Atmospheric characterization of high-gravity hot Jupiters with ACCESS

Abstract

The previous month marked the 5,000th confirmed exoplanet discovery, a milestone in the next era of exoplanet science, exoplanet characterization. To that end, several recent ground and space-based surveys have begun detailed follow-up analysis of roughly 5% of this known population so far to search for potential trends in their atmospheric properties, but no clear correlations with observable planetary or stellar parameters have been borne out just yet. Lessons learned from the brown dwarf (BD) community and advances in theoretical cloud microphysics modeling indicate that surface gravity may play an important role in cloud and haze formation, motivated in part by the redder near-IR colors observed in young, directly imaged Jupiters compared to their BD counterparts, which is attributed to the persistence of titanium oxide and vanadium oxide clouds, and other aerosols, that persist above the photosphere of the lower gravity objects. Other recent studies indicate a tentative trend between surface gravity and the \SI{1.4}{\micron} water amplitude feature measured in transmission, although this is not a conclusive result. Unfortunately, we do not currently have the data available from a statistically significant population of hot Jupiters spanning a wide enough range in surface gravities to test these potential trends more thoroughly. To help address this, I present new optical-near IR ground-based transmission spectra observations and atmospheric analysis for three exoplanets. These planets were observed with the Inamori-Magellan Areal Camera and Spectrograph (IMACS), and in part by the Low Dispersion Survey Spectrograph (LDSS3C), aboard the 6.5-meter Magellan telescopes at the Las Campanas Observatory in Chile, as part of the Atmospheric Characterisation Collaboration for Exoplanet Spectroscopic Studies (ACCESS), an inter-institutional survey dedicated towards the production of homogeneous transmission spectrum measurements in the visible portion of the spectrum. The three exoplanets, known as high-gravity hot Jupiters (HGHJs), have surface gravities ($g \gtrsim \SI{20}{m/s^2}$), which tend to be larger than the majority of surface gravities of hot Jupiters with already measured transmission spectra. I found the first entry, WASP-43b, to have a primarily clear atmosphere with features attributed to a combination of unocculted heterogeneities present on the surface of the host star from and water in the planet's atmosphere consistent with previous IR results. In the second entry, HAT-P-23b, I made observations indicating a primarily clear atmosphere as well, with a tentative presence of TiO. For the last entry, WASP-50b, I was unable to distinguish between any one particular atmosphere type given the current level of precision. Together, all three targets provide crucial observations that did not exist until now in this wavelength range in the case of WASP-43b, or at all, in the case of the last two targets. Transmission spectra covering a wide wavelength range are necessary to place constraints on atmospheric retrievals of exoplanet atmospheres, and our observations in the optical-near IR made by ACCESS will complement future ground and space-based efforts made in the UV and IR portions of the spectrum, especially supplementing observations from the \textit{James Webb Space Telescope} (JWST) that will only be capable of making observations in the IR. A statistically significant sample of observations of this type of planet will be necessary to perform these characterizations on a comparative exoplanetology scale, so here I will also provide a list of potential HGHJs that would be amenable to follow-up study.