Previous Research (website now archived)

I am interested in the formation and migration histories of giant planets. These giant planets are found on orbits as close as 0.01 astronomical units (au) and as far as hundreds of au. My work involves direct imaging techniques to investigate giant planet dynamics.

Imaging giant planets around young stars

Giant planet formation may be enhanced near their star system's ice line. In the protoplanetary disks, temperatures decrease with distance from the star, and the location where the temperature is cool enough for ice to form is known as the ice line. This creates an increase in the density of solid materials, which may help to form giant planets.

I am collaborating with Dimitri Mawet on a search for giant planets around a sample of 200 young M-stars. We are using a vortex coronagraph, a specialized piece of equipment that allows us to block out the star's light in order to see the very faint giant planet companion. Our initial survey is complete and we are working on follow-up efforts to verify candidate companion objects.

HR8799, a famous directly imaged planetary system

NRC-HAA, C. Marois, and Keck Observatory

An image of HR8799, a famous directly imaged plaentary system.


Previous Research

Artistic rendering of Upsilon Andromedae b


An artistic depiction of the hot Jupiter named Upsilon Andromedae b.

Friends of hot Jupiters poster presented at Exoplanets I

My poster summarizing our project's main results. Click on the thumbnail above to get the poster in PDF form.

LA Times story image

Click here to read the LA Times' coverage of this work

Friends of Hot Jupiters

Hot Jupiters are Jupiter-sized planets that orbit extremely close to their host star. Some of these planets have orbits that are misaligned with respect to the star's spin axis and/or have non-zero orbital eccentricities, suggesting that it may have interacted with other objects in the system, such as another planet or a star ("friends").

With my PhD advisor, Heather Knutson, I have led a direct imaging survey using Keck NIRC2 to look for stellar companions around hot Jupiter host stars. In 2015, we published our initial results, showing that there is no correlation between misaligned hot Jupiters and the presence of a stellar companion. In 2016, we use the properties of the entire stellar companion population to determine that less than 20 percent of hot Jupiters have stellar companions capable of inducing Kozai-Lidov migration. We also found that hot Jupiter host stars are three times more likely to have a stellar companion with separations between 50-2000 AU than field stars, suggesting that binary star systems may create environments that favor giant planet formation.

We have published our results in the following papers:
Friends of hot Jupiters II, Ngo et al. (2015), ApJ, 800, 138.
Friends of hot Jupiters IV, Ngo et al. (2016), ApJ, 827, 8.

In July 2016, I presented a summary of this project as a poster at Exoplanets I meeting in Davos, Switzerland. Click on the preview to the left to get the full PDF.

The LA Times covered our results in this story.

In a follow-up study, we searched for companions around RV-detected giant planet systems. We found that in these systems, there was some evidence for important planet-planet dynamical interactions but no evidence for star-planet dynamical interactions. These results are published in the following papers:
Planetary companions: Bryan et al. (2016), ApJ, 821, 189.
Stellar companions: Ngo et al. (2017), AJ, 153, 242.


Searching for Distant Relatives of Sedna

Sedna is a minor planet discovered by Mike Brown, Chad Trujillo, and David Rabinowitz in 2003. Its distance (see figure) and very eccentric orbit suggest that its origin may not be in the Kuiper Belt.

Mike Brown and I conducted a survey in 2013 to search for other distant objects in between the Kuiper Belt and Sedna. We hope additional discoveries (or non-discoveries) of Sedna's relatives (similarly distant objects) can lead to better constraints on ideas about Sedna's and our Solar System's origin.

Sedna's orbit is extremely distant and eccentric

NASA/JPL-Caltech/R. Hurt

Sedna's orbit, in red, to scale with the orbits of the giant planets (other circles of various colours).

Artistic rendering of the early Solar Nebula

In the core accretion model, planets form through two body accretionary collisons in a protoplanteary disk (depicted in this painting, reproduced with permission).

Giant Planet Core Formation

In the core accretion model, two-body mergers of rocky and/or icy planetesimals form the cores of future gas giants. To accrete their gaseous envelopes, these cores must reach a critical mass fairly quickly, before the gas nebula dissipates (a few million years).

Using the LIPAD (Levison et al. 2012) integrator, I run simulations that form planet-sized objects from a cold disk of planetesimals. I work with Martin Duncan (Queen's) and Hal Levison (SwRI) to investigate the key dynamical processes to lead to critical mass cores.

Our most recent results were presented at the IAUS 299 meeting and summarized in these proceedings.


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