Extrasolar Planet Search Projects

UNSW has an active and growing group of researchers using various methods to search for extrasolar planets, including tranist, radial velocity, and direct imaging. UNSW researchers have also worked on planet-finding projects in microlensing and polarimetry. Close collaboration with renowned planet hunters around the world places UNSW at the forefront of extrasolar planet research.

The Exoplanetary Science group is searching for planets via radial velocity using the 3.9m AAT at Siding Spring Observatory, via high-resolution imaging using the 8m Gemini South 8m, and via direct imaging using the 8m Very Large Telescope and 3.9m AAT. The APT group searches for transiting exoplanets using the 0.5m Automated Patrol Telescope at Siding Spring Observatory. The LAPCAT group is designing the Large Antarctic Plateau Clear-Aperture Telescope to search for exoplanets via direct detection from Antarctica.

We are always looking for new honours and postgrad students to work on various apects of our planet hunting projects and welcome you to join our group. To learn more, explore our projects below. If you are interested in working with one of our research teams, contact Chris Tinney about working with the Exoplanetary Science group, Michael Ashley about the APT group, or John Storey for the LAPCAT group,






The Exoplanetary Science Group: Understanding Exoplanets

The vast majority of the 400-odd exoplanets we have detected to date have been found by the "Doppler wobble" method. This detection technique relies on the fact that as planets orbit their host star, their gravitational pull cuases the star to move in a tiny orbit or "wobble" of its own. This can be detected via the Doppler Effect - when the star is moving away from the earth, the light coming from it will be blue shifted, while when the star is moving towards the earth it will be redshifted (see right).

The size of this effect is very small - the Doppler wobble induced by typical Jovian-sized planets is in the range 1-100m/s. To detect such small velocity changes requires using some of the world's most advanced spectrographs on very large telescopes. Even so the Doppler shifts measured represent shifts of ~20 silicon atoms on the surface of our optical detectors!

The Anglo-Australian Planet Search has been operating on the Anglo-Australian Telescope since 1998. It has demonstrated the worlds highest long-term velocity precision, and with over 30 planets detected from its target list of ~240 stars has the highest success rate of any international Doppler search, detcting mroe than 30 planets from its 240-odd target stars.

Other activities of Prof. Tinney's group at UNSW include using the advanced Gemini NICI coronagraph to search for companions to our AAPS target stars; using methane imaging programs on the 3.9m AAT and 8m VLT to detect "unbound" planets in nearby young star clusters; infrared and optical parallax programs targeted at brown dwarfs; follow-up of cool T- and Y-dwarfs discovered in the 2MASS and UKIDSS databases.

For more information on the Exoplanetary Science group's activities and projects for new students, visit our home page.

  THE AAPS TEAM

    Collaborators
AAPS PUBLICATIONS
Visit the Anglo-Australian Planet Search page for a list of our discovery papers and associated publications.



The APT Group: Searching for planets via Transit

Over two hundred planets are now known to be orbiting stars other than the Sun (see http://exoplanets.org/almanacframe.html for a list). Most of these planets were detected using the radial velocity method, which involves measuring (using spectroscopy) the "wobble" of the star due to the planet's gravitational pull. An alternative used by an increasing number of planet searches is the transit method (see figure below). This involves measuring the small decrease in apparent brightness (of order 1%) of the star, as the planet eclipses (or transits) it. This method is thus only sensitive to planets with edge-on orbits. However, if such a planet is detected, its size, mass and orbital characteristics can be determined (with follow-up spectroscopy), constraining models of its structure and formation.

High-precision spectroscopic observations of a host star during a known transit may reveal something about the chemical composition of the planet's atmosphere. The first such observation was recently made by Charbonneau et al. (2001). Under highly favourable circumstances, it may even be feasible to search for the presence of atmospheric oxygen (Webb & Wormleaton, 2001).

For the transit method to be effective, two main difficulties need to be overcome. Firstly, the probability that a given star hosts a planet in an edge-on orbit and the transit occurs while the star is being observed is low. Thus, a reasonable detection rate can only be achieved by continuous photometric monitoring of a large sample (tens of thousands) of stars. A wide-field automated telescope is ideal for this task.

The second challenge is the high level of photometric precision required. Changes in brightness on timescales of a few hours need to be measured to better than 1% precision. This is difficult to achieve with CCD photometry on ground-based telescopes (the only feasible method for most transit searches). Above the fundamental limits set by Poisson statistics (since measurement involves counting photons in the image), systematic errors become important.


