Sniffing the skies of new worlds

: characterising the atmospheres of extrasolar planets using ground-based secondary eclipse observations

Abstract

This thesis presents ground-based secondary eclipse observations of three ultra-hot Jupiters conducted at wavelengths that are not routinely observed by the Hubble or Spitzer space telescopes. Observations of exoplanets during their secondary eclipses — when they are occulted by their host stars — are important tools to classify the atmospheres of their daysides.

In the first study, I present a secondary eclipse observation of KELT-9b — the hottest known exoplanet — in the {/-band, a window particularly sensitive to reflected light from Rayleigh scattering. I did not detect a secondary eclipse signal, but my 3cr upper limit of 181 ppm on the eclipse depth allowed me to constrain the dayside temperature of KELT-9b at pressures of ~ 30mbar to < 4,995 K at 3o\ Although I could place an observational constraint on the geometric albedo of Ag < 0.14, models suggest that the actual value is considerably lower due to H~ opacity.

In the second study, I present two secondary eclipse observations of WASP-12b in the /'-band, a window expected to be dominated by TiO and VO features if present in appreciable quantities in the upper atmosphere. The two measured depths (0.97 ±0.14 and 0.44 ± 0.21 mmag) significantly disagree, mirroring similar observations that have previously been conducted for WASP-12b in the z'-band. I explore potential explanations for these disagreements, including variable thermal emission in the dayside of WASP-12b, a possibility I cannot rule out from my analysis.

Finally, I present three secondary eclipse observations of KELT-16b in the 7- and Ks- bands: windows where ultra-hot Jupiters emit very strongly. The measured eclipse depths were 2.47 ± 0.31 mmag in the 7-band, and 4.21 ± 0.39 and 2.33 ± 0.22 mmag in the Ks-band. The possibility of atmospheric variability is negated due to the fact that the A^-band observations occurred on consecutive nights. Together they indicate a very hot dayside for KELT-16b, along with a very low albedo and very poor dayside - nightside recirculation efficiency.

Date of Award	Dec 2019
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Christopher Watson (Supervisor)