12/2017: AGU Fall Meeting in NOLA
The 2017 Fall Meeting of the American Geophysical Union took place in New Orleans, LA in mid-December. As you can see in the picture, I presented some preliminary research I am doing with Prof. Paul Withers here at BU. Each of those 20 panels on my poster are electron density profiles from the ionosphere of Titan–Saturn’s largest moon! The profiles were inferred from radio occultation observations made by the Radio Science Subsystem onboard the Cassini Spacecraft. During a radio occultation, Cassini sends a radio signal to the Earth that is picked up by the Deep Space Network (DSN), which is a collection of gigantic radio dishes spread around the world. Check out the DSN website out of JPL that shows (in real time!) what spacecraft each station is communicating with. As the line of sight of the radio signal between the DSN and Cassini dips into the ionosphere of Titan, the presence of electrons alters the radio signal ever so slightly. To be specific, the electrons result in the radio waves experiencing a gradient in the index of refraction (I’m a sucker for a project involving atmospheric refraction), which alters the phase of the radio signal measured by DSN. Add in some mathematics and out comes an electron density profile. Over the course of the Cassini Mission, the ionosphere of Titan showed some interesting features, which still need to be explored in more detail. I hope to get these profiles up on NASA’s Planetary Data System soon, so the whole community can access them. Also, keep an eye out for a paper describing our radio analysis process…
09/2017: RETrO and the Stellar Mirage Paper Are Out!
It’s been a busy summer but I finally finished my sole-author theory project investigating atmospheric refraction in transiting exoplanets. I conducted this study using a custom ray tracing code to simulate how refraction creates mirages in exoplanetary atmospheres outside of transit. This code is titled Refraction in Exoplanet Transit Observations, or RETrO (check it out on github!). In the figure to left, the colorful lines are individual rays being traced (backwards) from an observer off to the right, through the planetary atmosphere, and back to the star off to the left. In total, I modeled over 82,000 exoplanetary systems, and each required ~100 rays. That means ~8 million rays and tens of millions of equations solved, and that’s just for the ray tracing alone! Thankfully, I had access to Boston University’s Shared Computing Cluster at the Massachusetts Green High Performance Computer Center, which accelerated the process.
Also take a look at the talk I gave on this work for the BU Astronomy Department Student Seminar Series.
05/2017: Teaching Award!
I was recognized as the 2016-2017 Outstanding Teaching Fellow in the Department of Astronomy by the Graduate School of Arts and Sciences at BU! I received this for my work in the undergraduate course AS107: Life Beyond Earth with Prof. Thomas Bania. After we taught this course in Fall 2016, it was listed as ones of BU’s Top 10 Epic Courses by BU Today. It is a fascinating class to be part of, and I was honored to receive this award.
12/2016: Phantom Stars in the Kepler Dataset!
I led a team of researchers that recently discovered a phantom star—present in the Kepler Input Catalog (KIC) and the Kepler pipeline but not an actual star—in the Kepler dataset. The discovery came about after an observing run of three transits of the supposed super-Earth exoplanet Kepler-445c at the Discovery Channel Telescope. The planetary and stellar properties of Kepler-445c and its host star were thought to be similar to GJ 1214b, so it was an enticing target for follow-up atmospheric characterization. However, the planetary radius returned from the initial characterization of the Kepler transit observations was flawed because a phantom star incorrectly diluted the transit depth. Now, we find that the radius of Kepler-445c is ~1.6 times that of the Earth, making it very difficult to tell if it is a rocky or gaseous exoplanet! We posit that the phantom star came to be after an error in an old stellar catalog propagated into the KIC and through the pre-data conditioning in the Kepler pipeline.
The good news is that phantom stars are likely rare in the Kepler dataset. Plus, a recent update to the Kepler pipeline should prevent against similar issues in the future. However, problems from stellar magnitude and position errors in old star catalogs may certainly arise in the dataset from the upcoming Transiting Exoplanet Survey Satellite (TESS) mission. The pixels on the TESS detectors will be ~5 times larger than those that flew on Kepler, making stellar crowding and transit dilution a serious concern!