Undergraduate work at USC

The summer after my sophomore at The University of Southern California in 2009 I started doing research with Edward Rhodes in Helioseismology. I worked every semester and summer after that until September 2011. I learned valuable coding skills and gained experience working with a team. I attended two poster sessions and a week long heliophysics workshop at Stanford Universtiy.

Graduate work at UC Santa Barbara

I started working with Lars Bildsten in May of 2012. I was a teaching assistant and took graduate classes until June 2014. I have produced six first-author papers and have coauthored three additional papers, with collaborators from Caltech, UC Berkeley, UC Santa Cruz, and Bonn University. I graduated in August of 2017 with both a Masters degree and a PhD in Physics.

I have attended conferences at UCLA, Caltech, UC Berkeley, Texas A&M University-Commerce, Columbia University, and University of Warwick.

I have been a teaching assistant at every annual MESA Summer School since it's inception in 2012, where we invite graduate students and post-docs from all around the world enroll in a week long course of lectures and lab-exercises designed to exhibit a subset of the many features of the stellar evolution code MESA so they can utilize it in their own research.

Below is a list of my publications from my time at UC Santa Barbara.

Fast and Luminous Transients from the Explosions of Long Lived Massive White Dwarf Merger Remnants

December 2017

Most of my papers focus on stable mass transfer between compact binary stars, but this paper explores the outcome of a merger of binary white dwarf stars that avoid immediate explosive outcomes. We show how these sorts of merger remnants evolve with large, extended envelopes (above 400 solar radii) and compact cores that grow in mass. Once the cores reach the Chandrasekhar mass, they collapse to neutron stars and generate shocks in the envelope, similar to core collapse supernovae. The main difference to core collapse supernovae is that in the explosions studied in this paper have lower envelope masses, leading to shorter light curves (about a week long) and higher velocities (about 10,000 km/s). These simulations match several properties of a new observed class of rapidly evolving and luminous transients.

The OmegaWhite survey for short-period variable stars - V. Discovery of an ultracompact hot subdwarf binary with a compact companion in a 44 minute orbit

December 2017

This particular binary star system was discovered by the OmegaWhite survey, which is is a high cadence synoptic survey of the southern Galactic Plane and Galactic Bulge, the main aim of which is to identify ultracompact binaries using the VST telescope at the European Southern Observatory’s (ESO) Paranal site in Chile. Optical photometric and spectroscopic followup was carried out using several telescopes, including the SAAO 1.9-m Telescope with SHOC and Keck/LRIS. We found that the system contains a low-mass sdO star in a 44 minute orbital period binary with a high-mass WD companion. Using MESA, I constructed several models of sdO stars attempting to match the measure properties of the observed star and make predictions of the future for this binary star system. We concluded that a sdO star with 32% the mass of the sun was a the best fit to the observations, and that the two stars will make contact in approximately 17.6 million years at an orbital period of 5 minutes.

HD 49798: Its History of Binary Interaction and Future Evolution

September 2017

My collaborator, Thomas Kupfer of Caltech, brought this star system to our attention, as it similar to systems we had studied in the past: an intermediate mass helium star in a tight binary with a compact object. There is a 13 second period X-ray pulse coming from the compact companion. Previous studies of this binary had disagreed as to whether the compact companion is a white dwarf or a neutron star. In this paper, we give our own interpretation of the system, including the nature of the compact companion, and use MESA to predict the future of this binary star.

Accretion-Induced Collapse From Helium Star + White Dwarf Binaries

June 2017

This paper is similar to my paper about C/O WDs accreting and steadily burning helium, but in this paper we consider higher mass WDs that are composed primarily of oxygen and neon (O/Ne WDs). When these stars grow to the Chandrasekhar mass, instead of exploding from runaway carbon burning in the core, these stars collapse to neutron stars. Here we describe the growth process and likely profiles of these stars just prior to collapse.

PTF1 J082340.04+081936.5: A hot subdwarf B star with a low mass white dwarf companion in an 87 minute orbit

December 2016

I collaborated with Thomas Kupfer of Caltech, the lead author on this paper, to provide predictions for the future of an observed white dwarf + helium star binary system based off of computer simulations I carried out using MESA.

Convection Destroys the Core/Mantle Structure in Hybrid C/O/Ne White Dwarfs

November 2016

A hybrid C/O/Ne white dwarf is a compact remnant star where the inner 20-40% of the core is primarily carbon and oxygen (C/O), surrounded by a mantle of oxygen and neon (O/Ne). Astrophysicists who do 3D simulations of stellar explosions like to use models of hybrid white dwarfs because they have high masses and plenty of carbon at the center to ignite an explosion. In this paper, we show that the C/O core and O/Ne mantle structure is unstable to mixing very soon after formation, which mixes the carbon outwards from the center, changing ignition conditions, or possibly preventing an ignition all together.

Carbon Shell or Core Ignitions in White Dwarfs Accreting from Helium Stars

April 2016

This paper adds to the theoretical knowledge of the single degenerate channel for Type Ia Supernovae. Physicists use the predictable luminosites of Type Ia Supernovae to determine the distances to galaxies and quantify the expansion of the universe. The physical mechanism of producing the progenitors to Type Ia Supernovae is still not well understood. Here we explore the single degenerate channel and show that helium star + white dwarf binary systems can lead to Type Ia Supernovae, but if the helium star mass is too high, nuclear carbon burning will ignite near the surface of the white dwarf, instead of the center, preventing an explosion. This paper explores only one of the possible progenitor channels to Type Ia Supernovae.

AM Canum Venaticorum Progenitors with Helium Star Donors and the Resultant Explosions

July 2015

Low mass helium stars that are just massive enough to undergo core helium burning are called sub-dwarf B stars (sdBs). Binary systems with a white dwarf and an sdB star that have orbital periods of about an hour or less can undergo mass transfer from the helium star to the white dwarf slowly enough to build up thick, cold helium layers. When these helium layers become dense enough from compression, nuclear helium burning ignites and ejects the entire accreted layer. These shell explosions can be up to 10% the brightness of a Type Ia Supernovae, but may not disrupt the underlying white dwarf. If the system survives such shell explosions, it may end up as a stable AM Canum Venaticorum system

Hydrogen Burning on Accreting White Dwarfs: Stability, Recurrent Novae, and the Post-nova Supersoft Phase

November 2013

A fellow grad student, Bill Wolf, who also worked with Lars Bildsten, asked for some assistance on this paper, and I helped him out by running some MESA simulations. In this paper we studied the range of hydrogen-rich accretion rates onto white dwarfs where steady burning was possible, and lower accretion rates where recurrent novae occur. We also discuss the observational properties of such objects.