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Astrophysics Research Centre

School of Mathematics and Physics


I am currently running a number of projects, a few of the main ones are outlined below.

Understanding and reducing astrophysical noise - towards young planets and Earth-like alien worlds

Surface inhomogenities on stars (such as starspots, flares, plage and even granulation) can induce apparent radial velocity wobbles of the star to be observed. This is somewhat annoying, as the only way of really weighing (and, in fact, also confirming the presence of) an orbiting planet around another star is by measuring the radial velocity wobble it induces on its host star (the so-called Doppler wobble effect). At its worst, the systematics created by stellar surface inhomogenities (collectively termed astrophysical noise) can actually mimic orbiting exoplanets - at other times they induce radial velocity jitter that can mask the presence of planets.

By-and-large, astronomers circumvent astrophysical noise by searching for planets around old, inactive stars. Unfortunately, younger stars exhibit far higher levels of magnetic activity and hence searching for young planets (and thereby probing the evolution of planetary systems) is severely hampered by astrophysical noise, even for the most massive hot-Jupiters (which are the easiest to detect). We are therefore observationally ignorant of how planetary orbital radii, eccentricities and characteristics change as a function of time. And assuming that our theoretical understanding of how older exoplanets came to reside at their current locations is correct should be regarded as shaky. After all, it wasn't that long ago that the existence of hot-Jupiters was, well, theoretically rather unexpected….

Astrophysical noise produces yet another stumbling block when it comes down to the push to measuring the masses of terrestrial- (or Earth-) sized exoplanets. While instrumentation can now measure the reflex motion of a star pacing back-and-forth at the speed of 1 metre/second (we can measure something over 1,000,000 km wide moving at a gentle stroll tens of light years away!!), the Earth causes the Sun to wobble by less than ~10 cm/second. Planned instrumentation will undoubtedly achieve this precision, but even for the most quiet stars astrophysical noise is an issue at the sub-metre/second level. In other words, our ability to build advanced instrumentation is unlikely to determine whether we are able to detect, confirm and characterise Earth-sized alien worlds. Rather, it is our lack of understanding of astrophysical noise that sets our planet detection capabilities.

The exoplanet group at QUB has been working on methods to reduce astrophysical noise. Here are some Astrophysical Noise Reduction results for young systems. In addition, in collaboration with the QUB solar group, we are also modifying state-of-the-art magento-convection simulation of the Sun to understand, assess, and counter the radial-velocity jitter created by grannulation cells which will ultimately lead to enabling the efficient detection of radial velocity signatures of small, rocky planets orbiting in the habitable zones of solar and low-mass stars.

Mapping exoplanet atmospheres

In addition, I keep my fingers in a number of other pies as well. These include astrotomography and its applications to binary systems in order to advance our knowledge of stellar activity and accretion dynamics.

I also lend a hand with a few construction projects, such as the 1-m SAFT.

users/cawatson/research.txt · Last modified: 2013/10/08 11:19 by Robert Ryans

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