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Observations of exoplanetary systems at x-ray wavelengths
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King, George W. (2019) Observations of exoplanetary systems at x-ray wavelengths. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3490502~S15
Abstract
For planets with very small semi-major axes, the implications of residing so close to a star can be wide ranging. One of the most pertinent is the effect of the X-ray and extreme ultraviolet stellar emission, which can drive significant escape of material from close-in planets' upper atmospheres. For some smaller planets, the escape processes are sufficient to substantially evolve, and in some cases completely remove, any H/He envelope they were born with.
In my first study, I derive new empirical relations in order to perform the necessary extrapolation of the X-ray emission to the unobservable EUV energy band. In addition to inferring the properties of the XUV environment of the six planets in the sample and estimating their current mass loss rates, I make the first successful detection of a planet transit with the Optical Monitor on XMM-Newton for the hot Jupiter WASP-80b. The resulting near ultraviolet transit depth shows a hint of being shallower than is seen at visible wavelengths.
The photoevaporation valley is one of the observed effects of escape processes on the exoplanet population. I consider planets from two nearby systems that lie either side of this valley to investigate how XUV irradiation has affected each, both now and in the past.
I investigate planets from the young open cluster Praesepe, where significant XUV irradiation is still ongoing. All of the planets in that study lie close to either the photoevaporation valley, or the other main population feature caused by photoevaporation: the Neptunian desert. I assess their past, present and possible future atmospheric evolution.
The final two studies concern the same system. HD189733 hosts the closest transiting hot Jupiter to Earth. Using one of the largest collections of XMM-Newton observations for any late-type star, I make the first unambiguous detection of a planet transit at X-ray wavelengths. The deep transit reveals a large region of escaping planetary material leading the planet in its orbit. Finally, I investigate stellar activity from the system, predominately in the context of past claims of starplanet interactions. I identify new ares in the system, including some emanating from the previously-assumed-quiet wide stellar companion, and observe long-term variation possibly associated with a Solar-like activity cycle. However, I find no evidence of enhanced X-ray activity phased with the planet's orbit, and that evidence for the spinning up of star A by the planet is much weaker than previously claimed.
| Item Type: | Thesis or Dissertation (PhD) | ||||
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| Subjects: | Q Science > QB Astronomy Q Science > QC Physics |
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| Library of Congress Subject Headings (LCSH): | Extrasolar planets, Extrasolar planets -- Atmopsheres, Ultraviolet stars, Stars -- Atmospheres, Irradiation, X-ray astronomy | ||||
| Official Date: | October 2019 | ||||
| Dates: |
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| Institution: | University of Warwick | ||||
| Theses Department: | Department of Physics | ||||
| Thesis Type: | PhD | ||||
| Publication Status: | Unpublished | ||||
| Supervisor(s)/Advisor: | Wheatley, Peter J. | ||||
| Format of File: | |||||
| Extent: | xiv, 230 leaves : illustrations, charts | ||||
| Language: | eng |
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