Low resolution transmission spectroscopy of exoplanet atmospheres using ground-based and space telescopes

The research on exoplanet atmospheres has expanded rapidly over the last two decades since the first detection of an exoplanet atmosphere. Hot Jupiters– gas giants orbiting their host star on very close-in orbits–have always been at the forefront of exoplanet research as they are the easiest to detect due to their size and short orbits. However, their origins are not fully understood and by studying their atmospheres we aim to gain insight into their formation and evolution. In this thesis I present spectroscopic observations of three transiting hot Jupiters. For the first two exoplanets I am utilising data from the ground-based telescope NTT (La Silla Observatory), while for the last one data from the space telescope JWST is used. My study of the atmosphere of WASP-94Ab in the optical wavelength range revealed a sodium absorption as well as a scattering slope indicative of Rayleigh scattering. The optical transmission spectrum of HATS-46b I retrieved using ground- based data showed a fairly feature less spectrum and the atmospheric retrieval anal- ysis provided evidence for clouds in the atmosphere. The last observations presented in this thesis used JWST/NIRCam data of hotJupiter WASP-39b in the infrared wavelength range, and were part of the JWST Early Release Science(ERS) program from the Transiting Exoplanet Community. The retrieved spectrum showed strong watervapour absorption and indicated a low carbon-to-oxygen(C/O)ratio. I show that the two telescopes provide access to different wavelength ranges and thus different possible scientific findings. Combining data from different tele- scopes/instruments from both ground-based and space telescopes is becoming more important than ever for our field to help understand degeneracies in both models and data, in order to further our knowledge of exoplanet atmospheres and in turn learn about the origins of hot Jupiter

LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b

We have performed low-resolution ground-based spectroscopy of HATS-46 b in transmission, using the EFOSC2 instrument on the ESO New Technology Telescope (NTT). HATS-46 b is a highly-inflated exoplanet that is a prime target for transmission spectroscopy, having a Jupiter-like radius (0.95 R$_\textrm{Jup}$) but a much lower mass (0.16 M$_\textrm{Jup}$). It orbits a G-type star with a 4.7 d period, giving an equilibrium temperature of 1100 K. We observed one transit of HATS-46 b with the NTT, with the time-series spectra covering a wavelength range of 3900 - 9000 Angstrom at a resolution of $R \sim 380$. We achieved a remarkably precise transmission spectrum of 1.03 $\times$ photon noise, with a median uncertainty of $357$ ppm for $\sim 200$ Angstrom wide bins, despite the relative faintness of the host star with $V_{\mathrm{mag}} = 13.6$. The transmission spectrum does not show strong absorption features and retrievals favour a cloudy model, ruling out a clear atmosphere with $3.0\sigma$ confidence. We also place a conservative upper limit on the sodium abundance under the alternative scenario of a clear atmosphere. This is the eighth planet in the LRG-BEASTS survey, which uses 4m-class telescopes such as the NTT to obtain low-resolution transmission spectra of hot Jupiters with precisions of around one atmospheric scale height.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in MNRA

Identification of carbon dioxide in an exoplanet atmosphere

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called ‘metallicity’)1,2,3, and thus the formation processes of the primary atmospheres of hot gas giants4,5,6. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets7,8,9. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification10,11,12. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme13,14. The data used in this study span 3.0–5.5 micrometres in wavelength and show a prominent CO2 absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative–convective–thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models

LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2

Stars and planetary system

The HARPS search for southern extra-solar planets XLV. Two Neptune mass planets orbiting HD 13808: a study of stellar activity modelling's impact on planet detection

We present a comprehensive analysis of 10 years of HARPS radial velocities of the K2V dwarf star HD 13808, which has previously been reported to host two unconfirmed planet candidates. We use the state-of-the-art nested sampling algorithm PolyChord to compare a wide variety of stellar activity models, including simple models exploiting linear correlations between RVs and stellar activity indicators, harmonic models for the activity signals, and a more sophisticated Gaussian process regression model. We show that the use of overly-simplistic stellar activity models that are not well-motivated physically can lead to spurious `detections' of planetary signals that are almost certainly not real. We also reveal some difficulties inherent in parameter and model inference in cases where multiple planetary signals may be present. Our study thus underlines the importance both of exploring a variety of competing models and of understanding the limitations and precision settings of one's sampling algorithm. We also show that at least in the case of HD 13808, we always arrive at consistent conclusions about two particular signals present in the RV, regardless of the stellar activity model we adopt; these two signals correspond to the previously-reported though unconfirmed planet candidate signals. Given the robustness and precision with which we can characterize these two signals, we deem them secure planet detections. In particular, we find two planets orbiting HD 13808 at distances of 0.11, 0.26 AU with periods of 14.2, 53.8 d, and minimum masses of 11, 10 Earth masses

Evaluation of 3 rapid diagnostic tests (CareStart) Malaria 3 line pl.DH (Pan, Pf), OptiMAL-IT pl.DH (Pan, Pf) and CareStart 0 2 line.pl.DH (Pan) for the diagnosis of malaria in Myanmar

Presented at the conference of the American Society of Tropical Medicine and Hygiene 200