| Version 8 (modified by , 9 years ago) ( diff ) |
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Radiation feedback from sink particles
The amount of thermal radiation produced in the grid is a function of temperature. Since sinks are a subgrid model they themselves do not have temperature (we are not sure how big the forming star is, how fast it is growing by contraction, etc., so there isn't an easy way of assigning the sub-grid object a 'temperature'). Thus, we are left to estimate the amount of radiation produced by the sink by its accretion luminosity.
Since we do not track energy accretion onto the sink, we are left to assume gas that is accreted from the surrounding zones contribute to the accretion luminosity of the forming protostar, and thus we need a way to estimate this accretion luminosity. To do this, we will recycle some fraction of infalling energy back into the grid. This accretion energy () will be distributed smoothly in a kernel surrounding the sink every time step. It will then diffuse away from the sink via FLD radiative transfer. In this way, sinks will act as additional sources of radiation within the grid.
Accretion Luminosity
As discussed here, the following equation for the accretion luminosity:
should be a very good approximation for Astrobear to use.
Tracking accretion luminosity in the code
At each time-step i, the luminosity is computed as:
where is the mass of the sink particle at i, is the total accreted mass for that time-step, is the gravitational constant in computational units, is the radius of the star, taken to be 1 solar radius by default, but modifiable by the user at run-time, and is the hydro time-step. This luminosity is only computed after the sink particle has grown to have non-zero mass, and then will only be a source of luminosity after surrounding material has been deemed unstable and collapsing inward to the sink particle (i.e. is accreted).
