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Sirius Binaries
Prof Martin Barstow and Dr Matt Burleigh, X-ray and Observational Astronomy
Supervisor : Prof Martin Barstow (mab@le.ac.uk) and Dr Matt Burleigh (mbu@star.le.ac.uk)
Details of Project
Sirius is a nearby binary system consisting of a bright main sequence A star and a white dwarf companion in an approximately 50 year orbit. Historically, Sirius B is important as one of the first white dwarfs to be discovered, and its nature could only later be explained by the development of quantum mechanics and general relativity. Today we can use Sirius and similar binaries to test fundamental physics, such as the relation between an electron degenerate white dwarf's mass and its radius, and the relation between a white dwarf's mass and the mass of its progenitor star. In turn, this helps to determine the fraction of a star's mass that is returned to the interstellar medium to eventually form a new generation of stars. Binaries that include a white dwarf are also thought to be the progenitors of Type Ia supernovae, which were integral to the Nobel-prize winning discovery of Dark Energy. However, no bona fide SNIa progenitor has ever been found.
The Sirius system is easy to study because it is nearby. For more distant stars, it is increasingly difficult to know if they too have white dwarf companions. Indeed, we are in fact highly ignorant of the true population of white dwarfs in Sirius-like binaries. In the past, xray surveys and ultraviolet spectroscopy have found a few dozen examples. But these only find the hottest white dwarfs. More common cooler examples are extremely hard to spot.
- Credit: NASA, ESA G. Bacon (STScI)<br /> http://www.spacetelescope.org/images/html/heic0516b.html<br />
Intriguingly, a few stars that are known to have extra-solar planets also have white dwarf companions. These white dwarfs can be used to estimate the age of the system and its planets, and thus allow us to constrain more about the evolution of those solar systems than would normally be possible.
We would like to hire an enthusiastic PhD student to undertake a project on Sirius binaries. Using ultraviolet all-sky surveys like GALEX, adaptive optics imaging, and surveys for proper motion companions to stars, you will search for new Sirius systems. You will study these binaries in detail using spectra from satellites like the Hubble Space Telescope and ground-based telescopes like the VLT.
These studies are important to undertake over the next few years as we look forward to the launch of the European Space Agency's GAIA mission. GAIA will precisely determine the distances to thousands of Sirius systems, allowing us to finally make detailed investigations of both the population of white dwarfs hidden in binaries, and the fundamental physics of electron degenerate matter.
