Searching for Young Exoplanets with High Contrast Imaging in an Effort to Constrain Models of Planet Formation

Abstract

Planets are expected to form by accreting material from a protoplanetary disc, with gas giant planets forming at large orbital radii where the gas is sufficiently cool. However, questions still remain regarding the dominant formation model of typical giant planets. These questions can be addressed by observing planets in the process of formation. Due to the wide separations, this is best observed through direct imaging but this presents many challenges. In this project, I bring theory and observations together to determine how likely we are to detect accreting planets and how we might constrain formation models.

I analysed data taken with the near infrared camera (NIRC2) on Keck-II in 2015-16 of the Taurus Molecular Cloud (TMC). This region is one of the closest star-forming regions to Earth and is a prime target for exoplanet searches. Although my analysis didn't detect any new substellar companions, I was able to place improved limits on NIRC2's sensitivity and place an upper limit on the frequency of giant planets in the TMC. I found that no more than 20% of stars in the TMC host a planet greater than 2MJ at separations beyond 70AU for a given assumption of planet occurrence rates.

In a more theoretical project, I investigated the current models of giant planet formation by core accretion to determine the expected brightness of accreting and young planets. Combining this with a suitable distribution of exoplanets and instrumental detection limits, I found that current instruments are insufficient to detect accreting planets, but future interferometers show great promise.

I also investigated the possible future detection and characterisation of exoplanets in nearby young moving groups combining direct imaging with Gaia astrometry. Using a model for planet magnitude as a function of initial entropy and mass, I investigated how well the initial entropy can be constrained by current and future instruments. I determined that the E-ELT and future interferometry with VLTI should be able to distinguish between different formation models. Show more