EWOCS-VIII: Internal kinematics and expansion of Westerlund 1 from VVVX proper motions

Authors:
Open Access
Publisher website
Google Scholar
Abstract
Context. Westerlund 1 (Wd1) is the most massive young star cluster known in the Milky Way and a key laboratory for studying the early dynamical evolution of massive clusters. Owing to its high extinction, the internal kinematics of its intermediate-mass stellar population remain largely unexplored. Aims. We aim to characterise the internal kinematic properties of Wd1 using a homogeneous census of near-infrared-selected cluster members and their proper motions (PMs). We considered PMs from the VIRAC2 catalogue, based on multi-epoch VVV/VVVX observations. Methods. For 1286 candidate members previously identified through near-IR photometry and astrometry (Paper I), we computed their PMs relative to the cluster mean motion and analysed them as a function of position and radius. We also investigated radial trends, tested the robustness of the results against the assumed cluster centre, and searched for preferred directions of motion. Results. We detected a statistically significant signature of expansion in the outer regions of Wd1, with the radial component of the relative PMs increasing with distance from the cluster centre. The expansion appears asymmetric, with the strongest gradient detected along a position angle PA= 84° ± 8° in the plane of the sky and with 5.9σ significance. We also found hints of inward radial motions in the central region, consistent with ongoing mass segregation, but only at a ≈2σ significance. Taken together, these results are consistent with a nearly monolithic formation scenario.
Funding Information
  • Fondo Nacional de Desarrollo Científico y Tecnológico (1230731)
  • ANID BASAL (FB210003)
  • ANID Millennium Science Initiative (ICN12_009)
  • ANID Millennium Science Initiative (AIM23-0001)
  • Fondo Nacional de Desarrollo Científico y Tecnológico (3260854)
  • Germany’s Excellence Strategy through the Cluster of Excellence ORIGINS (EXC–2094–39078331)
  • INAF Mini- Grant “Physical properties of Accreting young stellar objects: exploration of their light Curves and Emission
  • Fundação para a Ciência e a Tecnologia (2022.03809)
  • Fundação para a Ciência e a Tecnologia (UID/04434/2023)
  • International Space Science Institute (25-639)

This publication has 51 references indexed in Scilit: