Notes related to the 49 Ceti project...
Background:
49 Ceti is a gas-rich debris disk that was recently resolved by ALMA at unprecedented angular resolution and sensitivity. My senior thesis involved modeling these data in order to better understand the processes that shape planet formation. We find that the dust disk of 49 Ceti is unlike anything observed before. It has two distinct regions, with an inner disk characterized by small, ~0.1 micron grains, whereas the outer belt is characterized by larger, ~2.0 micron grains. The disk increases in surface density to a peak around 110AU before falling off thereafter. We think this region of higher density in the dust corresponds to a similar increase in the gas surface density, but models have thus far been inconclusive.
For information about the modeling process, please see this repository.
Data presentation:
49Ceti_dataPlots.py takes 49Ceti_.75arcsectaper.fits and 49Ceti_robust2.fits as inputs and creates 49Ceti_dataPlots.png as output. The color maps used are custom in order to appear continuous in color and greyscale. It could be easily edited to take different data images if desired.
What is responsible for the peak in surface density?
49Ceti_plotStirring.py generates a plot (49 Ceti_plotStirring.png) of the eccentricity needed for a hypothetical planet in semi-major axis/mass space in order to "stir" the planetesimal belt at 110AU. Debris rings need something to jostle them to continually replenish the small dust grains we observe. 49 Ceti's disk is not massive enough to have "self-stirred" this ring in the age of the system, and the only other option is planetary stirring. Using formulas from Mustill & Wyatt (2009), we are able to get a sense of the combination of the eccentricity/mass/semimajor necessary to stir the ring. One such example is that a Jupiter-like planet (eccentricity ~ 0.05, mass ~ 1M_Jup) would need an orbit with a semimajor axis of 40AU to stir the ring. See the plot below for all possible combinations of parameters.
Surface Density Distribution
49Ceti_surfaceDensityPlot.py calculates the median surface density plus/minus 1sigma for each type of model- the single power law (SPL), double power law (DPL), and single power law with ring (SPLWR) and plots it (49Ceti_surfaceDensity.png). It does this by randomly grabbing walkers and their corresponding disk parameters from the MCMC chain after the burn-in phase has been completed, calculating the surface density for each walker every 0.1AU, then determining the distribution of surface densities at each radius over all the models. We plot the median of the surface density for each model plus/minus 1sigma. The dotted lines denote where the surface density is not actually resolved by our modeling-- that the surface density falls off proportional to r^{-1} in the inner disk is an assumption in our model.
