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Research at St Andrews

Keith Douglas Horne


Keith Douglas Horne
Postal address:
School of Physics & Astronomy
Physical Science Building
North Haugh
St Andrews
United Kingdom


Web address:

Direct phone: +44 (0)1334 463322

Research overview

I have wide-ranging interests in many areas of astrophysics ranging from extrasolar planets to black hole accretion in galaxies to alternative gravity theories. My main expertise is in the interpretation of astrophysical observations, in particular developing novel data analysis and astro-tomography methods that extend the reach and resolution of observational data.

In the 1980's I worked mainly on accretion in compact binary systems, developing eclipse mapping and doppler tomography methods to make micro-arcsecond maps of the temperature profiles and emission-line distributions on the faces of the accretion disks in cataclysmic variables. For this I developed the optimal extraction algorithm for CCD spectroscopy, and maximum entropy reconstruction methods to convert the observed eclipse lightcurves and orbital phase variations of the emission-line profiles into accretion disk maps. (I developed similar methods to map x-ray coronae of rotating stars, and to make albedo maps of Pluto and Charon from mutual event lightcurves.)

In the 1990's I worked also on echo mapping of accretion flows into the supermassive black holes of active galactic nuclei, using light travel time delays to resolve structures 1-100 light days from the black hole, including the accretion disk and the broad emission-line regions. I adapted the maximum entropy methods to recover delay dsitributions and 2-dimensional velocity-delay maps of various emission-line regions, revealing their stratified ionisation structure and some aspects of the gas kinematics (virial flows) from which black hole masses and accretion rates are be measured.

I worked on science teams developing concepts and proposals for two space missions - NASA/Kronos and ESA/Eddington, neither of which was selected for flight.

In the 2000's I began work on detection of extrasolar planets by two methods. For hot planets, small wide-angle ground-based surveys (WASP, QES) have detected over 100 hot Jupiters transiting their host stars.  For cool planets, monitoring the lightcurves of microlensing events (PLANET, RoboNet) to detect occasional brief lightcurve anomalies that reveal the mass and orbit size of planets outside the snow line and down to just below the Earth mass. I recently proposed to repurpose the disabled Kepler satellite to measure microlens parallaxes, pending NASA approval to start in 2014.

I currently work mainly on two key projects exploiting our new network of nine 1m robotic telescopes (LCOGT/SUPA). The first monitors lightcurves of Galactic Bulge microlensing events to detect and characterise cool planets, and to characterise the mass and orbit size distribution of cool exoplanets outside the snow line and down to the mass of the Earth. The second monitors lightcurves of quasars, interpreting variations in terms of time-delayed reprocessing to measure quasar accretion disk T(R) profiles, black hole masses, accretion rates, and luminosity distances. My goal is to secure useful luminosity distances for reverberating quasar accretion disks out to redshift 3, to check and extend cosmological constraints from supernovae.

On a more speculative front, I am working to understand and develop astrophysical tests of Conformal Gravity, and to study Dirac solitons - localised quantum systems bound by their own self gravity - in both General Relativity and Conformal Gravity. My goals are to discover a simple alternative explanation for Dark Matter and Dark Energy phenomena, and to model elementary particles with fewer input parameters than the Standard Model.

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