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Trinity College Dublin, The University of Dublin

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Research Interests

Astronomical research has been carried out at TCD since the 1700's, and from 1792 until 1921, the Andrews Professor of Astronomy at Trinity was also Royal Astronomer of Ireland. Nowadays we carry out research on an extensive range of areas, including symbiotic stars, solar physics, space weather, active galactic nuclei, emission line diagnostics, and image processing and machine learning for astrophysics.

Some of our current projects are listed below:

Active Region Magnetic Fields

Solar flares and Coronal Mass Ejections (CMEs) are known to originate in the upper atmosphere of the Sun. At present there are no widely-available direct methods of detecting the magnetic field structure in the upper atmosphere of the Sun. Using measurements taken at the photosphere, we are developing methods of extrapolation the magnetic field from the surface. This will enable us to examine the changing topology of active regions as they emerge, flare and decay. Of particular interest is the location of magnetic null points and speratrix surface where magnetic reconnection is know to occur.

We are also developing multifractal techniques to characerise the changing complexity of surface magnetic field distributions in active regions. These methods are desribed in greater detail in Conlon et al (Sol. Phys., 2007). Further details on research in this area can be found on the Solar Physics Group website.

Symbiotic Novae

A nova is a thermonuclear explosion that occurs on the surface of a white dwarf star in a double-star system. It is thought that the dwarf star periodically accretes sufficient material from the outer layers of its companion for nuclear fusion to occur. The resulting thermonuclear detonation releases enormous quantities of energy and ejects large amounts of material outwards in an expanding shell. One subgroup of these objects are symbiotic binary stars (red giant + white dwarf) which undergo periodic outbursts. To understand the exact nature of these events, we are analysing a series of far-ultraviolet FUSE spectra. By analysing the absorption features diagnosing this material, we can learn about the composition and the thermal and dynamical properties of this gas.

Coronal Mass Ejections

Coronal Mass Ejections (CMEs) are large eruptions of plasma and magnetic field from the Sun which expand out into the solar system at hundreds of kilometers a second. They can impact the Earth's magnetic field, causing disruptions to satellite systems, GPS and telecommunication networks. The diffuse nature of CMEs observed by SOHO/LASCO and STEREO make it difficult to identify their morphology and kinematics. We are therefore developing multiscale image processing techniques to study the detailed physics of CMEs. By automatically determining the CME front, its kinematics can be studied (height, velocity, acceleration) as well as its morphology (curvature, expansion, rotation).

Stellar Winds from Red Giants and Supergiants

Red giants are observed to drive matter back into space in outflows called stellar winds. For many types of stars there are theories that can explain this phenomenon, but for the red giant and supergiant stars there is no working theory. Our understanding is being driven by detailed new observations across the electromagnetic spectrum. At Trinity College we are combining measurements of the outflow velocities (which inform us about the momentum balance) with new techniques to measure the outflow temperature (which inform us about the energy balance). These are being used to confront theoretical models.

Winds of cool stars and exoplanets

As the stellar wind outflows, its permeates the interplanetary medium, interacting with any exoplanet encountered on its way. The interaction between exoplanets and their host star's wind can give rise to observable signatures, such as exoplanetary radio emission and enhancement of stellar activity, providing invaluable Physical insight into the system. This interaction can also cause erosion of the planet's atmosphere, removing an important shield for creation and development of life. Here, at Trinity College, we investigate these interactions by means of data-driven 3D numerical simulations of winds of cool stars. The realistic account of the stellar wind can therefore supply more detailed diagnostics of its interaction with exoplanets, guiding observers towards the most promising exoplanetary systems to host detectable signatures of such interactions.

Magnetic fields of low-mass stars

Studies of solar magnetism have provided us with fantastic spatial (i.e., enabling us to resolve small-scale structure of the solar magnetic fields) and temporal (with cadences reaching less than a minute) resolutions. Studying magnetism in stars, although observationally challenging, is equally rewarding. In particular, observations of low-mass stars, despite being less detailed, allow us to put the Sun in a much more general context. Past studies have demonstrated that cool dwarf stars harbour at their surfaces large-scale magnetic fields with a wide variety of intensities and topologies. Here, at Trinity College, we aim to interpret stellar magnetism data in the wider context of stellar magnetic field theory. The results of this can be used to guide studies of stellar winds, which will then have key applications on our understanding of rotational evolution and stellar wind effects on exoplanets.

This research is supported by Science Foundation Ireland, IRCSET, the EU's Framework Programmes, the Royal Irish Academy, ESA and NASA.