Star Particle Class¶
To give star particles more functionality and interaction with the grids, it was useful to create a new class for a generic particle type that can represent, e.g., stars, black holes, sink particles.
- conversion to a radiation source
- adding feedback spheres to the grid, e.g. mass removal from accretion, supernovae.
- different behaviors for different star types
- multiple types of star particles
- “active” and “inactive” stars
We keep the original implementation of the particles that are stored
in the pointers,
ParticleAttribute. Star particles are still created in the FORTRAN
star_maker2.F. In the current version, the star
class is a layer on top of these particles. Thus we must keep the
particle pointers and objects synchronized when their quantities
Particles created in the FORTRAN routines that will be converted into
a star object initially have a negative particle type. This indicates
that the star is not “born” yet, which is also used to flag various
feedback spheres, such as mass removal from the grid. The stars are
activated, i.e. positive particle type, in
after it has been checked for mergers, accretion, and feedback.
We store the star objects as a linked list in grid class. Because a star object can affect multiple grids (over multiple processors) when adding feedback sphere, processors other than the one hosting the star particle needs to know about this star object. Currently for convenience, we create a global list of star objects on all processors. For not many stars (< 100k), this does not consume that much memory. However in the future, we might have to reconsider how star particles are communicated across processors.
Any event can be set in
Star::SetFeedbackFlag to add a feedback
sphere. This sphere can be of any size, and its properties are set in
grid::AddFeedbackSphere(). Because they can cover grids on
multiple levels, we have to ensure that they are all at the same
Star::FindFeedbackSphere(), we check if sphere is
completely contained within grids on the current level. If true, we
can safely add the sphere. If it’s not imperative that the grids are
completely synchronized, one can add the feedback sphere immediate
after the star object is flagged for feedback.
Accretion / Mass Loss¶
Star objects can store up to 100 (
#define MAX_ACCR) accretion
rates as a function of time. Alternatively, currently in the black
hole particles, they can have an instantaneous accretion rate. This is
Star::CalculateMassAccretion. The actual accretion to the
star object is done in
How to add a new particle type¶
Set the particle type to the negative of the particle type in the star maker routine. Be sure not to overwrite the type like what’s done in the regular
Add the particle type to the if-statement in
Then the particles merge if any exist within
StarClusterCombineRadius. This is not restricted to only star cluster (radiating) particles. Even if there is any merging, the particle shouldn’t disappear.
At the end of
StarParticleInitialize(), the routine checks if any stars should be activated in
Star_SetFeedbackFlag. This is where you should check first for errors or omissions. You’ll have to add a new case to the switch statement. Something as simple as
case NEW_PARTICLE_TYPE: if (this->type < 0) this->FeedbackFlag = FORMATION; else this->FeedbackFlag = NO_FEEDBACK;
After this, the particle is still negative but will be flipped after the feedback to the grid is applied in
Star_ActivateNewStar()that’s called from
StarParticleFinalize. Here for Pop II and III stars, we use a mass criterion. For Pop III stars, we set the mass to zero in the
pop3_maker()f77 routine, then only set the mass after we’ve applied the feedback sphere.
The grid feedback is added in
StarParticleAddFeedbackthat is called in
Star_CalculateFeedbackParameters(), you’ll want to add an extra case to the switch statement that specifies the radius of the feedback sphere and its color (metal) density.
If the feedback sphere is covered by grids on the level calling
StarParticleAddFeedback()(i.e. all of the cells will be at the same time), then
Grid_AddFeedbackSphere()will be called. Here you’ll have to add another if-block to add your color field to the grid.