Honours Projects 2010

 




Ultra-High Signal-to-Noise Ration Spectra of Planet Host Stars

Honours Project Supervisor: Professor Chris Tinney


The Anglo-Australian Planet Search has been observing a sample of more than 200 stars for the last 10 years in a search for exoplanet hosts, in the process discovering almost 40 new exoplanets. Most stars have been observed at between 20 and 200 epochs over this time, and all have been observed at high S/N ratio. The stars are observed using an gaseous iodine absorption cell as a zero-velocity reference. This system works incredibly well, but it means that all AAPS spectra are imprinted with the molecular I2 absorption signature. In this project you will be deriving a procedure for fitting for this I2 absorption and removing it from each individual

spectra.


The resulting de-iodine spectra will be combined to produce some of the highest S/N ratio spectra for Sun-like stars ever produced, making a slew of new measurements of their elemental abundances possible. This database of spectra would be suitable for further processing for all sorts of projects (looking at line variability in the stars, abundances for elements with only weak lines that can't be seen in a single spectrum, looking at refractory element abundances in detail as per e.g. http://iopscience.iop.org/1538-4357/704/1/L66/fulltext).



J-band variability in T-type brown dwarfs
Honours Project Supervisor:
Professor Chris Tinney


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.


Over the last 4-6 years, a set of around 40 T-type and L-type dwarfs have been monitored at the AAT in an effort measure trigonometric parallaxes (ie. observe the small motions of these nearby stars, relative to background stars, as the Earth orbits the Sun).


This project is now near completion - a by-product of all these observations is a great deal of relative photometric information on these T- and L-type dwarfs. It would be interesting to either determine that these objects have no photometric variability in these pass-bands, or find that they are variable.


In this project you will be taking processed images for all these objects, measuring the amount of light coming from them relative to a set of reference stars, and determining the limits that can be placed on the variability of these objects. 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).


Parallaxes for L-type Brown Dwarfs
Honours Project Supervisor: Professor Chris Tinney


I have in hand about 4 years worth of data acquired at the AAT with the WFI camera of a sample of nearby L-dwarfs selected from the 2MASS all-sky survey. These data will be processed and subject to an astrometric analysis that should lead to the measurement of trigonometric distances to a large subset of the objects observed. In addition the same data will be used to provide improved photometric flux measurements for these brown dwarfs in the Gunn i and z passbands.