White dwarfs, planetary debris and fundamental physics


   Department of Physics and Astronomy

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  Prof M Barstow  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

White dwarfs are the end products of the life cycles of more than 90% of all stars. This makes them important laboratories for studying stellar evolution and the behaviour of matter at extremes of temperature and density. We can study the population of white dwarfs to map out the history of star formation in our Milky Way galaxy. There is growing evidence that many white dwarfs are swallowing up debris from, now destroyed, planetary systems. Measuring the abundance of this material in the atmospheres of the white dwarfs can tell us about the composition of these planets. However, we first need to understand the evolution of white dwarfs, including the composition of their atmospheres. We are using data from a variety of space missions and telescopes to study the population of white dwarfs to provide this insight.

 We wish to appoint an enthusiastic PhD student to contribute to the exploitation of this data, drawn from several observational programmes. The work will involve the analysis of spectroscopic and imaging data from the ESA Gaia mission, Hubble Space Telescope (HST) and ground-based telescopes. There will also be a theoretical element to the work, using the University’s supercomputer to simulate stellar atmospheres, for comparison with the data.

 There are several lines of research in which the student can become involved, depending on personal interests:

 We are closely involved in the European Space Agency Gaia mission. Launched in December 2013, the satellite is carrying out a detailed survey of the entire visible galaxy to measure the positions, space motion and distances of approximately 2 billion stars. Recent data releases, have yielded a sample of 100,000 white dwarfs with low resolution spectra and approximately 800,000 binary star systems, many of which will have white dwarf companions. Combine with follow-up data from other surveys and ground-based spectroscopy, the Gaia data will allow us to characterise the white dwarfs, obtain measurements of masses and radii of unprecedented accuracy, search for hidden stellar/exo-planet companions and search for the elusive progenitors of type Ia supernova explosions.

 Measurement of the abundances of C and Si in a large sample of white dwarfs shows that in all cases C is depleted, indicating that the material has a rocky origin – similar to that of asteroids. A likely explanation is that this material is collected from extra-solar planetary debris and then retained in the hot white dwarf’s envelope by the force of radiation. We now need to test this by adapting the atmospheric modeling computer programme to include these physical processes.

 Recently, we have shown that high spectral resolution and signal-to-noise spectra of a single hot white dwarfs can be used to measure potential changes in the value of the fundamental physical constants, such as the fine structure constant and electron/proton mass ratio, in a strong gravitational field. The accuracy of the technique is limited by how well we know the wavelengths of atomic absorption features in the spectrum. We have acquired improved atomic data and more high-quality spectra of other stars to continue this work.

A particular challenge of these projects is to handle a large quantity of data and models efficiently. This is likely to require the development of automated processing tools and application of artificial intelligence techniques. Therefore, a candidate with strong programming skills will be welcomed.

Enquiries to project supervisor [Email Address Removed] or [Email Address Removed]

TO APPLY

Refer to our website: https://le.ac.uk/study/research-degrees/funded-opportunities/stfc


Physics (29)

Funding Notes

The projects listed are in competition for STFC funding. Usually the project which receives the best applicant will be awarded the funding.
The STFC studentship provides:
A full UK fee waiver for 3.5 years*
An annual tax free stipend (currently £18,622 for 2023/4) for 3.5 years
Research Training Support Grant (RTSG)
Conference Fees and UK Fieldwork fund
*Up to 2 international studentships are available and include a 3.5 year full overseas fee waiver and stipend as above.

References

M.A. Barstow, J.K. Barstow, S.L. Casewell, J.B. Holberg and I. Hubeny, 2014, “Evidence for an external origin of heavy elements in hot DA white dwarfs”, MNRAS, 440, 1607-1625. (May, 10.1093/mnras/stu216). 205.
S.R.G. Joyce, M.A. Barstow, S.L. Casewell, M.R. Burleigh, J.B. Holberg and H.E. Bond, 2018, “Testing the white dwarf mass-radius relation and comparing optical and far-UV spectroscopic results with Gaia DR2, HST, and FUSE”, MNRAS, 479, 1612-1626 (September – DOI 10.1093/mnras/sty1425).
J.C. Berengut, V.V. Flambaum, A. Ong, J.K. Webb, J.D. Barrow, M.A. Barstow, S.P. Preval and J.B. Holberg, 2013, “Limits on the dependence of the fine-structure constant on gravitational potential from white dwarf spectra”, Phys.Rev.Letters, 111. http://arxiv.org/abs/1305.1337
Gaia Collaboration; P. Montegrifo, M. Bellazzini, F. de Angeli, R. Andrae, M.A. Barstow, et al., 2022, “Gaia Data Release 3: The Galaxy in your preferred colours. Synthetic photometry from Gaia low-resolution spectra”, A&A, 674, A33. arXiv:2206.06215
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