Utilising Galactic Archaeology Surveys for Exoplanetary Science

Utilising Galactic Archaeology Surveys for Exoplanetary Science

During the last decade, a wealth of new large-scale surveys have come online across the world. These huge spectral, astrometric and photometric surveys are providing astronomers with the richest datasets to date, to better characterise stars contained within the Milky Way like never before. Not only are these resources used to better understand the formation and evolution of our Galaxy and the stars contained within it, but these surveys can also be used to better understand the exoplanets found within the Milky Way. More planets are now being discovered in our galaxy, thanks largely to NASA’s new exoplanetary mission, the Transiting Exoplanet Survey Satellite (TESS). TESS has been operating since 2018, with an unprecedented number of stars being observed to monitor transit signals of exoplanets around nearby stars.

My thesis firstly cross-matched spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the TESS Input Catalog and Gaia Data Release 2, to create a curated, self-consistent catalog of physical and chemical properties for 47,285 stars, known as the GALAH-TESS catalog. Using these data, this thesis has derived isochrone masses and radii that are precise to within 5%. These masses and radii have then helped redetermine the physical properties of known and candidate exoplanets, casting doubt on the exoplanetary nature of at least three candidate systems discovered by TESS.

The GALAH-TESS catalog contains abundances for up to 23 elements that specifically contains the abundance ratios for C/O, Mg/Si, Fe/Si and Fe/Mg, to assist in determining the composition and structure of planets with Rp < 4R⊕. From these ratios, 36 % fall within 2 sigma of the Sun/Earth values, suggesting that these stars may i host rocky exoplanets with geological compositions similar to planets found within our own Solar system.

With GALAH releasing DR3, to include the K2 fields and the Southern TESS continuous viewing zone, and Gaia releasing EDR3, my thesis then focused on improving the characteristics of known and candidate exoplanets and their host stars. This thesis not only revises the physical properties for hundreds of confirmed and candidate exoplanets, but it has also decreased the uncertainties for some of these derived properties too. It was able to improve the parameters for five ultra-short period exoplanets, in particular, refining the radius and mass of three to their most precise values yet, to less than 2.3% and 8.5% uncertainty respectively. The radius estimate for CoRoT-7 b further suggests that it is large enough for an atmosphere to contribute to its overall radius. It also uncovered that Ultra-Hot Neptunes are more likely to be found around thick-disc stars rather than their thin-disc counterparts.

Finally, my thesis presents the discovery of a hot-Jupiter orbiting a rapidly rotating (vsin (i) = 28 km s-1) early F dwarf HD 115447 (TOI-778). Combining the transit signal taken from Sector 10 of TESS’s initial detection of the exoplanet, this thesis also uses ground-based photometry, along with radial velocity measurements taken from Minerva-Australis, TRES, CORALIE and CHIRON to confirm and characterise TOI-778 b. A spectroscopic transit of TOI-778 b was taking to derive its spinorbit angle of 19.1±9.6 degrees, consistent with an aligned planetary system.

Jake T Clark, et al., The GALAH Survey: using galactic archaeology to refine our knowledge of TESS target stars, Monthly Notices of the Royal Astronomical Society, Volume 504, Issue 4, July 2021, Pages 4968–4989, https://doi.org/10.1093/mnras/stab1052 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

Jake T Clark, et al., The GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys, Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 2, February 2022, Pages 2041–2060, https://doi.org/10.1093/mnras/stab3498 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2022 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

Robert A Wittenmyer, et al., K2-HERMES II. Planet-candidate properties from K2 Campaigns 1-13, Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 1, July 2020, Pages 851–863, https://doi.org/10.1093/mnras/staa1528 (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.)

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