set f and f0 > 0'
Expand All @@ -80,11 +79,10 @@ subroutine eval_overshoot_step (s, i, j, k_a, k_b, D, vc, ierr)
end if

! Apply mass limits

if (s%star_mass < s%overshoot_mass_full_on(j)) then
if (s%star_mass > s%overshoot_mass_full_off(j)) then
w = (s%star_mass - s%overshoot_mass_full_off(j)) / &
(s%overshoot_mass_full_on(j) - s%overshoot_mass_full_off(j))
if (s% star_mass < s% overshoot_mass_full_on(j)) then
if (s% star_mass > s% overshoot_mass_full_off(j)) then
w = (s% star_mass - s% overshoot_mass_full_off(j)) / &
(s% overshoot_mass_full_on(j) - s% overshoot_mass_full_off(j))
factor = 0.5_dp*(1._dp - cospi(w))
f = f*factor
f0 = f0*factor
Expand All @@ -95,68 +93,57 @@ subroutine eval_overshoot_step (s, i, j, k_a, k_b, D, vc, ierr)
end if

! Evaluate convective boundary (_cb) parameters

call eval_conv_bdy_Hp(s, i, Hp_cb, ierr)
if (ierr /= 0) return

! Evaluate overshoot boundary (_ob) parameters

call eval_over_bdy_params(s, i, f0, k_ob, r_ob, D_ob, vc_ob, ierr)
if (ierr /= 0) return

! Loop over cell faces, adding overshoot until D <= overshoot_D_min

outward = s%top_conv_bdy(i)

outward = s% top_conv_bdy(i)
if (outward) then
k_a = k_ob
k_b = 1
dk = -1
else
k_a = k_ob+1
k_b = s%nz
k_b = s% nz
dk = 1
end if

! Loop over cell faces, adding overshoot until D <= overshoot_D_min
face_loop : do k = k_a, k_b, dk

! Evaluate the step factor

r = s%r(k)

r = s% r(k)
if (outward) then
dr = r - r_ob
else
dr = r_ob - r
end if

! Evaluate the overshoot factor
if (dr < f*Hp_cb) then
factor = 1._dp
else
factor = 0._dp
end if

! Store the diffusion coefficient and velocity

D(k) = (D0 + Delta0*D_ob)*factor
if(D_ob /= 0d0) then
vc(k) = (D0/D_ob + Delta0)*vc_ob*factor
else
vc(k) = 0d0
end if
! Check for early overshoot completion

if (D(k) < s%overshoot_D_min) then
! Check for early overshoot completion
if (D(k) < s% overshoot_D_min) then
k_b = k
exit face_loop
end if

end do face_loop

ierr = 0

return

end subroutine eval_overshoot_step

end module overshoot_step
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