Spatial Distributions of Young Stars

TL;DR

This study examines the spatial distribution of young stars in Taurus-Auriga and Upper Sco, revealing their fractal structures, stellar velocity dispersions, and binary populations, using two-point correlation functions and power-law fits.

Contribution

It provides new measurements of fractal dimensions, velocity dispersions, and binary separation thresholds in young stellar associations, improving understanding of their spatial and dynamical properties.

Findings

Taurus has a fractal dimension of ~1.05, indicating filamentary structure.

Upper Sco's fractal dimension is possibly ~0.7, but with uncertainties.

Stellar motions have erased primordial structures on scales below 0.07° in Taurus and 1.7° in Upper Sco.

Abstract

We analyze the spatial distributions of young stars in Taurus-Auriga and Upper Sco as determined from the two-point correlation function (i.e. the mean surface density of neighbors). The corresponding power-law fits allow us to determine the fractal dimensions of each association's spatial distribution, measure the stellar velocity dispersions, and distinguish between the bound binary population and chance alignments of members. We find that the fractal dimension of Taurus is D~1.05, consistent with its filamentary structure. The fractal dimension of Upper Sco may be even shallower (D~0.7), but this fit is uncertain due to the limited area and possible spatially-variable incompleteness. We also find that random stellar motions have erased all primordial structure on scales of <0.07 degrees in Taurus and <1.7 degrees in Upper Sco; given ages of ~1 Myr and ~5 Myr, the corresponding internal velocity dispersions are ~0.2 km/s and ~1.0 km/s, respectively. Finally, we find that binaries can be distinguished from chance alignments at separations of <120" (17000 AU) in Taurus and 75" (11000 AU) in Upper Sco. The binary populations in these associations that we previously studied, spanning separations of 3-30", are dominated by binary systems. However, the few lowest-mass pairs (M_prim < 0.3 M_sun) might be chance alignments.