Dennis Stello's page on astronomy

The Kepler satellite at Ball Aerospace & Technologies Corp.

I am an astrophysicist at the School of Physics at the University of New South Wales where I am heading the Stellar Oscillations Group.
To contact me see my contact details.

My main area of research is asteroseismology -- the study of stars through the interpretation of their oscillations -- which aims to understand stellar structure and evolution.
In particular, my interest and expertise are within:
 - Observation and interpretation of stellar oscillations
 - Modelling stellar evolution and pulsation
 - Solar-like oscillations
 - Stellar clusters
 - Red giant stars
 - Automatic data analysis software

Dennis Stello's publications and Resume/CV.

Main research infrastructure:
Space-based data: My main research is centred around the analysis of data from NASA's Kepler, K2, and TESS missions. My role as member of the Kepler Asteroseismic Science Consortium (KASC) and leader of two working groups involved the target selection and analysis of Kepler data. I also work on the Kepler mission's new life, called K2, which we are using for Galactic Archaeology. I am chair of the working group working on the asteroseismology of red giant stars in the TESS Asteroseismic Science Consortium (TASC).

SONG: I am part of the Stellar Oscillation Network Group, which uses ground-based high-precision radial-velocity measurement to detect the Doppler shift of stars caused by their oscillations.

M67 open cluster campaigns. I led a global multi-site observing campaign with about a dozen telescopes in Australia, Asia, Africa, Europe, North- and South America. The aim was to detect stellar oscillations on a large number of stars that were all 'born' at the same time out of the same cloud of interstellar gas. I was part of the core team that re-observed the stars with NASA's K2 mission, and led the publication reporting the team's first result. 

What is Asteroseismology?

When you blow through a trumpet, plug the string of a guitar, or move your finger across the rim of the wine glass to make it ring, you are creating standing sound waves. These sound waves depend on the physical properties of the 'ringing' object, such as its size and shape, its temperature, and what it is made of. For example, a full wine glass with water sounds differently than when it is empty. If you play a trumpet at room temperature it sounds differently than if you had just taken it out of a freezer. And while a violin and a cello look very similar you will have no trouble telling which is which purely from the sound they produce. In a similar way astronomers can obtain knowledge about the interiors of stars, like their size, temperature, and internal structure by measuring the frequencies of the oscillations caused by standing sound waves inside the stars. This technique-- called Asteroseismology -- is analogue to 'Earth'-seismology where geologists measure sound waves in the Earth triggered by earthquakes to find out what the Earth's interior is made of.

The oscillations in a star makes the star ring like a large spherical bell, with regions of compression and expansion as illustrated in the cartoon as yellow and red regions. Detecting the oscillations can be done by measuring the Doppler shift of the light from the surface of the star, which measures the speed by which the surface is literally moving in and out as the star oscillate (vibrate). The surface of a star like the Sun will only move in and out by about 100m with speeds of a few metres per second, roughly walking speed, while a more evolved star like a Red Giant will oscillate more vigorously with amplitudes 10 to 100 times larger. Another technique is to measure the brightness of the star as it changes due to the compression and expansion.  These brightness variations are of the order of a few parts per million (less than 0.001%) for a Sun-like star, and about  0.01 to 0.1% for a Red Giant.
It is truly amazing that these tiny oscillations in a star many light years away can be measured from Earth!

Listen to the sound of the stars (sound based on observed frequencies, scaled to the human audible range):
alpha Cen A  A star slightly older and bigger than the Sun.
xi Hydrae      A more massive and much more evolved red giant star, with a radius 10 times that of the Sun.
Red giant concert Starting with the sound of a small red giant you will gradually hear three stars of increasing size - entering the  "red giant concert".
Oscillation mode of star
Oscillating star (credit: DASC)

Current students:

Marc Hon (PhD: University of New South Wales)
Hafiz Mohd (PhD: University of New South Wales)
Jason Drury (PhD: University of Sydney)
Doug Compton (PhD: University of Sydney)
Joel Zinn (PhD: Ohio State University)

Previous students:
Beau Bellamy (MSc: University of Sydney)
Jason Drury (Hons: University of Sydney)
Bhuwan Ghimire (PhD: University of Sydney)
Jacob Richter (Hons: University of Sydney)
Daniel Sultmann (Hons: University of Sydney)
Julie Lykke (MSc: Aarhus University)
Enrico Corsaro (PhD: University of Catania)
Timothy White (PhD: University of Sydney)
Daniel Huber (PhD: University of Sydney)

Media and outreach:

- GPU-enhanced AI reveals the true age of old Sun-like stars (May 2017).
PhD student Marc Hon and his supervisor Dennis Stello from the University of New South Wales Sydney developed a novel image recognition technique using artificial neural networks to detect subtle differences in the frequencies of sound inside stars observed by NASA's Kepler mission. The result enabled the team to distinguish stars in different stages of their lives, something previous methods had not been able to do. This advance opens up for automated large scale analysis of thousands of stars in great detail.
NVIDIA blog post

- Stellar sounds tells us that stars align (March 2017).

An international team led by Enrico Corsaro (Catania) and joined by his previous PhD supervisor Dennis Stello from UNSW Sydney, made the surprising discovery that stars in two old stellar clusters show strong rotational spin alignment. The results suggest that the rotational energy of star forming clouds can be significant compared to their turbulent energy, which was unexpected by theory.
The Australian (press) (pdf)
Australian Geographic
Cosmos Magazine
New York Post

- Astronomers find ancient magnetic field hiding inside retired stars (January 2016).

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)

- Kepler 37-b: The smallest planet found (February 2013).

The discovery of Kepler 37-b marked the smallest planet found so far. With a size similar to our moon this was a tremendous feat; suggesting that small planets are abundant in the Galaxy. Dennis Stello and Tim Bedding at the University of Sydney helped pin down the size of the host star (Kepler 37) and hence that of the planet itself.
Science Alert

- A year of swashbuckling advances (February 2012).

The Age's annual review of the big things in the world of science anno 2011 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.
The Age

- Aging stars are slow on the outside but fast on the inside (December 2011).
Discovery of fast spinning cores in old red giant stars
ABC Science
The Sydney Morning Herald

- Asteroseismology confirms habitable Super-Earth around Sun-like star (December 2011).
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 Sydney Morning Herald
The Herald Sun

- Star quakes in hundres of stars (January 2010).
The first results from the Kepler Mission led by the team at the
University of Sydney.
ABC Radio National (TheScienceShow)

- Launch of NASA's Kepler telescope (March 2009).

The first mission to be capable of detecing Earth-sized planets orbiting distant sun-like stars.
Astronomers at
the University of Sydney will use the Kepler data to study stellar oscillations.
The Australian
ABC Science
- Northern star breathes new life
(July 2008).
After over 100 years of decline in its oscillation amplitude the Northern star takes astronomers by surprise.
ABC Science
la Repubblica
The Herald
The Scotsman

- Ultrabass Sounds of the Giant Star Xi Hya (April 2002).
The first asteroseismic observation of a star very different from the Sun.

ESO press release (ESO PR 10/02).