I am a Research Fellow based at Warwick University working with Dr. Heather Cegla using transiting planets to probe and (spectroscopically) resolve stellar surfaces. I studied for my Ph.D. at Armagh Observatory and Planetarium and Northumbria University where my thesis title was ‘Solar and Stellar Flares and Their Connection’. My main research interests lie in stellar variability, such as flares and starspots, and the impact they can have on orbiting exoplanet atmospheres and exoplanet detection. I kick-started my academic career in solar flare research investigating Doppler velocities through spectral analysis in plasma flows from Hinode/EIS and SDO/EVE. As a result of this, I remain active in the solar physics community using my knowledge to bridge the gap between solar and stellar research.
The search for life on other planets has become a prominent area of research in recent years. Missions such as Kepler and TESS, have discovered thousands of exoplanets by observing the change in brightness of stars as a planet crosses the stellar disk. Furthermore, transit photometric lightcurves combined with RV measurements provide details on planetary masses, composition and the overall nature of systems. However, inhomogeneties (such as granulation, plage/faculae and spots) on the surfaces of Sun-like stars induce velocity signals which can swamp the signal from a rocky, temperate planet.
When a planet transits a host star, a portion of the starlight is blocked from the line of sight and a distortion of the velocities is observed, known as the Rossiter-McLaughlin (RM) effect. The reloaded-RM (RRM) technique, isolates the blocked starlight behind the planet to spatially resolve the stellar spectrum. This starlight can be used to detect and characterise both stellar differential rotation (DR) and centre-to-limb convection-induced variations (CLV), and to determine star-planet obliquities. Stellar surface phenomena, such as DR and CLV, alters the observed stellar line profiles and can induce Doppler shifts which can mask/mimic the effects of planetary companions.
Stellar surfaces are covered in granules, bubbles of hot plasma which rise to the surface, cooling and falling back into
intergranular lanes. The net convective velocity shift caused by these granules changes as a function of limb angle (i.e. from the centre to the limb of the star) due to line-of-sight changes. Overall, these velocity shifts can impact the RM effect which is used to determine the projected obliquity. Therefore, ignoring the velocity contributions caused by granulation can bias or skew these measurements and impact our understanding of planet formation and evolution. Furthermore, DR plays a critical role in dynamo processes which are largely responsible for the generation of magnetic fields. Therefore, understanding DR and CLV are not just important for exoplanet characterisation, but for magnetic activity as a whole. Additionally, determining the projected 2D and true 3D obliquities of systems is of particular importance when considering planet formation, migration, and evolution.
Solar flares represent sudden increases in radiation which result from a rapid reconfiguration of the coronal magnetic field. Overall, these events are extremely powerful and are observed across the entire electromagnetic spectrum, possessing energy outputs up to 1032 erg. Magnetic energy released from solar flares can be observed as multiple phenomena including flare ribbons and post-flare arcades, but also in filament eruptions, coronal mass ejections (CME's) and blow-out jets. Overall, the pre-flare magnetic topology is responsible for deciding which of these phenomena will manifest to produce a solar flare.
Image Credit: NASA
Recently I have been working on ground-and-space-based solar observations from the Swedish Solar Telescope and Solar Dynamics Observatory of a solar flare event associated with a filament eruption and jet, which has been compared to a 3D MHD simulation (Doyle et al. 2019b). These observations provide the evidence to validate the simulation which can be applied to not only jets and CMEs but also confined eruptions and flares. Overall, the magnetic configuration observed in the event and in the simulation can be applied to multiple eruptive phenomena on the Sun. In turn, this can then be applied to stellar scenarios, scaling up the simulation to replicate flare energies observed in other stars. By monitoring the effects this has on the size and strength of sunspots we can determine whether it is likely these flares are generated through a similar magnetic field configuration or if it is more complex. Through this process, it is difficult to replicate the higher energies with realistic magnetic field strengths and spot sizes.
In addition to solar flares, stellar flares from both low-mass and solar-type stars have been observed over many decades with energies greatly exceeding 1033 erg. Known as ‘superflares’ these large outbursts can have severe consequences for any orbiting planet’s atmosphere, therefore, understanding their frequency and origin is vital for the existence of life.
