The University of Sydney's involvement in the NASA Kepler mission

Kepler logo

Johannes Kepler: 1571-1630       

Picture of Kepler satellite

Oscillation mode of star

The Kepler satellite at Ball Aerospace & Technologies Corp.


- Jan 2016: Astronomers find ancient magnetic field hiding inside retired stars
A team led by Dennis Stello, and including Daniel Huber and Tim Bedding, from the University of Sydney has found that strong magnetic fields in the cores of stars are common.

ABC AM (radio)
ABC 1 (TV) news report (download) (youtube)
The Australian (press)
La Repubblica (press)

- Feb 2012: A year of swashbuckling advances
In his annual review of the highlights from the world of science anno 2011, journalist Peter Spinks from one of Australia's leading news papers (The Age) summarises what were the big things that made it into his top eight. In the article he gives special mention to astrophysicists Dennis Stello and Tim Bedding at the University of Sydney and their recent results on the asteroseismology of a planet hosting star.

- Dec 2011: Stellar oscillations reveals differential rotation inside red giant star
A team of astrophysicists including the University of Sydney's Dennis Stello and Tim Bedding managed to look inside old stars and discovered that their cores spin at least ten times faster than their surfaces. The result was published in the prestigious journal Nature.

ABC Science
The Sydney Morning Herald

- Dec 2011: Kepler finds habitable Super-Earth around Sun-like star
The team at the University of Sydney used data from NASA's Kepler Mission to measure the mass and size of the planet hosting star Kepler 22 and found it to be almost identical to the Sun.  The size of star allowed the Kepler team to obtain a precise size of the planet as well, which turned out to be only 2.4 times the size of Earth and with an orbital period of 290 days, making this planet-star system more similar to the Earth-Sun system than any other found thus far.


The Sydney Morning Herald
The Herald Sun

- Feb 2011: Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
A large team led by University of Sydney's Prof Tim Bedding discovered that mixed modes with g-mode character could be used to distinguish between otherwise similar red giant stars.  This breakthrough published in the journal Nature demonstrates that stars that look the same on the surface are distinctly different in their cores dependent on whether they only burn hydrogen in shell or also helium in the core.

- Oct 2010: Kepler reveals that all red-giant stars oscillate due to huge 'star quakes'
In a recently published paper lead by University of Sydney PhD student Daniel Huber, scientists have announced the discovery of stellar oscillations in about 1000 red-giant stars in the Kepler field. Many of the red giants are relics of stars that once where like the Sun, which will itself become a giant when it's hydrogen fuel gets exhausted in roughly 5 billion years from now. Kepler data has now revealed that red giants in all evolutionary states show 'star quakes', which allowed the team to determine the properties of these aged stars and hence improving our understanding of the future of our Sun.

Listen to the red giant concert: In this audio file you will hear oscillations based on actual frequencies that were measured by Kepler - scaled to audible range
of the human ear. Starting with the sound of a small red giant you will gradually hear three stars of increasing size - each with lower
frequencies, but higher amplitudes - entering the  "red giant concert"

star sizes

Figure (Top): Comparison of the size of the Sun to the smallest and largest red-giant for which oscillations have been detected with Kepler. Never before have star-quakes been discovered in such a wide variety of red-giant stars.

Figure (Right): A plot of the dominant oscillation frequency versus temperature for all red-giant stars in which oscillations have been detected (open diamonds). Open squares show the position of bright, unevolved stars (including the Sun) for which oscillations had been detected prior to the Kepler mission.

nu_max versus Teff diagram
Voice of America
Science News

- Jan 2010:
Stellar oscillations from 'star quakes' detected in open cluster stars
A group of more than 50 scientist headed by University of Sydney astronomer Dennis Stello detected - for the firts time - oscillations in stars that formed simultaniously from one big cloud of gas and dust into a large cluster of stars about 2.5 billion years ago. The stars in the open cluster NGC6819 showed clear oscillations similar to those we see in the Sun. Despite all the stars in this cluster were born as siblings, the Kepler date unfold clear differences between each star (see Figures below).

Figure (Top): Stars in the cluster NGC6819 in a brightness versus temperature diagram. As stars age they move from the lower left to the upper right in the diagram (white arrows). Stars in a cluster are formed at the same time but with different masses. Although the stars share a common age we see some stars (less massive) down at the bottom, while others (heavier stars) have already become red giants (top right) because heavier stars age faster. The insets show Kepler data of the stellar oscillations, which reveal the increasing size of the stars towards the top right of the diagram with larger stars having longer oscillation periods (corresponding to lower frequency, or pitch. See figure to the right).

Figure (Right): So-called Fourier spectral representation of the Kepler data for 10 selected stars in the cluster NGC6819, which show the power of the oscillations over a large range of frequencies. The location of the oscillation frequencies are marked by vertical dotted lines. The stars are sorted in brightness with the brightest at the top. The large and bright red giants show lower oscillation frequencies than the smaller giants at the bottom.

