# TAC Meeting #2

## Thesis outline

• Protoplanetary disk chemical evolution
• Effect of accretion in a viscously-evolving protoplanetary disk (published 2020)
• Pebble drift with sublimation only
• Pebble drift + full chemistry
• Tidally distorted rocky planets
• Constraining the composition of USP planets in the Kepler sample (published 2020)
• Shapes of tidally-distorted transits and detectability
• Analytic Roche theory for modified polytrope planets

# Accretion paper

## Methods

• Iteratively compute the surface density that is consistent with RADMC temperature profile
• This is important because the temperature determines viscosity, which determines the surface density of the gas and, by extension, the dust, which again feeds back into the temperature
• Couple a chemistry solver to the interpolated physical properties of the gas and dust as they accrete

## Results

• Found that accretion can increase the abundances of some species (like hydrocarbons) by orders of magnitude in the inner disk!
• Cosmic ray chemistry also plays an important role, since cosmic-ray driven chemistry can produce intermediates that are then transported to the inner disk

## Caveats

• Applies to midplane only — how does vertical mixing affect these results?
• Gas and dust are well-coupled; can we relax that assumption?

# Pebble drift paper

## Lots of false starts!

• Smoothed particle hydrodynamics is too noisy, and is very complex in cylindrical coordinates
• Boundary conditions in two dimensions are non-trivial when we don't know the final solution a priori
• Solving benchmarking problems is much easier than solving even a simple alpha-disk

## Methods

• Physical model from Birnstiel+2010:
• One-dimensional disk surface density evolution equation
• Analytic prescription for dust velocity as a function of gas velocity
• Solve chemistry globally instead of locally with small water reaction network

## Equations

• Classic ssurface density evolution equation:

$\frac{\partial \Sigma}{\partial t} = \frac{3}{R} \frac{\partial}{\partial R} \left[R^{1/2} \frac{\partial}{\partial R} \left(\nu \Sigma R^{1/2}\right)\right]$

• Dust surface density evolution equation:

$\frac{\partial \Sigma_d}{\partial t} + \frac{1}{R} \frac{\partial}{\partial R} \left[R \left(F_\mathrm{diff} + F_\mathrm{adv}\right)\right] = 0$

## Assumptions and caveats

• The Lynden-Bell & Pringle equation assumes Keplerian gas, but the dust equation does not — slight inconsistency
• Static temperature power law, which is not realistic
• Could solve with flux-limited diffusion (this is likely more efficient, but more approximation)
• Do we expect a large difference?

## Possible direction: Cometary abundances

Using this model, could we explain certain “outlier” comets, such as 2I/Borisov, which have high CO-to-H2O ratios?

• Need realistic temperature structure
• Also may need stellar evolution to move the snowline

# Tidally-distorted planets paper

## Overview

• Used a relaxation method (originally proposed by Hachisu), modified to include a point-source star, to solve for planet properties in extreme gravitational fields
• Showed that KOI-1843.03 is likely iron-enhanced to have survived at its position near or at the Roche limit

## Methods

• Given:
• An equation of state for the core and mantle
• Pressure at center and core-mantle boundary
• Scaled separation from the star and axis ratio
• Use an iterative relaxation method to find self-consistent solutions (to a specified tolerance) for the planet density at all mesh points
• Planet properties cannot be specified in advance!

# Tidally-distorted transits paper

## Methods

• Using software I wrote, we have generated lots of planet shapes and their properties
• Want to take those shapes and determine what their transits look like, then correlate with properties
• Also want to explore the possibility of actually detecting distortion

## Current progress

• Machinery to raytrace transits is in place
• More recently, added higher-quality RNG for photon generation
• Outside software used: ISPC, TBB, Embree, OSPRay

## Open questions

• Can we constrain compositions from transit light curves?
• Or is the effect washed out by limb darkening of the host star?
• How do we correlate properties with transit shapes?

# Future plans

## Conferences and talks

• Last summer: Invited speaker, PETSc users meeting
• Upcoming:
• Astrochemical Frontiers (virtual meeting, will submit abstract by May 18)
• Heidelberg summer school on planet formation in protoplanetary disks (application due by June 1, but will university travel be allowed by August?)

## Suggested timeline

• End of summer 2020: First pebble drift paper
• End of fall 2020: Tidally-distorted transits paper
• End of spring 2021: Second pebble drift paper