Research Byte

Published in the RSAA Lunations
Vol1 Issue20 1–30 September 2021

Finding young and adolescent stars with Gaia and the ANU 2.3m telescope

Understanding the origin of young stars is associated with big questions of stellar astrophysics, exoplanet formation and evolution, and the structure of the Galaxy.  It was a major component of the research of prior Mt Stromlo directors Olin J. Eggen and Bart J. Bok, who were primarily able to study associations of the most massive blue stars of O and B spectral type. For more solar-type stars, the youngest can be found through X-ray and infrared surveys, but after approximately a 10 Myr age, the only way to conclusively determine in the past that stars were young was through medium to high resolution spectroscopy, which can be time-consuming for large samples spread over the whole sky.

The launch of the Gaia satellite in principle changed the game, by knowing the distance to many more individual stars directly, and therefore being able to determine if their radii were inflated due to still radiating away their formation energy. This sort of data had never been used for a larger stellar sample before however, so it was important to carefully determine how useful this space mission data could be, and whether both known unknown and unknown unknown interlopers would dominate. 

We observed 756 potential young stars selected due to over luminosity (see figure) with both the Echelle and the WiFeS instruments using the ANU 2.3m telescope. We found spectroscopic signs of youth in 346 of these stars - either Lithium which was not yet burnt deep in the convective layers, or an over-active corona showing Calcium or Hydrogen emission. This was the largest single spectroscopic sample of nearby young stars found at once (with second place also going previous work using the ANU 2.3m, and third place going to a 2dF survey). After making a post facto selection of stars after excluding potential astrometric binaries and high reddening stars, 80% of the remaining sample had spectroscopic signs of youth. 

The impact of this research is that now we know how to find groups of young stars using data from publicly available data form the Gaia and WISE missions alone. This means that that we will soon be able to map not only how stars are currently forming, but also how stars formed over the past few hundred million years, some of which became long lived clusters with the rest gradually dispersing throughout the Galactic disc. 

Further information can be found at:

https://ui.adsabs.harvard.edu/abs/2021MNRAS.503..938Z/abstract

The group’s future work will combine the Chronostar code that determines ages of stellar association with related techniques from our collaborators in Austin, Texas:

https://ui.adsabs.harvard.edu/abs/2019MNRAS.489.3625C/abstract

https://ui.adsabs.harvard.edu/abs/2021ApJ...917...23K/abstract 

 

Michael Ireland, Marusa Zerjal and Adam Rains.