- Jan 2010: Unversity of Sydney astronomers takes the pulse of red giant stars
Led by Tim Bedding a large team of astrophysicists were able to show new exciting results on stellar oscillation from the analysis of hundreds of stars observed by Kepler during the first month of science operation. The team were able to detect a characteristic frequency separation of the osciilations that potentially can be used to determine the age of the stars.

Searching for new worlds
Kepler is a NASA satellite built by Ball Aerospace & Technologies Corp. Its main aim is to detect planets around other stars in their habitable zone, not to close nor too far from the star for liquid water to exist on the surface. Kepler will do that by measuring the planet transits, which are tiny dips in the star light as the planet moves across the stellar disk -- partially eclipsing the star.

Figure based on one by Hans Deeg, from 'Transits of Extrasolar Planets'
Move mouse over figure to view animated transit (884 K continuous loop GIF, requires JavaScript to be enabled); Click on figure to view or download MPEG animation (783 K). problem?

The dimming of the light caused by a Jupiter sized planet moving across a Sun-like star is about 1%, while an Earth-sized planet will only block less than 100 parts per million (0.008%). The duration of a transit is about 10 hours long.

The photometric precision of the telescope will enable scientists to detect the first Earth-sized planets around Sun-like stars, and determine if such Earth twins are common. To enable this feat Kepler will monitor more than 100,000 stars continuously for the next 3.5 years, like looking for needles in a haystack. Fortunately, Kepler is equipped with big eyes -- a 95 Mega Pixels CCD mosaic -- which will stare at the same patch of sky in the constellation the Swan (Cygnus) near the plane of the Milky way.

Kepler FOV Kepler View
Kepler CCDs
Kepler field of view on the sky
Kepler viewing zone (artist's impression)
The Kepler eyes

For more information on the planet search aspects of the mission see the NASA Kepler Home page or the other relevant links at the bottom of this page.

Exploring the inside of stars
The exquisite detail provided by the Kepler measurements will also be used to detect oscillations in the stars, work that involves more than 200 scientists around the world through the Kepler Asteroseismic Science Consortium (KASC) including  the Stellar Oscillations Group at the Sydney Institute for Astronomy (SIfA). From studying the stellar oscillations -- called asteroseismology -- we can explore the interior of stars, providing a new dimension to the study of stellar structure and evolution. While this is a quite fascinating field in its own right, asteroseismic investigation can also give additional perspectives to other fields of astrophysics that relate to stars, such as planet formation and evolution.

Synergies between stars and planets
Since the Kepler data are used for both planet search and asteroseismology there is an obvious synergy, which we intent to exploit. Kepler applies asteroseismology as a tool to constrain the properties of the stars around which planets are being detected. In particular, the size of the stars is imprinted in the stellar oscillations and can therefore be deduced from asteroseismolgy, which will aid the determination of the size of the transiting planets.
Software has been developed by members of our group in Sydney to determine the size of stars, and is part of the analysis package used to core team analysing the planet hosting stars.

Who are we?
The Stellar Oscillations Group at SIfA is involved in the target selection and analysis of Kepler data. Stars that we are particularly interested in are solar-like stars, M- and K-giant stars, oscillating stars in eclipsing binary systems and stellar clusters. Our group members are: Tim White, Dennis Stello, Charles Kuehn, Othman Benomar, and Tim Bedding.

A transit of a giant planet in orbit around a giants can look very similar to
a transit of a small Earth-sized planet around a Sun-like star.

Kepler launch
Launch Vehicle:    
United Launch Alliance Delta II Rocket googleearth1googleearth2
Launch Site:  
Kennedy Space Center, Cape Canaveral Air Force Station (Florida)
- Launch Complex 17 - Pad 17-B

Launch Time: 

6 March, 2009, 22:49 EST (local time in Florida),
7 March, 2009,  03:49 (UT),
7 March, 2009, 14:49 Australian EST.

Satellite Orbit:

Kepler follows an Earth-trailing orbit around the Sun, with a
period of 53 weeks, one week more than Earth.

Mission length:
3.5 years, but can be extended by 2.5 years, after which it become
difficult to down link the data due to its distance from Earth.

Kepler orbit
Kepler orbit

To view the launch go on youtube or NASA mission page.
After one minute the solid boosters (in red) were ejected

Useful links
Kepler Home page (Information about the planet search program)
Danish Asteroseismology Centre (Information about the Kepler Asteroseismic Investigation)
NASA mission page (NASA media release and information about launch)
Ball Aerospace & Technologies Corp. (Pictures of the satellite during construction)
NASA TV (Launch broadcast)
Kepler Asteroseismic Science Consortium
Kepler on Wikipedia

For more information contact Dennis Stello