G. Ettorre | Searcharxiv

arXiv2026

Right round: onset and long-term evolution of rotation in star clusters

We present the results of a detailed kinematic analysis of a significant fraction of the known population of Galactic star clusters aimed at constraining the physical mechanisms driving the onset and evolution of cluster rotation. Our study reveals for the very first time the presence of rotation in clusters at any age, with about $25\%-30\%$ of systems in the sample showing significant evidence of rotation. This result increases by a factor of $\sim5$ the number of clusters identified as rotators so far and it finally enables an observational reading of cluster rotation as a function of time. Young ($<500$ Myr) clusters show a larger range of rotation velocities than older systems. In addition, at young ages we observe a significantly larger fraction ($50\%-60\%$) of rotating systems than at older ones ($\sim 15\%$). These purely empirical results are compatible with rotation being imprinted during the very early stages of cluster formation and early evolution and then being progressively erased by the long-term effects of dynamical evolution. For the sub-sample of clusters for which we were able to perform a full 3D analysis, we calculated the angle between the internal rotation axis and that of the cluster orbital motion. Interestingly, while for clusters with an age smaller than their orbital period we observe similar fractions of prograde and retrograde systems, more evolved clusters appear to be preferentially prograde. We argue that such a behavior is in qualitative agreement with the expectations for the evolution of systems in which primordial rotation was imprinted by the parent molecular cloud and/or by the following hierarchical cluster assembly processes, and in which internal cluster dynamics and interactions with the Galactic field have induced a torque-driven alignment between cluster rotation and orbital motion.

astro-ph.GA↗

arXiv2025

PARSEC V2.0: Rotating tracks and isochrones for seven addtional metallicities in the range Z=0.0001-0.03

PARSEC v2.0 rotating stellar tracks were previously presented for six values of metallicity from subsolar to solar values, with initial rotation rates ($ω_\mathrm{i}$, defined as the ratio of angular velocity and its critical value) spanning from the non-rotating case to very near the critical velocity (i.e. $ω_\mathrm{i}=0.99$), and for initial masses covering the $\sim 0.7 M_\odot$ to $14 M_\odot$ interval. Furthermore, we provided the corresponding isochrones converted into several photometric systems, for different inclination angles between the line-of-sight and the rotation axes, from $0^\circ$ (pole-on) to $90^\circ$ (equator-on). In this work, we expand this database with seven other sets of metallicity, including five sets of low metallicity ($Z=0.0001-0.002$) and two sets of super-solar values (up to $Z=0.03$). Here, we present the new stellar tracks, comprising $\sim$3\,040 tracks in total ($\sim$5\,500 including previous sets), along with the new corresponding rotating isochrones. We also introduce the possibility of creating isochrones, by interpolation, for values of rotating rates not available in the initial set of tracks. We compare a selection of our new models with rotating stellar tracks from the Geneva Stellar Evolution Code, and we assess the quality of our new tracks by fitting the colour-magnitude diagram of the open cluster NGC6067. We take advantage of the projected rotational velocity of member stars measured by Gaia to validate our results and examine the surface oxygen abundances in comparison with the observed data. All newly computed stellar tracks and isochrones are retrievable via our dedicated web databases and interfaces.

astro-ph.SR↗