PhD Projects in Exoplanetary Science


PhD Projects with Professor Chris Tinney

Our research group focuses on exoplanetary detection using "Doppler Wobble" and direct imaging techniques. We also pursue studies of brown dwarfs - objects somewhat more massive and brighter than exoplanets, but which we can actually see - in order to gain insight into exoplanetary properties. These areas encompass a large range of possible projects - to give a flavour of the sort of work involved, a few of them are spelled out in more detail below. But this is by no means an exhaustive list.

Our focus in supervising PhDs is to train students for a subsequent career as an independent, astronomical researcher. So you'll be travelling to telescopes in Australia and overseas to do observing, analysing data, writing papers, and presenting results at international conferences - and we have funds to support you in doing all that.

We offer students a Top-up Scholarship of $6000 per annum, for students in our group who hold an existing scholarship (i.e. Australian or University Postgraduate Award or an international scholarship at an equivalent level).

There are two main requirements for becoming a UNSW graduate student,

  1. Being accepted in the Graduate Research School, and

  2. Accessing funding to support you while undertaking research full time for three years.

Australian students should see the Graduate Research School web pages for details on how to Apply for an Scholarship at UNSW (deadlines are around end of October for Semester 1, around end of March for Semester 2) and how to Apply for Admission (deadline around mid-December and late-May).

Prospective students from overseas (in addition to Applying for Admission - deadlines around mid-December and late-May) will have to pay tuition fees. Again there are Scholarships available (see UNSW International Research Scholarships for details - deadlines are a few months earlier than for Australian scholarships). These scholarships are very competitive.  You will need to have an undergraduate degree equivalent to at least First Class Honours level (in the Australian/UK system) - this is roughly equivalent to a GPA in the US system of better than ~3.6 (see this link for more details). It will also be essential to be able to obtain good references from researchers who know you and can recommend that you have the potential to be a research scientist.

Your home country may also have scholarships available to support overseas study.

UNSW requires applying students to have discussed possible projects and organised a prospective supervisor in advance of applying for admission or any of these awards. So, if the PhD experience outlined above sounds interesting to you, please contact me well in advance of these deadlines, so we can discuss possible projects.

Chris Tinney

February 2011

The Hunt for Free Floating Planets

Over 230 extra-solar planets are now known to orbit nearby stars. Most of these have been discovered by the Doppler wobble technique, and so have only been "indirectly" detected via their impact on their host star. So none of these planets has actually been seen directly. In this project you will use the recently developed technique of methane imaging to search for, and image, "unbound" planets (ie planets without a host star) and brown dwarfs (ie. stars too low in mass to burn nuclear fuel) in young southern star clusters.

Planets are believed to form in the accretion disk via which interstellar material is fed onto young forming stars. It is known that both planets and stars can be formed over a large range of masses, with the lowest mass objects formed like stars (brown dwarfs) having masses so small that they overlap with the masses of the largest planets. The aim of this research project will be to compare the number distribution of the objects in young star clusters with masses of 1-30 Jupiter masses, with the number distribution of more massive stars, in an effort to disentangle the multitude of possible formation mechanisms of stars and planets.

The primary tool for this will be methane imaging. The coolest objects detected to date outside our solar system are "T-dwarfs" - star-like objects with temperatures of 800-1300 Kelvin that show pronounced features in their near-infrared spectra due to methane absorption. Methane imaging (ie near-infrared imaging in bands at 1.5-1.65 and 1.6-1.75um) can powerfully discriminate these rare objects from all other contaminating objects in the fields of young star clusters. Moreover, when used to detect young objects, it can reveal objects as low in mass as 1 Jupiter mass.

Current Work: The observational tools for projects searching for methane T-dwarfs in star clusters are wide-field near-infrared imagers. The IRIS2 instrument on with the Anglo-Australian Telescope and the HAWK-I instrument on the VLT are currently being used by PhD students Stephen Parker and Shane Hengst to target the cluster IC2391 and the star forming region in Corona Australis. The Southern Hemisphere is the ideal location to undertake these studies, as it harbours many of the nearby Galactic star clusters. As a result there is lots of scope for additional students to join the current team working in this area.

