Stellar Spins in the Open Cluster NGC 2516

Brian F. Healy, P. R. McCullough

Published 2020-09-29Version 1

Measuring the distribution of stellar spin axis orientations in a coeval group of stars probes the physical processes underlying the stars' formation. In this paper, we use spectro-photometric observations of the open cluster NGC 2516 to determine the degree of spin alignment among its stars. We combine $\textit{TESS}$ light curves, ground-based spectroscopy from the Gaia-ESO and GALAH surveys, broad-band stellar magnitudes from several surveys, and $\textit{Gaia}$ astrometry to measure 33 stellar inclinations and quantify overall cluster rotation. Our measurements suggest that stellar spins in this cluster are isotropically oriented, while allowing for the possibility that they are moderately aligned. An isotropic distribution of NGC 2516 spins would imply a star-forming environment in which turbulence dominated ordered motion, while a moderately aligned distribution would suggest a more substantial contribution from rotation. We also perform a three-dimensional analysis of the cluster's internal kinematics, finding no significant signatures of overall rotation. Stemming from this analysis, we identify evidence of cluster contraction, suggesting possible ongoing mass segregation in NGC 2516.