[Users] GRHydro_InitData - magnetic fields - neutron stars

[Daniel Gerlicher]

Hi!

I have a question regarding the initial data thorn of GRHydro.
The documentation and ccl files didn't really help me.

The following was taken from paper [1] and now I am trying to add
magnetic fields to the stars.

My questions are:

1) What are the units of (A) and (B) below? Is the following conversion
factor correct?
The star should have a field strength of 10^16 Gauss.
Using the following conversion would give "0.00011973228161339154" for
(A) and (B).

2) What are reasonable values for (C..F)? Can I just use the default
ones given in param.ccl?
Is there a reason not to use the default ones?
My plan is to analyse the structure of the field after the collapse and
the influence on the wave signal.

> # constants, in SI
> G     = 6.673e-11       # m^3/(kg s^2)
> c     = 299792458       # m/s
> M_sun = 1.98892e30      # kg
> mu0   = 1.2566370614e-6 # Newton/Ampere^2
> Kb    = 1.3806488e-23   # Joule/K
> Mparsec = 3.08567758e19 # km
> CU_to_Tesla = c**4 / M_sun / G**(1.5)* mu0**(0.5)
> CU_to_Gauss = c**4 / M_sun / G**(1.5)* mu0**(0.5) * 10000
> #-------------------------------------------------
> # Magentic Fields:
> #-------------------------------------------------
> (A) GRHydro_InitData::poloidal_A_b_1      = 0.00011973228161339154
> (B) GRHydro_InitData::poloidal_A_b_2      = 0.00011973228161339154
> (C) GRHydro_InitData::poloidal_P_cut_1    = 3.72e-6 #Non è in
> percentuale!!
> (D) GRHydro_InitData::poloidal_P_cut_2    = 3.72e-6 #Non è in
> percentuale!!
> (E) GRHydro_InitData::poloidal_n_p = 1 #Esponente di max((rho-rho_cut),0)
> (F) GRHydro_InitData::poloidal_P_p = 2 #Esponente di max((P-P_cut),0)
> GRHydro_InitData::Xc_1 = -13.5
> GRHydro_InitData::Xc_2 = 13.5
> GRHydro_InitData::Yc_1 = 0.0
> GRHydro_InitData::Yc_2 = 0.0
> GRHydro_InitData::Zc_1 = 0.0
> GRHydro_InitData::Zc_2 = 0.0

3) These should be fine, right?

> GRHydro::transport_constraints     = "yes"
> GRHydro::track_divB                = "yes"
> GRHydro::calculate_bcom            = "yes"
> #GRHydro::clean_divergence            = "no"
> GRHydro::Grhydro_MaxNumConstrainedVars = 33
> GRHydro::GRHydro_MaxNumEvolvedVars     = 10
>
> HydroBase::initial_Bvec       = "bin_ns_poloidalmagfield"

The field is evolved and everything seems okay, I am just not sure about
the units and (C..F).

4) Is there a good method to visualize the B-field?
Visit + Carpet hdf5 reader + Streamlines? (seems to be "buggy")

Thank you!

Best regards,
Daniel

References:
[1] "R. De Pietri, A. Feo, F. Maione, and F. Löffler, “Modeling Equal
and Unequal Mass Binary Neutron Star Mergers Using Public Codes,” Phys.
Rev., vol. D93, no. 6, p. 064047, 2016."