My Thesis in 400 Words: Farbod Jahandar

Farbod Jahandar, a PhD student at iREx, recently completed his PhD at Université de Montréal. Here he summarizes his doctoral research project.

An artist’s conception shows planets around a red dwarf star. Credit : NASA / JPL-Caltech Illustration

M dwarfs, the smallest and coolest type of stars, are also the most common type of star in our Galaxy. Studying them helps us learn a lot about stars, galaxies, and in the search for Earth-like exoplanets. During my PhD studies, my goal was to broaden our understanding of these common stars, specifically through the lens of a technique called spectroscopy.

At the core of our research is the SpectroPolarimètre InfraRouge (SPIRou), an advanced instrument located at the Canada-France-Hawaii Telescope (CFHT). SPIRou’s near-infrared spectropolarimetry is particularly effective for studying M dwarfs that primarily emit light in that portion of the electromagnetic spectrum. This capability is essential for precise determinations of fundamental properties such as temperature, surface gravity, and concentration of different elements inside stars.

Our initial investigations targeted Barnard’s star, a well-studied nearby M dwarf. We compared its near-infrared spectra to models of stellar atmospheres (the PHOENIX-ACES  models), identifying various discrepancies affecting the accuracy of elemental composition estimates. To overcome these challenges, we developed specialized software for analyzing the near-infrared spectra, taking into account uncertainties in the models. Our temperature estimates for Barnard’s star aligned closely with results from other methods (interferometric method), and we were able to determine the abundance of elements that had not been previously measured.

Our research then expanded to a sample of 31 nearby M dwarfs, including several in binary systems with more massive primary stars. This diverse group allowed us to assess the broader application of our methods, revealing insights into the comparative analysis of near-infrared and optical spectroscopy. The findings from our study, such as temperature and metallicity measurements, aligned closely with optical measurements, showcasing the accuracy of high-resolution near-infrared spectroscopy. In addition, we determined the chemical abundances of several elements, including elements crucial for modelling the interiors of potential exoplanets orbiting these stars.

My research findings contribute significantly to the field of spectroscopy, particularly in the study of M dwarfs. The outcomes of this research contribute significantly to the field of spectroscopy, particularly in the study of M dwarfs, but we have also realized we still need better atmospheric models to fully use the power of near-infrared light to understand these cool stars.

More information

Farbod completed his PhD at the UdeM between 2018 and 2023, under the supervision of Professor René Doyon (Université de Montréal, iREx) and Professor Simon Thibault (Université Laval). His thesis will be available soon.