Research Interests and Projects

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I am studying Type Ia Supernovae (SNe Ia) under the advising of Dr. Mark Leising at Clemson University Physics and Astronomy. I am also working closely with Dr. Peter Milne at University of Arizona Steward Observatory.

Below is a brief overview of my research plans, which include observing SNe Ia in optical and near-IR wavelengths with 4m-class telescopes at late epochs (greater than 200 days) in an effort to construct an accurate (and bolometric) picture of the power deposition and positron escape.

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Research Plans

The use of type Ia supernovae (SNe Ia) as distance indicators has revolutionized cosmology, but these standard candles are not as "standard" as we once thought. SNe Ia are believed to be the result of a white dwarf that accretes mass from a binary companion until it nears the Chandrasekhar mass limit and undergoes thermonuclear explosion. Because SNe Ia all explode with similar masses, they were thought to have the same intrinsic brightness. However, groups have observed high redshift SNe Ia that are dimmer than expected indicating an accelerating expansion of the universe and implying the existence of dark energy. Much is still not understood about these standard candles. Peculiar super-luminous and sub-luminous SNe have been discovered, each having spectra atypical of normally luminous SNe Ia. Currently there is no agreed upon theory that accounts for a difference in luminosity among SNe. If we are to draw such profound conclusions from these objects, it is crucial that we understand what is causing such differences.

Observationally, SNe brighten quickly and then dim slowly. This slow dimming is due to the gradual decay of radioactive 56Ni formed from the nuclear flame propagating through the star. The 56Ni --> 56Co --> 56Fe decay emits gamma rays and positrons that power the light curve. Certain theories try to explain the differing luminosity (classes) seen in SNe Ia through explosion scenarios that produce greater or lesser amounts of radioactive 56Ni. Some models claim it is the depth at which 56Ni is produced that accounts for the difference in luminosity 4, while others suggest it is due to the progenitor system (i.e., two white dwarfs colliding). SNe light curves will provide an excellent tool to determine what is actually occurring. At early times (0-100 days after max light) the ejecta from the explosion are optically thick, and all gamma rays from the decay are absorbed. As the ejecta expand, however, photons progressively deeper in the ejecta are able to escape. After ~300 days the ejecta are transparent to the gamma rays, and the light observed is predominately from the center, where nuclear burning occurred. Additionally, as the supernova (SN) cools, a larger portion of the light is emitted in the infrared.

Until recently, people assumed that the bolometric light curve closely followed that of the optical bands. Thus, while an increasing number of observed SNe have well-sampled early light curves, there are only a handful that have been studied at late times in the infrared. Some of these light curves have been surprisingly bright, but there is little consistency. This view deep into SNe at late times is crucial to our understanding of SNe Ia.

By carefully monitoring the apparent magnitude of these SNe, I will be able to deduce the input power and be able to answer questions such as how much and where radioactive 56Ni is produced, how quickly the ejecta are expanding, what the progenitor system is, and determine the reason for the difference in luminosity class.

I will model the transport of gamma rays from decaying 56Ni and 56Co as they first are trapped by, and later escape, the expanding ejecta. From this model, I can produce a truly bolometric SN Ia light curve (which includes the infrared) for a given set of parameters. In this way, I will determine which initial conditions correlate with which SN luminosity class.