Image Credit: NASA & L. Doyle
The brightness of many stars show periodic changes as the star rotates (see image above). This is widely thought to be the result of a dominant, large starspot/active region which is cooler than its surroundings and rotating in and out of view. From observations of the Sun, we know flares typically originate near sunspots, so it is natural to expect flares to originate from starspots in other stars. If the analogy between solar and stellar flares holds, then we would expect to see a correlation between the timing of stellar flares and flare number. I led two studies (Doyle et al. 2018, 2019) using one and two-minute photometric data from K2 and TESS to investigate the timing of flares in samples of 34 and 149 M dwarfs respectively. Utilising a simple statistical test, we investigated whether the distribution of the flares was random and concluded none of the stars in the sample show any preference for certain phase distributions. This is a big surprise, as it implies other stars do not behave like the Sun!
A full list of my publications can be found on Google Scholar here.
REFEREED (First author)
Doyle L., Ramsay G., Doyle J. G., (2020), Superflares and Stellar Variability on Solar-Type Stars Using TESS, MNRAS, 494(3), 3596-3610, doi:10.1093/mnras/staa923
Doyle L., Wyper P., Scullion E., et al., (2019b), Observations and 3D MHD Modeling of a Confined Helical Jet Launched by a Filament Eruption, ApJ, 887(2), 256, doi:10.3847/1538-4357/ab5d39
Doyle L., Ramsay G., Doyle J. G., Wu K., (2019a), Probing the Origin of Stellar Flares on M dwarfs Using TESS Sectors 1 - 3, MNRAS 489, 437-445, doi:10.1093/mnras/stz2205
Doyle L., Ramsay G., Doyle J. G., Wu K., Scullion E., (2018), Investigating the Rotational Phase of Stellar Flares on M dwarfs using K2 Short Cadence Data, MNRAS, 480, 2153-2164, doi:10.1093/mnras/sty1963
Ramsay G., Doyle J.G., Doyle L., (2020), TESS observations of southern ultrafast rotating low-mass stars, MNRAS, 497 (2), 2320-2326, doi:10.1093/mnras/staa2021
Doyle L., (2019), Exploring Flaring Behaviour on Low Mass, Solar-type Stars and the Sun, IAU Symposium 354, Copiapo, Chile, Proceedings of the International Astronomical Union, 15(S354), 384-391. doi:10.1017/S1743921319009980
Doyle L., Ramsay G., Doyle J. G., (2018), Searching for the Origin of Flares in M dwarfs, The 20th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Boston, USA, arXiv:1811.06594
Talks and Posters
A list of talks and posters which I have given recently, a full list can be found in my CV here.
April 2021 UKEXOM, Birmingham UK
July 2020 UKSP Discussion Days (Invited), UK
May 2020 AOP Online Seminar, Armagh, UK
Nov 2019 Invited Talk at Northumbria University, Newcastle, UK
Jul 2019 IAU Symposium 354: Solar and Stellar Magnetic Fields, Copiapo, Chile
Mar 2019 The Kepler & K2 Science Conference V, Los Angeles, USA
Jul 2018 The 20th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Boston, USA
Sep 2019 The Irish National Astronomy Meeting (INAM), Armagh, Northern Ireland, UK
Jul 2018 The 20th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Boston, USA
One of my main reasons for pursuing an academic research career is my passion for astronomy which I have held since I was a young girl! During both my undergraduate and postgraduate studies I was a key member of the outreach programmes in Glasgow and in Armagh.
During my academic career, I have organised, carried out, and assisted in a wide range of activities. This has included taking planetarium shows to local schools and events, public talks, and workshops. One of the biggest successes was the 'Hand on Science' Workshop at the Armagh Observatory and Planetarium which runs during school holidays for the public. I organised and put together 6 different workshops including three demonstrations ranging from comet making to gravitational waves and The Sun. Additionally, I ran workshops at the local Armagh Museum which brought together groups of children aged 8-12 from local schools, which involved talks and discussions along with practical activities to take the children on an adventure around the universe.
I have been an active member of Armagh's Project Juno Committee since its beginning in early 2017. This project is an initiative run by the Institute of Physics to promote gender equality in Physics institutions across the UK and Ireland. As a member, I have been involved in various activities including 'Women in Science' talks to local schools and Career events tailored to encourage young females to pursue STEMNET careers. This is something which I aim to continue within my new position at Warwick.