Future Projects - FourStar: There exists substantial scope for more work targetting free-floating planets in star-forming regions. In 2010, the FourStar instrument will go into operation on one of the 6.5m Magellan telescopes in Chile. This instrument will have a massive field of view of 0.18x0.18 degrees, allowing it to targeting nearby (ie. within 150pc) and larger (ie. several square degrees on the sky) star clusters. The University of NSW, together with the Carnegie Institution and MIT, has funded the purchase of methane filters specifically for this new camera. FourStar will make possible large surveys of Southern clusters that have previously only been poorly studied at very low masses, like like IC2602, NGC2461, NGC2547, and NGC6475.

Future Projects - Gemini MCAO Imaging:
in 2010 the Australian-built Gemini South Adaptive Optics Imager (GSAOI) will go into operation on the 8m Gemini telescope in Chile, together with the Canopus Adaptive Optics system. Together these components will enable one of the largest telescopes in the world to deliver diffraction-limited high-resolution images over a wide field (1-2')  on a ground-based 8m telescope. This will enable entirely unprecedented observations of star more distant and denser star clusters.

Perhaps the most obvious and most immediate target will be the Orion Nebula Cluster (right). This region is home to a dense, massive star cluster, which HST images have show to not only harbour objects down at brown dwarf masses, but also to host back-illuminated accretion disks (or "proplyds" - see left).

Gemini NICI Imaging of AAPS Host Stars

Over the last 6-9 months, the Gemini Observatory has been commissioning its Near-Infrared Coronagraphic Imager (NICI).  This dual-channel imager represents the current state-of-the-art for the direct detection of faint young planets and brown dwarfs orbiting nearby stars.

Around 20% of the stars currently being monitored by the Anglo-Australian Planet Search (AAPS) team show radial velocity variations. In some cases these are so large that the unseen companion is obviously a brown dwarfs of low-mass star - which category it falls into will depend on the system's orbital inclination to our line of sight. NICI observations can clarify this status, as low-mass stars will be easily detectable, while brown dwarfs will be much fainter (though possibly still detectable). In either case, long-term monitoring will allow all orbital elements for these systems to be determined.

In other cases, the Doppler wobble we see is almost certainly due to a gas-giant planet - most of which will be undetectable by NICI. However, once again if NICI does see something in these systems it will be an exciting result. Either there are further, more distant, planets that Doppler observations have not yet detected. Or the system is much younger than we expected. Either case will be a significant result.

The AAPS team, therefore, will be applying for NICI time in 2010 to image all of our Doppler variable target stars, and there is a role for a PhD student to be involved in acquiring, reducing and analysing this data, as well as preparing for any further follow-up observations required.

Understanding Intrinsic Variability in Doppler Planet Host Stars

The precisions being achieved by Doppler Wobble exoplanet searches like the AAPS are being continually improved. New planet discoveries are being made at lower and lower masses, corresponding to lower and lower Doppler amplitudes, requiring that planet search teams understand the noise behaviour of their target stars in some detail, because it is the Doppler noise produced by those stars (or rather by their surface inhomgeneities and intrinsic oscillations) that are now a limiting factor.

We therefore need to develop better ways in which to parametrise the surface inhomogeneities of stars, preferably using the spectra we obtain from our Doppler search programs.

One area that has not been explored to date is the use of Doppler Imaging codes. These codes have been developed to tackle a different problem, which is to use many observations of the spectrum from a star, as it rotates, to acquire a tomographic data set, that can then be used to deconvolve back to the 'map' of variations on the stellar surface. Basically these codes track small deviations from the overall spectral line shape that the star would have in the absence of any surface variations. As the star rotates these deviations move across each spectral line, and with enough data on enough spectral lines, you can solve the inverse problem and map the stellar surface.

Figure (due to Strassmeier 2006) showing how dark regions on a stellar surface can map to changes in the shape of a spectral line. Of course, such changes can also produce artifical Doppler planet signals! We would like to be able to quantify the extent to which this takes place.

For Doppler wobble experiments we are interested in the extent to which such surface variations can produce artificial overall radial velocity changes. So while the 30-100 observations made of our Doppler host stars could not possibly be used to obtain a tomographic map, they can be used to estimate the extent to which line variations occur, and to quantify their impact on our over Doppler velocities.

There is scope for a PhD student with a strong data processing and computation background to explore the use of these Doppler Imaging techniques as a means of quantifying the impact of surface variations on Doppler planet detections.

This page last updated by Chris Tinney, 14 February 2011