Olivia Lim is a physics undergraduate student at the University of Montreal. Recipient of one of the 2017 Trottier summer grants, she was supervised by iREx director René Doyon, iREx researcher Lison Malo and Canada-France-Hawaii Telescope resident astronomer Pascal Fouqué.
Her project was related to the infrared spectropolarimeter SPIRou. This instrument will search for Earth-size telluric planets in the habitable zone of nearby low-mass stars. The goal of her project is to participate in the final stages of the selection of candidate stars that SPIRou will probe by analyzing spectra of red dwarfs from the ESPaDOnS spectropolarimeter to find binaries, systems that should not be studied by SPIRou. Olivia also studied the magnetic field of low-mass stars that are candidates for the search of exoplanets.
My first project was on measuring the small-scale magnetic field of M dwarfs. We used high resolution intensity spectra from ESPaDOnS that we analyzed with a radiative transfer code.
My second project was on confirming et refuting binary and multiple systems made of at least one M dwarf using astrometric data from the GAIA and HIPPARCOS missions.
Magnetic fields in M dwarfs can hinder the detection of exoplanets by the radial velocity method. With the imminent delivery of SPIRou, whose primary mission is to detect and characterize telluric planets in orbit around low-mass stars, it is necessary to better understand the impact of magnetic fields on the data that will be collected by the instrument.
We know that approximately 50% of solar-type stars are part of a binary system. However, this ratio is not as accurately known for M-type stars. Yet, it is crucial to study binary and multiple systems for this spectral type since these systems should be avoided in the context of searching for exoplanets. Therefore it is important to have an updated and accurate catalog of binaries and multiples with M dwarfs.
The radiative transfer code used to measure the magnetic fields has certain limitations that must be quantified. This code uses parameters such as the temperature of the star and its gravity that have to be either adjusted, which requires more time, or fixed, which requires a good knowledge of the value of the parameters. In the second case, if a wrong value is given to the code, then the measured magnetic field can vary.
BD+74 456a is probably a giant! This star was classified in a triple system that was made of a K-type star, an M dwarf, and the giant star itself, but by analyzing its absolute magnitude and by comparing its parallax and proper motion to those of the other components in the system, we came to the conclusion that BD+74 456a is probably a background giant star that is not bound to the system.
I learned the different steps to reduce spectra: find the radial velocity of a star by cross-correlation with standards, correct a spectrum using this radial velocity, subtract telluric lines from a spectrum, etc.
I learned how to use astrometric data such as parallax, proper motion, separation and apparent magnitude to deduce the relative position of a pair of stars.
By comparing our results of measured magnetic fields to those obtained by other researchers, we could not see any correlation. However, we must be cautious with the conclusions that we draw from this: inconsistent results do not imply that one of the methods is completely incorrect. We have to make sure the methods really measure the same quantity and we must consider the errors in each method that could explain a divergence.
The catalogs used in the project on binaries and multiples was incomplete for the individual components of the systems. It was therefore impossible to directly compare astrometric measurements for these stars. We had to find alternative ways to deduce the relative position of the components of these systems to tell whether they are bound or not their system.
My favorite part of the project on magnetic fields was the fact that we could compare our results to those obtained by international researchers. This allowed us to put our method to the test, and we could also see that other people are also enthusiast about this subject and determined to find answers.
As for the project on binaries and multiples, I really enjoyed learning how to used astrometric data to compare the position of stars. The amount of information that can be extracted from only a few measurements has blown me away.
In terms of instrumentation, I had the opportunity to learn, at the Observatoire du Mont-Mégantic as well as at the Canada-France-Hawaii Telescope, how the data, the raw data actually, used by astronomers are collected! In my opinion, it is an aspect of astronomy that is different but just as interesting and complex as data analysis.