[Mesa-users] Loss of angular moment

[Roque Caballero Navarro]

Dear all,

   I'm trying to implement a magnetic braking routine based on Matteo Cantiello exercise propose during the Mesa school 2012 (here the details<http://cococubed.asu.edu/mesa_market/ewExternalFiles/2012_cantiello.zip>.) Well, for doing it I'm using the hook other_torque and the code is implemented, as usual, in the run_extras_star.f file. Below you can see the core part of the implementation:

  1.           if (s% use_other_torque) then
  2.
  3.              !Star data
  4.              r_st = s% r(1)
  5.              m_st = s% m(1)
  6.              omega_surf = s% omega_avg_surf
  7.              m_dot = s% star_mdot
  8.
  9.              v_esc = 618 * (((Rsun/r_st)*(m_st/Msun)))**0.5
  10.
  11.             v_inf = 1.92 * v_esc
  12.
  13.             B = s% x_ctrl(6)
  14.
  15.             eta_surf = abs(((r_st/Rsun)**2/B**2)/(m_dot * v_inf))
  16.
  17.             j_dot = two_thirds * m_dot * omega_surf * (r_st/Rsun)**2 * eta_surf
  18.
  19.             s% extra_jdot(1) = j_dot
  20.             !s% extra_jdot(1) = -1
  21.
  22.             if (debug_use_other_torque) then
  23.                write(*,*) "Rsun=", Rsun, "Msun=", Msun, "r_st=", r_st, "m_st=", m_st, &
  24.                   "v_esc=", v_esc, "v_inf", v_inf, "B", B, "m_dot", m_dot, "eta_surf", eta_surf, &
  25.                   "omega_surf", omega_surf, "j_dot", j_dot
  26.             end if
  27.
  28.             s% x_ctrl(7) = v_esc
  29.             s% x_ctrl(8) = v_inf
  30.             s% x_ctrl(9) = eta_surf
  31.             s% x_ctrl(10) = j_dot
  32.             s% x_ctrl(11) = m_dot
  33.
  34.          end if

The input parameters for the calculation are the radius, mass, loss of mass and velocity at surface (lines 4 to 7). After some calculations, I end up with a loss of angular moment j_dot which I pass back using the array extra_jdot (line 20). After running a simulation with this routine activated, I'd expect to have lower values of velocity at surface but I couldn't find any difference. I've even assigned an unreal value (line 20) to the extra_jdot array but nothing changed. So, something must be wrong or missing in the implementation. As you maybe has already noticed, I'm just providing a value to one cell, the outermost  one. I'm assuming that only this layer is affected by the magnetic braking effect.

As usual, any help is more than welcome.

Kind regards,

Roque





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