This code requires several modules from the publicly-available SPH code Phantom. This means there are two ways to install this code, depending on whether or not you already have Phantom on your machine.
You don't have to install Phantom separately. Phantom has been incorporated as a git submodule to this repository. This means that this repository stores a copy of the Phantom repository, but the commit history of Phantom is independent from this code's. To clone this repository including the Phantom submodule, you must include the --recurse-submodules flag:
git clone --recurse-submodules [email protected]:themikelau/flat-entropy-star.git
You should see that the flat-entropy-star repository contains a copy of phantom.
If you already have Phantom on your machine, clone this repository with the usual command, without the --recurse-submodules flag shown above. But then, you need to create a soft link to Phantom. If PHANTOM_DIR is the path to your Phantom directory, execute the following from the flat-entropy-star directory:
ln -s PHANTOM_DIR phantom
A word of caution: There is no guarantee that whatever version of Phantom you have is (backward) compatible with this code. If you run into compilation or runtime errors, you should try checking out the Phantom version with commit hash 5d3911c. If there are further issues, feel free to contact me.
Before compile the code, you should set up your calculation by editing fixed_S_profile.f90. Calculation settings are specified by editing part of the calc_rho_and_pres subroutine:
!-----------------------------------------------------------------------------------------
! USER SETTINGS
!-----------------------------------------------------------------------------------------
!
! Choose total stellar mass (including core particle)
Mstar = 12.0 * solarm
!
! Choose number of zones
N = 10000
!
! Choose core mass
mcore = 3.84048 * solarm
!
! Choose core radius
rcore = 18.5 * solarr
!
! Choose desired stellar radius to shoot for
Rstar = 4.3061478138863500d13
!
! Desired surface pressure
surfpres = 300.
!
! Adjustment factor for shooting
rhofac0 = 0.01 ! Multiplicative factor for adjusting central density
Sfac = 0.008 ! Additive factor for adjusting entropy
tol = 1d-3 ! Relative tolerance for matching surface pressure and radius to desired values
!
! EoS options
ieos = 12
ientropy = 2 ! Include both gas and radiation entropy
gamma = 5./3. ! Polytropic index
gmw = 0.61821 ! Assumed mean molecular weight
!-----------------------------------------------------------------------------------------
In a nutshell, specify the stellar mass, stellar radius, core mass, and core radius. An outer boundary condition is specified as the surface pressure, which should not be "too high" to avoid expansion. You should also specify EoS-related settings: ieos (equation of state type, following what Phantom uses), ientropy (see the entropy function in Phantom's eos module), gamma (polytropic index), and gmw (mean molecular weight, assumed to be constant throughout star).
You may also adjust initial guesses for the central density and fixed value of specific entropy. Play with these values if the code is struggling to converge onto a solution:
!-----------------------------------------------------------------------------------------
! INITIAL GUESSES
!-----------------------------------------------------------------------------------------
!
! Central density
rho(0) = 7.607091d-5
!
! Central pressure
pres(0) = 2.831573d10 ! Isn't actually used
!
! Constant value of entropy
Sc = 4569322041.73678
!-----------------------------------------------------------------------------------------
To compile the code, simply type
make fixedSprofile
Hopefully this is successful, and you should now have the executable fixedSprofile, which can be run by typing
./fixedSprofile
You must delete fixedSprofile and recompile every time you tweak the settings in fixed_S_profile.f90.