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.








Exploiting the FunnelWeb Survey


The FunnelWeb survey will start operation in 2016, and will undertake a ground-breaking survey of all of the bright stars in the Southern Sky. It is remarkable that the brightest stars – while the easiest to observe – have remained amongst the most poorly characterised. The largest extant all-sky spectroscopic star catalogue (the Henry Draper Catalogue with ~ 300,000 stars) was compiled using photographic material between 1918 and 1936 and extends down to only 9th magnitude. However, over the last 2 decades the focus of the highest priority science in astronomy has shifted to exactly this range between 9th and 14th magnitude. The time is therefore right for a major survey that can target these stars.


The FunnelWeb survey seeks to create the "HD Catalogue of the 21st century" by obtaining a spectrum for every stars in the southern sky down to I=12, supplemented by a spectrum of every object that might be an M-dwarf down to I=14.


This is made possible by the TAIPAN spectrograph using the revolutionary new Starbug technology developed at the Australian Astronomical Observatory. TAIPAN can reposition its 150 on-sky apertures for the observation of a new field of targets in just minutes. This enables observations of large numbers of fields with short exposures so that TAIPAN can obtain moderate-resolution spectroscopy (λ/Δλ ≈ 2300) for huge numbers of bright stars. This capability makes possible a survey of unprecedented scale and scope in just a few years, obtaining spectra for millions of stars distributed over the entire sky accessible from the South.






Click on the image to download a Quicktime Movie showing the prototype starbugs positioning.








FunnelWeb will provide critical input data for a variety of exoplanetary science projects

  1. 1. The Hunt for Young Stars suitable for use as direct imaging targets for exoplanets.

  2. 2. Provision of Sun-like Target stars for the NASA TESS mission, delivering short-period transiting gas- and ice-giant planets suitable for follow-up to determine masses, densities, and spin-orbit alignments.

  3. 3. Provision of M-dwarf target stars for the NASA TESS mission, delivering transiting low-mass planets in the habitable zones of low-mass stars.

  4. 4.Plus a Plethora of Galactic Structure, Binary star and Serendipitous Science



PhD projects will be available in several high-impact areas making use of FunnelWeb data





FunnelWeb 1 : The Hunt for Young Stars


Astrophysics has been revolutionised by the detection of exoplanets. However most of these have been discovered by indirect techniques that see the impact of a planet on its star, rather than the planet itself. The reasons for this are straightforward – stars are very bright and planets are very dim, and they both lie very close to each other on the sky. The technologies able to remove the “glare” from around stellar images and uncover the faint planets lurking therein have only become available within the last 10 years (Traub & Oppenheimer 2011). The few planets that have been imaged have overturned much that was previously theorised about exoplanets – e.g. the HR8799 system as recently reviewed by Oppenheimer et al. (2013). There is no question that the imaging of more planets is of the highest priority for international astronomy, leading to the implementation of major new instruments on the world’s largest telescopes (e.g. the US$25m GPI facility on Gemini and the similar SPHERE on ESO’s Very Large Telescope), as well as ambitious plans for even more advanced facilities on next-generation, billion dollar Extremely Large Telescopes.


All these instruments face a serious challenge. As exoplanets get older they cool and get fainter, so that a 4.5Gyr old planet like Jupiter emits less than half as much flux as it reflects from its host star. This makes the detection of old gas-giant planets very challenging because they are as much as 1010 times fainter than their host star. Planets around young host stars (i.e. less than 100 Myr old), however, have much higher intrinsic luminosities and so lower contrasts (~104 for 10 MJ planets), making them the preferred targets for current- and next-generation exoplanet imaging searches. Around very young stars (i.e. less than 10 Myr old) planets are detectable at even moderate contrasts (~103 for 10 MJup, 106 for 2 MJup).


But which bright stars are young? (i.e. < 100Myr old?) Age is a tremendously difficult astrophysical quantity to measure without spectroscopy (i.e. via Li abundance), and no spectroscopic survey of all the nearby bright, young stars has ever been done. As a result the surveys starting on GPI and SPHERE have at most around a thousand young stars available to search. FunnelWeb will solve this problem by using a variety of youth diagnostics to identify the ~10,000 stars in its I<12 survey less than 100Myr old, and the ~800 younger than 10Myr.




