My Thesis in 400 Words – William Frost

William Frost, a master’s student at iREx, recently completed his master’s degree at the Université de Montréal. Here he summarizes his research project.

Brown dwarfs are objects generally more massive than the largest gas planets, but strictly less massive than the smallest stars. The key difference between brown dwarfs and stars is that stars have enough mass to sustain nuclear fusion, turning hydrogen into helium and shining brightly for millions or billions of years. Brown dwarfs, on the other hand, can’t sustain fusion and mostly emit leftover energy from their formation. Over time, they become cooler and dimmer.

This artist’s concept shows a brown dwarf with bands of clouds, thought to resemble those seen at Neptune and the other outer planets. Photo Credit: NASA/JPL-Caltech

To understand brown dwarfs, scientists often need to model their light to determine properties like mass, age, size, and surface temperature. While existing models have been good at matching observations, the physical properties they predict are hard to confirm without independent measurements. To get these, we need to observe brown dwarfs closely orbiting a star, which is rare enough that astronomers call it the “brown dwarf desert.” What’s more, they need to orbit in the right orientation so that we can observe them passing in front of and behind their star.

My thesis involved studying one of these rare eclipsing brown dwarfs: LHS 6343 C. Previous studies had already published mass and radius measurements independent of models, but its other physical properties were 100% dependent on them. Using observations from the Kepler, Hubble and Spitzerspace telescopes, I was able to construct the most complete emission spectrum available for this brown dwarf. This made it possible to measure its luminosity and surface temperature with much less reliance on models.

With this information, I was able to test not only which models best reproduced the observed light from LHS 6343 C, but also which ones predicted the correct physical parameters! Such tests are quite rare and valuable, as they allow researchers to see what works and what can be improved. The atmospheres of brown dwarfs can also serve as powerful analogues for those of the giant gas exoplanets discovered today. However, the discovery of many more eclipsing brown dwarfs is needed to fully test the atmospheric and evolutionary processes these models seek to reproduce.

More information

William completed his master’s degree between 2022 and 2024, under the supervision of iREx professor René Doyon, also under the supervision of Loïc Albert. His thesis will be available soon online.