The Automated Patrol Telescope

The Automated Patrol Telescope (APT) is a 0.5m telescope owned and operated by the University of New South Wales, and located at Siding Spring Observatory, Australia. The CCD camera images a 2x3 degree field with 9.4 arcsecond pixels. The telescope is entirely computer-controlled, with the possibility of remote or fully automated observation. An important drawback of using a wide-field telescope is that the images tend to be undersampled (as is the case with the APT). Because the sensitivity of a CCD is not uniform over the surface of a single pixel, the total brightness measured for a star is dependent on where the star falls relative to pixel boundaries. This becomes significant in undersampled images, where the light from a star is spread over only a few pixels. For the APT, this effect proved to be the limiting factor, causing photometric errors of several percent.

We have developed a new observing technique specifically aimed at minimising the effects of intra-pixel variations. We systematically move the telescope during intergration, in a raster-type scan covering 1x1 or 2x2 pixels. Although this does broaden the PSF slightly, it effectively eliminates the intra-pixel variation problem. The resulting PSF is fairly flat topped with a very rapid falloff. We therefore developed an optimised aperture photometry package to process the resulting images, with co-located apertures for each object positioned to better than 1/100th of a pixel repeatability in each frame.  Using this system we are obtaining differential photometric precision of ~2mmag down to V=11 in 150sec exposures. The lightcurves are further processed to find and remove periodic signals from variable stars and searched for transit signals using a variant of the Gregory-Loredo algorithm optimised for transit detection.


THE APT TEAM
    Current Members

    Collaborators

    • Dr. Marton Hidas (University of California-Santa Barbara)
    • Dr. Mike Irwin (IoA, Cambridge)
    • Dr. Suzanne Aigrain (IoA, Cambridge)


APT PUBLICATIONS
Hamacher, D.W.; Hidas, M.G.; Christiansen, J.L.; Ashley, M.C.B.; Britton, T.R.; Curran, S.J.; Webb, J.K.; Young, T.B.
The University of New South Wales Extrasolar Planet Search: planets selected from fields observed between 2004 and 2007
Monthly Notices of the Royal Astronomical Society, submitted April 2008

The University of New South Wales Extrasolar Planet Search: a catalogue of variable stars from fields observed between 2004 and 2007
Christiansen, J.L.; Derekas, A.; Kiss, L.L.; Ashley, M.C.B.; Curran, S.J.; Hamacher, D.W.; Hidas, M.G.; Thompson, M.R.; Webb, J.K.; Young, T.B.
Monthly Notices of the Royal Astronomical Society, Volume 385, Issue 4, pp. 1749-1763

The first high-amplitude delta-Scuti star in an eclipsing binary system
Christiansen, J.L.; Derekas, A.; Ashley, M.C.B.; Webb, J.K.; Hidas, M.G.; Hamacher, D.W.; Kiss, L.L.
Monthly Notices of the Royal Astronomical Society, Volume 382, Issue 1, pp. 239-244

A new detached K7 dwarf eclipsing binary system
Young, T.B.; Hidas, M.G.; Webb, J.K.; Ashley, M.C.B.; Christiansen, J.L.; Derekas, A.; Nutto, C.
Monthly Notices of the Royal Astronomical Society, Volume 370, Issue 3, pp. 1529-1533. (08/2006)

The University of New South Wales Extrasolar Planet Search: methods and first results from a field centred on NGC 6633
Hidas, M. G.; Ashley, M. C. B.; Webb, J. K.; Irwin, M.; Phillips, A.; Toyozumi, H.; Derekas, A.; Christiansen, J. L.; Nutto, C.; Crothers, S.
Monthly Notices of the Royal Astronomical Society, Volume 360, Issue 2, pp. 703-717. (06/2005)

Searching for Extrasolar Planets from UNSW
Christiansen, Jessie L.; Ashley, M. C. B.; Hidas, M. G.; Webb, J. K.; Phillips, A.; Irwin, M.; Irwin, J.
Direct Imaging of Exoplanets: Science & Techniques. Proceedings of the IAU Colloquium #200, Edited by C. Aime and F. Vakili. Cambridge, UK: Cambridge University Press, 2006., pp.193-198

PROCEEDINGS
Searching for Extrasolar Planets from UNSW
Christiansen, J. L.; Ashley, M. C. B.; Webb, J. K.; Hidas, M. G.
Protostars and Planets V, Proceedings of the Conference held October 24-28, 2005, in Hilton Waikoloa Village, Hawai'i. LPI Contribution No. 1286., p.8191 (2005)

