Research Interests

1. Extrasolar Planets and Stellar Variability

SMEI: Stellar Variability with the SMEI Instrument

The SMEI instrument (onboard the CORIOLIS satellite) monitors the brightnesses of bright stars over the entire sky. We are using SMEI to investigate stellar variability and search for transiting extrasolar planets. The SMEI data is long (5 years) and has very good coverage (almost continuous for some stars) meaning it is good at discovering pulsational frequencies in stars..

The image on the right shows the CORIOLIS satellite prior to launch. The 3 SMEI cameras are located near the base of the satellite. The dish at the top is associated with the WINDSAT instrument.

Several papers have now been published using data from the SMEI instrument. Examples include

with ongoing work on eclipsing binaries, CU Virginis (a magnetic cehemically peculiar star) and a survey of Beta Cepheid stars.

STEREO: The STRESS Survey using the STEREO HI instruments

STRESS: STEREO TRansiting Exoplanet and Stellar Survey

The STRESS survey is conducted using the Heliospheric Imager (HI) instruments on board the 2 STEREO satellites, to search for extrasolar planets (via the transit method) and also to study stellar variability. The HI instruments observe a region near the limb of the Sun and in doing so image a large number of stars. As the satellite orbits around the Sun we can monitor the brightness of many hundreds of thousands of stars.

The image on the left shows an artists impression of the 2 STEREO satellites in orbit around the Sun.

Some preliminary results from the STRESS survey can be found by following this link: STRESS Paper 1

KEPLER: Stellar Variability

I am involved in several different projects using data from the KEPLER satellite. Links to the papers are provided below:

2. Stellar Radio Emission from Exoplanets, Brown Dwarfs and Magnetized Stars

The Search for Magnetospheric radio emission from Extrasolar Planets and Related objects.

We expect massive extrasolar planets to be magnetized and to have substantial low-frequency radio emission. The mechanism responsible for the radio emission is called the Electron Cyclotron Maser (ECM). This is the same mechanism that gives rise to the emission from the Solar System planets (Jupiter in particular is a bright radio source). We are conducting searches for this emission from extrasolar planets.

The theory behind the radio emission for extrasolar planets can be found here: Paper and results from a search using the GMRT in India at a frequency of 150MHz can be found here: Paper

In addition to searching for extrasolar planets we are investigating the Electron Cyclotron Maser emission from more massive objects, such as brown dwarfs and magnetic chemically peculiar (MCP) stars. In both of these cases we expect stronger magnetic fields and emission extending up to higher frequencies.

Some results on these studies can be found at: Paper

3. Massive Stars and Young Star Clusters

The most massive (Wolf-Rayet and OB stars) stars are extremely energetic objects, that are losing mass at a prodigious rate via supersonic stellar winds. The wind terminal velocities can be several thousand km/s and the mass-loss rates can be up to around 1e-4 solar masses per year.

I work in a range of topics in this general area, mostly concerning massive stars that are in binary systems (and indeed most massive stars are in binary or triple systems) or very young stellar clusters, such as NGC3603 (and again most massive stars are formed in star clusters and are still in star clusters while they are O stars).

Colliding Stellar Winds

Most massive stars are found in binary system and when the fast wind collide the result is substantial X-ray emission. I have been involved in numerous studies of the X-ray from colliding winds using several different satellites (ROSAT, ASCA, Chandra, XMM-Newton).

The X-ray emission is very variable and yields important information about the properties of the wind and the radiation hydrodynamics of the wind (which are driven by the radiation pressure from the hot luminous stars).

For some recent results on the winds in the Eta Carina system (one of the most spectacular stars in our galaxy) see this link.

Massive Young Star Clusters

An ongoing project in this area is COBRaS. A full description of this project can be found here.

COBRaS involves observations of the Cygnus OB2 cluster, primarily with the E-Merlin array, but using appropriate data from a range of other satellites and observatories.

Cyg OB2 is a young (a few million years old) and massive cluster. The project will deliver the most detailed radio census for the most massive OB association in the northern hemisphere, offering direct comparison to not only massive clusters in general, but also young globular clusters and super star clusters in other galaxies. The sources detected will primarily be massive stars with strong stellar winds, but also a large number of young stellar objects (YSOs) will also be detected.

I have also used X-ray observations to study nearby star-clusters, focusing on the cluster wind - the combined wind from the entire cluster that results from the combination of the indnvidaul stellar winds. A review of this area (both observational and theoretical) can be found here. and a more detailed paper can be found here.

Starburst Galaxies

Topics covered:

X-ray observations of starburst galaxies.

Diffuse X-ray emission and populations of X-ray point sources.

X-ray and radio observations of ULX sources.

Modelling of superwinds

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