SACY
Search for Associations Containing Young Stars
The young moving groups or young associations are groups of stars that share similar 3D motion but are not necessarily spatially clustered on the sky, due to their proximity (typically <100 pc) and age (5-100 Myr). As Torres et al. (2008) highlighted, Orion at 50 pc would cover almost the entire sky. Their age and proximity also mean that they are no longer embedded in their natal cloud, not like spatially-clustered younger star-forming regions (Taurus, Orion), and they have drifted a significant difference from their original birth site. This drift distance is important for the identification of very wide binaries (see Elliot et al. 2016). All of these properties make them ideal for studies of multiplicity, disc evolution and searching for planets.
One problem of studying PMS multiple systems in their typical cradle environments (embedded clusters) is the lack of overlapping parameter space from sample to sample due to differing distances and extinction properties of the clusters that are generally studied. An alternative population of stars that can be used is the SACY sample (Search for Associations Containing Young stars), presented in Torres et al. (2008), and with very recent revised and updated solutions (Torres et al. in prep). This sample is a collection of ≈ 600 stars, <150 pc in distance, between the ages of 5-100 Myr, free of extinction. The members are extremely nearby and allow a very large orbital parameter space to be probed when combining different observational techniques (spectroscopy, interferometry, AO- and direct imaging) with little effect from N-body dynamics due to their youth.
A lot of work was done prior to my PhD on the SACY sample. The latest multiplicity studies identified the population of spectroscopic (<5 au) binaries (SB, Elliott et al. 2014), close (5-1000 au) visual binaries (Elliott et al. 2015), and wide and extremely wide (1000-100,000 au) binaries (Elliott et al. 2016a). In our last work (Zúñiga-Fernández et al. 2021), we updated the spectroscopic binary (SB) fraction of the SACY sample taking in consideration possible biases in our identification of SB candidates. We found that the three youngest associations (<30 Myr) have overall higher SB fractions (∼28%, sensitivity correction applied) compared with the five oldest associations (∼35−125 Myr) which are∼10% or lower. If the results on the SB fraction in the youngest associations were confirmed, it could hint at a non-universal multiplicity among SACY associations.
Figure 1. Left panel: Histogram of the photometric masses for targets in the SACY sample, estimated using the evolutionary models of Baraffe et al. 2015. Right panel: Histogram of the spectral types of targets in the SACY sample.
List of publications: SACY refereed publications (ADS library).
Future work on SACY:
Update database with information from lightcurves (TESS and K2).
Update binaries from SHINE survey.
Update binaries with Gaia EDR3 astrometry.
Create a repository and documentation for the database (web-based interface).