I am an astrophysicist at the School of
Physics at the University of Sydney where I am part of the Stellar
Group at SIfA.
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
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
campaign. 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.
|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, if you fill the wine glass with water it sounds differently than when it is empty. If you play the 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 make. In a similar way astronomers can obtain knowledge about the interiors of stars, like their size, temperature, and composition 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 surface of the star, which measures the speed by which the surface is literally moving in and out as the star oscillate. 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 on a star many light years away can be measured from Earth!
Oscillating star (credit: DASC)
Bhuwan Ghimire (PhD: University of Sydney)
Beau Bellamy (MSc: University of Sydney)
Jacob Richter (Hons: University of Sydney)
Jason Drury (PhD: University of Sydney)
Doug Compton (PhD: University of Sydney)
Daniel Sultmann (Hons: University of Sydney)
Daniel Huber (PhD: University of Sydney)
Julie Lykke (MSc: Aarhus University)
Enrico Corsaro (PhD: University of Catania)
Timothy White (PhD: University of Sydney)
Jason Drury (Hons: University of Sydney)
Media and outreach:
- 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).