Activity in Exoplanet Host Stars
Honours Project Supervisor: Professor Chris Tinney

Extra-solar planets (ie. planet orbiting stars other than the Sun) are being discovered at a great rate of knots - over 250 are know known and they have all been detected in the period between 1995 and now. The vast majority have been discovered by the "Doppler Wobble" technique, which reveals exoplanet by the "reflex" Doppler motion they induce on their host star. However, Doppler Wobble observations are phenomenally challenging - to detect a Jupiter-mass planet in a Jupiter-like orbit requires monitoring a star at meter-per-second velocity precisions over periods of more than 12 years. Because even the highest resolution spectrographs deliver only kilometre-per-second velocity resolutions, this means our observations must operate at tiny fractions (~ several thousandths) of our instrumental precision, requiring superb control of measurement uncertainties.

Amazingly, these precisions are being achieved by programs like the Anglo-Australian Planet Search, and a major limiting factor is now the intrinsic stability of the host stars themselves, rather than our velocity measurements. On key limiting factor is the velocity variability induced by "stellar activity" - the sort of activity that produces flares and coronal outbursts in our Sun. We try to control this by observing only stars known to be stable, but even so it would be helpful to have a 'night-by-night' measure of activity in our target stars. Unfortunately, the most useful measure (the emission reversal in the core of the resonant Ca H and K lines near 390nm is not collected by our spectrograph when we do precision Doppler velocity observations.

However, it has recently been suggested that lines of He I that we do record, may also be useful. In this project you will be analysing spectra from our 9 years of Anglo-Australian Planet Search data to make estimates of the He I line reversals, and seeing whether they correlate with the known Ca HK activity of our target stars - if they do, we'll know that these lines can be extracted from all our planet search spectra to obtain estimates of the changes in activity levels of all our planet search stars, leading to improved precision and hopefully to new planet detections.

Brown dwarfs are the "little stars that couldn't" - they are objects formed in the same way that stars form, but which are too low in mass (ie. less massive than 0.075 solar masses) to burn nuclear fuel. As a result they radiate gravitational energy and cool throughout their lifetimes reaching temperatures as cold as several hundred Kelvin. Predicted to exist since the mid-60's, brown dwarfs were only detected in 1995, and have been an active area of astronomical research over the last 10 years.

Brown dwarfs share many properties with extra-solar planets - they have been found to have a mass range overlapping with that of the "exoplanets" detected orbiting nearby stars, and they can have similar temperatures. However, unlike exoplanets we can detect light form brown dwarfs, and as a result, they are an important way to gain insights into exoplanet properties.

Searching for Weather in Methane-rich Brown Dwarfs
Honours Project Supervisor: Professor Chris Tinney

In this project, AAT data taken in a set of methane filters (ie images taken with filters that sit both on, and off, strong methane features in the near infrared spectra of brown dwarfs) will be analysed to look for the signature of variable methane absorption. Brown dwarfs are know to rotate quite rapidly (with periods of a few hours up to tens of hours), so the detection of variable methane absorption on the surfaces of brown dwarfs will provide insights into whether brown dwarfs have banded or structured surfaces, or whether they are featureless.

For a look at some similar experiments on hotter brown dwarfs, you can read Tinney & Tolley, Monthly Notices of the Royal Astronomical Society, 304, 119, (1999), and Clarke, Tinney & Covey, MNRAS, 332, 361 (2002).