The search for white dwarf binaries

Abstract

In this thesis, I attempt to categorize variable stars found with the OGLE telescope with the main aim being to find binaries containing white dwarfs. To do this, I combine light curve data from the OGLE telescope with data from the large Gaia EDR3 catalogue and a recently published 3-dimensional extinction map to gather the colour and absolute magnitude of the binary stars. Lastly, I use an artificial neural network offered by the phoebe binary star software to model the light curves giving precise orbital parameters that allow for categorization of the binary stars. After this data processing, I find that there are likely no double white dwarf binaries in the OGLE catalogue, while a set of 123 white dwarf and main sequence binaries is identified.

Popular Abstract

Looking at the night sky, stars appear as single bright points that paint the sky. Yet for many stars, there’s more to it. A simple amateur telescope pointed at Alpha Centauri, the second brightest light in the southern skies, reveals that the bright point is in reality composed by two stars in close proximity to each other. In the northern hemisphere, the same can be seen when looking at Albeiro in the constellation Cygnus. Such star systems, with two stars bound together by gravity and spinning around each other are called binary star systems, or simply binaries.

When compared to the size of the universe, the stars Albeiro and Alpha Centauri are very close to Earth. As the distances increase, it becomes more and more difficult, or even impossible, for our telescopes to distinguish between two separate stars. However, binary stars can also be detected through in another way. As with clouds dimming the sun, or the rarer but more accurate Lunar eclipses, an object can pass in front of another and shadow it from sight. In binary stars, the light from one of the stars can be shadowed by the other as it passes in front of it once every orbit. The result is a sudden darkening of the light from a binary, which repeats itself once every orbit.

The second key part to my bachelor project are white dwarfs, the remains of stars that run out of fire. As their name suggest, they are small, faint and white in colour, yet their masses are still quite large, leading to very dense objects. At least, this is what theoretical models tell us. But these same theoretical properties mean that studying white dwarfs has been proven difficult.

As astronomers, we cannot build our own stellar systems and observe how they fare. However, we can look at the sky, observe varied systems and see which of our theoretical models hold... and which are proven wrong. The oscillations in brightness of binary stars reveal lots of information about the binaries, from their relative temperature to their radius, affecting how long the eclipse last. We don’t know what happens to binary stars when they die. How many pairs of white dwarf binaries exist, and how they look like, is something which still poses many unknowns.

For the past thirty tears, numerous ground and space telescopes have scanned the night sky and meticulously archived their observations. When put together, they allow unprecedented precision in the identifying of stars. I will be the one taking on this challenge, combining and filtering through decades worth of data in the search for white dwarf binaries.

• author: Bravo, Gian Michele
• supervisor: Michal Pawlak; Ross Church
• organization: Department of Physics; Astrophysics
• course: FYSK04 20241
• year: 2024
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: binary stars, variable stars, white dwarfs
• report number: 2024–EXA233
• language: English
• id: 9169899
• date added to LUP: 2024-08-12 08:48:39
• date last changed: 2024-08-12 08:48:39