I am a fourth year graduate student in Harvard University's Astronomy and Astrophysics department working with Mercedes López-Morales on exoplanet atmosphere characterization. When not lurking on Stack Overflow or participating in science outreach, I like rowing on the Charles river for our grad school's crew team and looking for free pizza.
Particle Trajectory Code
Zero Energy Loss
This is an ideal particle trajectory calculated according to the binary system's Roche Potential. The solution was iterated with an RK4 integrator. The initial conditions were set with a thermal velocity at L1, angled towards the accretor (in orange) with an angle determined by the system's mass ratio (see equation 24 of Lubow and Shu 1974).
Artificial Energy Loss
Here is the same setup, but with artificial energy loss every time step. This was done to mimic the energy that is lost to shocks and other collisions in real fluid interactions. This was done by having the test particle lose energy while maintaining its angular momentum. I also added a little kick in the z component of the particle's initial velocity to make it a little more fun to watch.
This is a top down plot of the same code applied to WASP-12/b (to scale). I waited until a full orbit to turn on the artificial energy loss to mimic on full lap of the accretion stream before colliding with itself. The corners due to the Coriolis force are clearly scene and the orbit settles down into its circularization radius (in green), as predicted from angular momentum conservation.
Sedov Test Case
Example test case of evolving Sedov explosions in FLASH. I added two, then three, explosions to visualize how the code handles shocks and reflection boundary conditions. An interesting thing to note is that vorticity is conserved; there are as many counter-clockwise vortices as clockwise ones at all times.
This code was then applied to WASP-12/b in a 2D setup. Essential, the massless test particle in the ballistic particle code was replaced with a fluid outflow boundary with properties adopted from Lai et al 2010. I then added an artificial ramp up in density at around the 5 day mark to effectively fast-forward the disk to a more evolved state.
The same FLASH simulation was adapted to 3D to create the image above. This is an isodensity contour plot taken part way through the simulation. The location of L1 can be seen as the orange-yellow sphere towards the bottom left. These simulations were used to create virtual light curves to compare with observations from HST's Cosmic Origins Spectrograph.
0.6 Solar Mass WD
Top: Time series of density vs. temperature profile. Flattening towards high densities due to degeneracy pressure supporting the core of the white dwarf can start to be seen.
Bottom: A summary of different elements present, where xq is 1 minus the fraction of the total star mass interior to the outer boundary of each zone.
Solar Mass White Dwarf
Top: Calculated HR diagram with major regimes labeled.
Bottom: Time evolution of different elements by mass fraction. The entire simulation ran for about 10 billion years, but only about the last 200 million years is shown above.
15 Solar Mass WD
Top: Central temperature vs. central density plot. The green section shows how far the code was able to be pushed before hitting convergence errors.
Bottom: Mass coordinate vs log abundance plots for each stage of the massive white dwarf's evolution