The role of rotation on the formation of second generation stars in globular clusters

Abstract

By means of 3D hydrodynamic simulations, we explore the effects of rotation in the formation of second-generation (SG) stars in globular clusters (GC). Our simulations follow the SG formation in a first-generation (FG) internally rotating GC; SG stars form out of FG asymptotic giant branch (AGB) ejecta and external pristine gas accreted by the system. We have explored two different initial rotational velocity profiles for the FG cluster and two different inclinations of the rotational axis with respect to the direction of motion of the external infalling gas, whose density has also been varied. For a low (10−24g cm−3) external gas density, a disk of SG helium-enhanced stars is formed. The SG is characterized by distinct chemo-dynamical phase space patterns: it shows a more rapid rotation than the FG with the helium-enhanced SG subsystem rotating more rapidly than the moderate helium-enhanced one. In models with high external gas density (10−23g cm−3), the inner SG disc is disrupted by the early arrival of external gas and only a small fraction of highly enhanced helium stars preserves the rotation acquired at birth. Variations in the inclination angle between the rotation axis and the direction of the infalling gas and the velocity profile can slightly alter the extent of the stellar disc and the rotational amplitude. The results of our simulations illustrate the complex link between dynamical and chemical properties of multiple populations and provide new elements for the interpretation of observational studies and future investigations of the dynamics of multiple-population GCs.

The HST Large Programme on NGC 6752 ‐ V. Differences in luminosity and mass function among stellar populations

“…In particular, a number of theoretical studies of the formation of multiple populations (see, e.g. Bekki 2010, 2011; Calura et al 2019; D'Ercole et al 2008; Lacchin et al 2022) predict that 2P stars formed more centrally concentrated than 1P stars and may be characterized by kinematic differences, which are either imprinted at the time of the cluster's formation (see e.g. Bekki 2010, 2011; Hénault‐Brunet et al 2015; Lacchin et al 2022) and/or produced during the cluster's evolution (see e.g.…”

The structural properties of multiple populations in the dynamically young globular cluster NGC 2419

“…The kinematical and structural properties of MPs can provide important insights into the early epochs of GC formation and evolution. One of the predictions of MP formation models (see e.g., D'Ercole et al 2008;Calura et al 2019) is that SP stars form a centrally segregated subsystem possibly characterised by a more rapid internal rotation (Bekki 2011;Lacchin et al 2022) than the more spatially extended FP system. Although the original structural and kinematical differences between FP and SP stars are gradually erased during the long-term dynamical evolution of GCs (see e.g., Vesperini et al 2013;Hénault-Brunet et al 2015;Miholics et al 2015), some clusters are expected to retain some memory of their primordial properties.…”