In this project you will be

  1. working with the FunnelWeb team as they prepare for the survey in 2015, developing input catalogues and data analysis techniques that can identify young stars,

  2. assisting with the initial data taking as FunnelWeb starts in 2016, and then processing data to identify a first tranches of new young stars

  3. writing observing proposals to start imaging observations of those stars in 2017. Then,

  4. reducing data and publishing results.




FunnelWeb 2 : Delivering an Input Catalogue for NASA TESS.


NASA’s Kepler mission has revolutionised our knowledge of the Galaxy’s stars and planets‡. But it has its problems, which include observing only faint stars clustered in a single northern field. Even more critically, its target stars were barely characterised when Kepler launched, and remain so to this day. Since what we know about Kepler’s planets relies on how well we understand its stars, this is a serious issue. The TESS satellite – with its all-sky survey of brighter stars that can be more readily followed up – is set to once more revolutionise our understanding of exoplanets (planets orbiting other stars). But for TESS to fully exploit its potential, its target stars must be fully characterised.



Figure: Left. | The instantaneous combined field of view of the four TESS cameras. Middle. | Division of the celestial sphere into 26 observation sectors (13 per hemisphere). Right. | Duration of observations on the celestial sphere, taking into account the overlap between sectors. The dashed black circle encloses the ecliptic pole.




FunnelWeb can obtain a high-quality spectrum for every southern star that TESS can observe, delivering an input catalogue that (a) contains no giants or double-lined spectroscopic binaries around which exoplanets cannot be found, and (b) provides a stellar temperature, surface gravity, metallicity and radial velocity in advance for every star that TESS can observe. This will make it possible to interpret TESS results on planet frequency and system architectures as a function of host star mass, age, and stellar population in a direct and rapid way that has been problematic for Kepler without the investment of hundreds of nights of large telescope time (valued at tens of millions of dollars). FunnelWeb can carry out those characterization observations in advance of TESS launching for a fraction of this cost.


In this project you will

  1. spend 2015 preparing analysis techniques for Funnelweb Spectra to identify and classify candidate FGK stars in the main I<12 sample, concentrating on the southern ecliptic pole (where TESS will observe first and get the longest orbital period coverage).

  2. FunnelWeb observing starts in 2016, so rapid analysis of the data to identify a sample to be included in the TESS input catalogue.

  3. in 2017 TESS starts observing in the southern hemisphere, and makes data public to the world, so you will be analysing first tranches of TESS data and extracting giant planet results.

  4. The systems will be observable with the AAT's CYCLOPS2 facility, so radial velocity follow-up of the transits so found will deliver masses and densities for those planets, as well as offering the potential for spin-orbit alignment measurements.





FunnelWeb 3 : Delivering M-dwarfs for a habitable-zone planet search


FunnelWeb has a second crucial role. TESS is targeting a sample of fainter low-mass “M dwarf” host stars, since these small, cool stars allow TESS to detect terrestrial-mass planets on potentially habitable orbits. To do this, TESS needs to know where all the M-dwarfs are. By observing all potential M-dwarf candidates, FunnelWeb can deliver a catalogue of ~25,000 confirmed M-dwarfs for TESS observation, putting Australian astronomers at the forefront of the search for habitable environments in exoplanetary systems.


In this project you will

  1. Spend 2015 preparing analysis techniques for FunnelWeb Spectra to identify and classify candidate M-dwarfs from the I<14 sample, concentrating on the southern ecliptic pole (where TESS will observe first and get the longest period coverage).

  2. FunnelWeb observing starts in 2016, so you will carry out rapid analysis of the data to identify an M-dwarf sample to be included in the TESS input catalogue.

  3. TESS starts observing in the southern hemisphere in 2017, and makes data public to the world, so start analysing first tranches of TESS data and publishing small planets in the habitable zones of M-dwarfs




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.








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.




This page last updated by Chris Tinney, 24 June 2014