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Mairi O'Brien

I am a first-year PhD student in the Astronomy & Astrophysics group at the University of Warwick. My supervisor is Pier-Emmanuel TremblayLink opens in a new window. I completed my MPhys degree at Durham University in 2021.


My PhD focuses on the calibration of stellar ages using cooling white dwarfs. The evolution of white dwarfs is relatively well-understood, so white dwarfs can be used to probe stellar formation history in the disk and halo of the Milky Way.

I am creating a volume-limited sample of white dwarfs within 40pc in the Southern hemisphere, identified using GaiaLink opens in a new window EDR3. I am using X-ShooterLink opens in a new window spectra to classify the white dwarfs and determine their atmospheric composition. By fitting their atmospheric parameters, I can learn about the properties of the white dwarfs including their mass, temperature and cooling age. We need to know the spectral classification of each white dwarf so we can use pure-H, pure-He or mixed H/He model atmospheres to accurately calculate their properties. My work contributes to the overall 40pc sample of white dwarfs for which parameters such as white dwarf space density and mass distribution can be determined, so we can further understand their evolution.

In the 40pc white dwarf sample I have classified some metal-polluted white dwarfs which harbour planets or planetary remnants. The spectra enable us to determine the composition of these rocky planets.

The sample of candidate white dwarfs from Gaia is likely to be almost complete out to 100pc (Gentile Fusillo, 2021Link opens in a new window). As we obtain more spectroscopic follow-up data, I hope to extend my work and create larger volume-complete samples, which I can use to constrain the stellar formation history of the Milky Way.

Other Research Interests

For my masters project, I studied the timing properties of accreting white dwarf systems using optical data from the satellite TESSLink opens in a new window.


This year, I am a lab demonstrator for the undergraduate physics module PX152 Physics LaboratoryLink opens in a new window.

Other Interests

At Durham, I was the co-president (2019/20) and the treasurer (2020/21) of the Women in STEM society. I was also the undergraduate representative for three years for the Durham physics ED&I group. I am committed to promoting diversity in STEM, and I am currently a mentor to two undergraduate women studying physics.

I also chair the weekly white dwarf meetings at Warwick.



S. Scaringi et al. “Localized thermonuclear bursts from accreting magnetic white dwarfsLink opens in a new window". In: Nature 604, 447–450 (Apr. 2022). DOI: 10.1038/s41586-022-04495-6. arXiv: 2204.09070 [astro-ph.HE]

Write to:

Mairi O'Brien,

Department of Physics,

University of Warwick,

Coventry CV4 7AL



Email: Mairi.O-Brien[at]
Office: PS0.04, Physical Sciences