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Detection of stellar flares and a transiting brown dwarf with the next generation transit survey
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Jackman, James A. G. (2020) Detection of stellar flares and a transiting brown dwarf with the next generation transit survey. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3491634~S15
Abstract
Stellar flares are explosive phenomena caused by reconnection events in the magnetic fields of stars. They emit across a wide range of wavelengths but notably in the optical, UV and in X-rays. They are some of the highest energy events seen from other stars and they regularly dwarf those seen from the Sun. They are regularly seen on low mass stars and provide a way of studying the magnetic activity of these systems. Their role in exoplanet habitability (in particular for low mass stars) has become increasingly relevant in recent years, necessitating studies of their energies and occurrence rates.
In this thesis I present observations and analysis of stellar flares detected with the Next Generation Transit Survey (NGTS). These flares come from stars ranging from G to L spectral type. I also present the detection and analysis of the transiting brown dwarf NGTS-7Ab, discovered in part because of the multiple flares detected from the M dwarf host star.
These flare detections include the first ground-based CCD detections of superflares from a G-type star, NGTS J030834.9-211322. I used the high cadence NGTS observations to apply a Solar inspired empirical flare model, one which does not require arbitrary break points between the flare rise and decay.
I also present the detection of a giant flare from a pre-main sequence M star. This flare was one of the most energetic detected from an M star and displayed quasi-periodic pulsations in the flare peak. I apply solar techniques to analyse these oscillations and identify their cause.
I present the first detection of a white-light flare from an L2.5 dwarf. This is the coolest star to ever show a white-light flare to date and shows strong tranxiii sient magnetic activity can persist to the brown dwarf boundary. I also show how full frame images in wide-field exoplanet surveys, provided they are a high enough cadence, can be used to detect flares from the faintest and coolest stars.
I present the detection of NGTS-7Ab, an ultra-short period brown dwarf around a tidally locked and active M star. I analyse the entire system, showing through a kinematic and photometric analysis that it is likely a hierarchical triple system formed of two active M stars (NGTS-7A and NGTS-7B) and a transiting brown dwarf (NGTS-7Ab). This is the shortest period transiting brown dwarf discovered to date and it has spun up and tidally locked its host star, placing the system in a state of spin-orbit synchronisation.
Finally, I discuss the detection of white-light flares from pre-main sequence stars associated with the Orion complex. These stars have an average age of 4 Myr. I measure the average flare occurrence rate for M0-M3 stars, finding a non-linear relationship between flare occurrence rate and cluster age.
My work shows how the ground-based NGTS observations can rival those available from space for high energy white-light flare events. Throughout this work I also discuss the possible effects flares may have on nearby exoplanets, along with how the detected flare events relate to other signs of magnetic activity such as starspots.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QB Astronomy | ||||
Library of Congress Subject Headings (LCSH): | Solar flares -- Observations | ||||
Official Date: | June 2020 | ||||
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: | xv, 245 pages : illustrations (chiefly colour) | ||||
Language: | eng |
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