Searching for Extrasolar Planets Using Transits
Hidas, M. G.; Webb, J. K.; Ashley, M. C. B.; Lineweaver, C. H.; Anderson, J.; Irwin, M.
Bioastronomy 2002: Life Among the Stars, Proceedings of IAU Symposium #213. Edited by R. Norris, and F. Stootman. San Francisco: Astronomical Society of the Pacific, 2003., p.77 (06/2004)

An Automated Search for Extrasolar Planet Transits
Hidas, M. G.; Webb, J. K.; Ashley, M. C. B.; Lineweaver, C. H.; Anderson, J.; Irwin, M.
Scientific Frontiers in Research on Extrasolar Planets, ASP Conference Series, Vol 294, Edited by Drake Deming and Sara Seager. (San Francisco: ASP) ISBN: 1-58381-141-9, 2003, pp. 383-386

High-Precision Lightcurves from Undersampled CCD Images
Hidas, Marton G.; Ashley, Michael C.; Webb, John K.; Irwin, Michael; Aigrain, Suzanne; Toyozumi, Hiroyuki
Solar and Solar-Like Oscillations: Insights and Challenges for the Sun and Stars, 25th meeting of the IAU, Joint Discussion 12, 18 July 2003, Sydney, Australia (2003)





The LAPCAT Group: searching for planets via Direct Imaging (proposal and design phase)

LAPCAT The Large Antarctic Plateau Clear-Aperture Telescope (LAPCAT) is a preposed 8.4 metre off-axis optical/IR telescope to be located at Dome C, Antarctica. One of the primary science drivers for LAPCAT will be to directly image exo-planets. The high thermal infrared sensitivity, the high level of correction achievable with its adaptive optics system, and the telescope optical configuration make LAPCAT uniquely capable for such science.

The primary source of noise for exo-planet imaging at close angular separations arises from scattered starlight at the position of planet. Traditional coronagraphic and apodisation techniques can suppress the stellar PSF, but have significant limitations in the achievable resolving power and throughput. Techniques currently being investigated, such as the Phase-Induced Amplitude Apodization Coronograph (PIAAC) proposed by Guyon et al.(2005), should allow stellar suppression to inner working angles of several times the diffraction limit with very high efficiency. This equates to 3.5 AU at 10 pc for M band imaging with LAPCAT. Although apodised pupil masks can be used to suppress spider vane diffraction in Lyot coronographs, residual spider diffraction increases noise and can effect speckle statistics. The PIAAC technique is likely to suffer from similar limitations, and thus the un-obscured primary of LAPCAT is advantageous.

In a 24 hour integration, LAPCAT should detect a 1.2 Mjup 1 Gyr old planet at 10 pc, or a more mature 5 Gyr planet of 4.2 Mjup. These are significantly lower masses than are detectable with existing facilities, and arecomparable with the detection limits of future Extremely Large Telescopes at mid-latitude sites. Younger (100 Myr) Jupiter mass planets at very wide (20 AU) orbits should be detectable with LAPCAT out to 60 pc. LAPCAT thus provides a significant extension of the parameter space of other planet detection methods. The higher spatial resolution of ELT class telescopes will enable imaging of planets at closer orbits than LAPCAT. An ELT located in Antarctica would thus be an exceptionally powerful facility for this science.

THE LAPCAT TEAM


LAPCAT PUBLICATIONS
LAPCAT: the Large Antarctic Plateau Clear-Aperture Telescope
Storey, J. W. V.; Angel, R.; Lawrence, J.; Hinz, P.; Ashley, M. C. B.; Burton, M. G.
Astronomy in Antarctica, 26th meeting of the IAU, Special Session 7, 22-23 August, 2006 in Prague, Czech Republic, SPS7, #31 (08/2006)

LAPCAT: the Large Antarctic Plateau Clear-Aperture Telescope
Storey, John; Angel, Roger; Lawrence, Jon; Hinz, Phil; Ashley, Michael; Burton, Michael
Ground-based and Airborne Telescopes. Edited by Stepp, Larry M.. Proceedings of the SPIE, Volume 6267, pp. 62671E (07/2006)

What a really big Antarctic telescope could achieve
J. W. V. Storey, M. C. B. Ashley, M. G. Burton and J. S. Lawrence

LAPCAT: A LARGE, OFF-AXIS OPTICAL/INFRARED TELESCOPE FOR DIRECT IMAGING OF PLANETS AROUND OTHER STARS
J.W.V. Storey, J.R.P. Angel, J.S. Lawrence, P. Hinz





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We are grateful to SUN Microsystems Australia for generously providing computing equipment in support of the APT project


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