Deciphering the atmospheric properties of hot gas giant exoplanets via ground-based transmission spectroscopy

Transiting hot gas giant exoplanets are great targets for atmospheric investigations due to their extended atmospheres and their strong obscuring effect on the observed starlight when they pass in front of their host star. Transmission spectroscopy can probe transiting exoplanets at various wavelengths and, hence, reveal the dominant opacity sources in specific regions of their atmospheres. In this thesis, I present groundbased transmission spectroscopy obtained in the optical for three exoplanets and describe the various analysis methods explored in order to produce the characteristic transmission spectrum for each exoplanet. The first target was the test case WASP-75b for which a rudimentary data reduction and analysis procedure resulted in a transmission spectrum of a low precision. The data set for this target was mainly used for practice purposes and so the analysis is brief. The next target was the low-density hot Saturn WASP-88b. Here, I examined a polynomial detrending approach and a detrending approach based on Gaussian Processes (GPs) in an effort to isolate the systematic effects from the transit light curves. The resulting transmission spectrum was found to be featureless with atmospheric models indicating the presence of high-altitude haze. The final target was the hot Jupiter WASP-74b. In this case, a new method that performs a common-mode correction only to the light curves of the target and considers an exponential of airmass during GP detrending was also presented in the spectroscopic analysis. This method resulted in increased transit depth precision and a steep scattering slope in the measured blue-optical transmission spectrum that suggests enhanced haze in the upper atmosphere. The results for WASP-88b and WASP-74b are representative of an emerging trend of steep scattering slopes observed in an increasing number of exoplanet atmospheres. The physics behind this spectral shape is not yet well-understood but several mechanisms have been proposed

Transmission spectroscopy with VLT FORS2 : a featureless spectrum for the low-density transiting exoplanet WASP-88b

PS was supported by a UK Science and Technology Facilities Council (STFC) studentship. CH acknowledges funding from the European Union H2020-MSCA-ITN2019 under grant agreement no. 860470 (CHAMELEON). NM acknowledges funding from the UKRI Future Leaders Scheme (MR/T040866/1), Science and Technology Facilities Council Consolidated Grant (ST/R000395/1), and Leverhulme Trust research project grant (RPG-2020-82).We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range of 4413−8333  Å with the FOcal Reducer Spectrograph (FORS2) on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise that we model using a Gaussian process and remove as a wavelength-independent component from the spectroscopic light curves. We analyse complementary photometric observations from the Transiting Exoplanet Survey Satellite and refine the system properties and ephemeris. We find a featureless transmission spectrum with increased absorption towards shorter wavelengths. We perform an atmospheric retrieval analysis with the aura code, finding tentative evidence for haze in the upper atmospheric layers and a lower likelihood for a dense cloud deck. While our retrieval analysis results point towards clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario.Publisher PDFPeer reviewe

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters arising from a Five Day Xallarap Effect in a Candidate Planetary Microlensing Event

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves $\chi^2$ values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters like mass-ratio, $q$, and separation, $s$, cannot be constrained well. However, we also find that the parameters for the source system like the orbital period and semi major axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of $P\sim5$ days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters.Comment: 19 pages, 7 figures, 6 tables. Accepted by A

Query Rewriting for Incremental Continuous Query Evaluation in HIFUN

HIFUN is a high-level query language for expressing analytic queries of big datasets, offering a clear separation between the conceptual layer, where analytic queries are defined independently of the nature and location of data, and the physical layer, where queries are evaluated. In this paper, we present a methodology based on the HIFUN language, and the corresponding algorithms for the incremental evaluation of continuous queries. In essence, our approach is able to process the most recent data batch by exploiting already computed information, without requiring the evaluation of the query over the complete dataset. We present the generic algorithm which we translated to both SQL and MapReduce using SPARK; it implements various query rewriting methods. We demonstrate the effectiveness of our approach in temrs of query answering efficiency. Finally, we show that by exploiting the formal query rewriting methods of HIFUN, we can further reduce the computational cost, adding another layer of query optimization to our implementation

Transmission spectroscopy with VLT FORS2: a featureless spectrum for the low-density transiting exoplanet WASP-88b

ABSTRACT We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range of 4413−8333  Å with the FOcal Reducer Spectrograph (FORS2) on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise that we model using a Gaussian process and remove as a wavelength-independent component from the spectroscopic light curves. We analyse complementary photometric observations from the Transiting Exoplanet Survey Satellite and refine the system properties and ephemeris. We find a featureless transmission spectrum with increased absorption towards shorter wavelengths. We perform an atmospheric retrieval analysis with the aura code, finding tentative evidence for haze in the upper atmospheric layers and a lower likelihood for a dense cloud deck. While our retrieval analysis results point towards clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters Arising from a Five-day Xallarap Effect in a Candidate Planetary Microlensing Event

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ ^2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q , and separation, s , cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ∼ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters