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1. The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIV. Differences in Internal Kinematics of Multiple Stellar Populations

   https://doi.org/10.3847/1538-4357/acaec6  

   Libralato, Mattia ; Vesperini, Enrico ; Bellini, Andrea ; Milone, Antonino P. ; van der Marel, Roeland P. ; Piotto, Giampaolo ; Anderson, Jay ; Aparicio, Antonio ; Barbuy, Beatriz ; Bedin, Luigi R. ; et al ( February 2023 , The Astrophysical Journal)

   Abstract Our understanding of the kinematic properties of multiple stellar populations (mPOPs) in Galactic globular clusters (GCs) is still limited compared to what we know about their chemical and photometric characteristics. Such limitation arises from the lack of a comprehensive observational investigation of this topic. Here we present the first homogeneous kinematic analysis of mPOPs in 56 GCs based on high-precision proper motions computed with Hubble Space Telescope data. We focused on red-giant-branch stars, for which the mPOP tagging is clearer, and measured the velocity dispersion of stars belonging to first (1G) and second generations (2G). We find that 1G stars are generally kinematically isotropic even at the half-light radius, whereas 2G stars are isotropic at the center and become radially anisotropic before the half-light radius. The radial anisotropy is induced by a lower tangential velocity dispersion of 2G stars with respect to the 1G population, while the radial component of the motion is comparable. We also show possible evidence that the kinematic properties of mPOPs are affected by the Galactic tidal field, corroborating previous observational and theoretical results suggesting a relation between the strength of the external tidal field and some properties of mPOPs. Although limited to the GCs’more »central regions, our analysis leads to new insights into the mPOP phenomenon, and provides the motivation for future observational studies of the internal kinematics of mPOPs.« less
2. Blanco DECam Bulge Survey (BDBS). VII. Multiple Populations in Globular Clusters of the Galactic Bulge

   https://doi.org/10.3847/1538-4357/ac94c5  

   Kader, Justin A. ; Pilachowski, Catherine A. ; Johnson, Christian I. ; Rich, R. Michael ; Young, Michael D. ; Simion, Iulia T. ; Clarkson, William I. ; Michael, Scott ; Kunder, Andrea ; Vivas, Anna Katherina ; et al ( November 2022 , The Astrophysical Journal)

   Abstract We present photometric evidence for multiple stellar populations (MPs) in 14 globular clusters (GCs) toward the southern Galactic bulge. The photometric data come as part of the Blanco DECam Bulge Survey, which is a deep, wide-field near-UV-near-IR ( ugriz Y) survey of the southern Galactic bulge. Here, we present the first systematic study of bulge GC multiple populations with deep photometry including the u band, which is a crucial indicator of the abundance of CNO-bearing molecules in stellar atmospheres. We identify cluster members using Gaia EDR3 proper motion measurements, and then isolate red giant branch stars using r versus u − r color–magnitude diagrams. We find evidence suggesting all 14 clusters host at least two populations, and NGC 6441, NGC 6626, and NGC 6656 appear to have at least three populations. Many of these clusters are not part of the Hubble Space Telescope (HST) surveys nor do they have comprehensive spectroscopic analyses so we are presenting the first evidence of MPs in several clusters. Not only do we find a strong anticorrelation between the fraction of first-generation stars and cluster absolute V magnitude, but the correlation coefficient and cluster-to-cluster scatter are similar to the results obtained from HST. Ourmore »ground-based data extend to much larger radial distances than similar HST observations, enabling a reliable estimate of the global fraction of first-generation stars in each cluster. This study demonstrates that ground-based u -band photometry as provided by DECam will prove powerful in the study of multiple populations in resolved GCs.« less
3. 3D core kinematics of NGC 6362: central rotation in a dynamically evolved globular cluster

   https://doi.org/10.1093/mnras/stab1257  

   Dalessandro, Emanuele ; Raso, Silvia ; Kamann, Sebastian ; Bellazzini, Michele ; Vesperini, Enrico ; Bellini, Andrea ; Beccari, Giacomo ( July 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present a detailed 3D kinematic analysis of the central regions (R < 30 arcsec) of the low mass and dynamically evolved galactic globular cluster (GC) NGC 6362. The study is based on data obtained with ESO-VLT/MUSE used in combination with the adaptive optics module and providing ∼3000 line-of-sight radial velocities, which have been complemented with Hubble Space Telescope proper motions. The quality of the data and the number of available radial velocities allowed us to detect for the first time a significant rotation signal along the line of sight in the cluster core with amplitude of ∼1 km s−1 and with a peak located at only ∼20 arcsec from the cluster centre, corresponding to only ${\sim}10{{\ \rm per\ cent}}$ of the cluster half-light radius. This result is further supported by the detection of a central and significant tangential anisotropy in the cluster innermost regions. This is one of the most central rotation signals ever observed in a GC to date. We also explore the rotational properties of the multiple populations hosted by this cluster and find that Na-rich stars rotate about two times more rapidly than the Na-poor sub-population thus suggesting that the interpretation of the present-day GC properties requiremore »a multicomponent chemo-dynamical approach. Both the rotation amplitude and peak position would fit qualitatively the theoretical expectations for a system that lost a significant fraction of its original mass because of the long-term dynamical evolution and interaction with the Galaxy. However, to match the observations more quantitatively further theoretical studies to explore the initial dynamical properties of the cluster are needed.« less
4. Evidence for C and Mg variations in the GD-1 stellar stream

   https://doi.org/10.1093/mnras/stac1953  

   Balbinot, Eduardo ; Cabrera-Ziri, Ivan ; Lardo, Carmela ( July 2022 , Monthly Notices of the Royal Astronomical Society)

   Dynamically cold stellar streams are the relics left over from globular cluster dissolution. These relics offer a unique insight into a now fully disrupted population of ancient clusters in our Galaxy. Using a combination of Gaia eDR3 proper motions, optical and near-UV colours, we select a sample of likely Red Giant Branch stars from the GD-1 stream for medium-low resolution spectroscopic follow-up. Based on radial velocity and metallicity, we are able to find 14 new members of GD-1, 5 of which are associated with the spur and blob/cocoon off-stream features. We measured C-abundances to probe for abundance variations known to exist in globular clusters. These variations are expected to manifest in a subtle way in globular clusters with such low masses ($\sim 10^4\,{\rm ~\textrm {M}_\odot }$) and metallicities ([Fe/H] ∼ −2.1 dex). We find that the C-abundances of the stars in our sample display a small but significant (3σ level) spread. Furthermore, we find ∼3σ variation in Mg-abundances among the stars in our sample that have been observed by APOGEE. These abundance patterns match the ones found in Galactic globular clusters of similar metallicity. Our results suggest that GD-1 represents another fully disrupted low-mass globular cluster where light-element abundance spreadsmore »have been found.

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5. HST proper motions on the far side of the Galactic bar—data

   https://doi.org/10.1093/mnras/stad1911  

   Soto, Mario ; Kuijken, Konrad ; Rich, R. Michael ; Clarkson, William I. ; Nilo Castellón, José Luis ; Fernández-Trincado, José G. ; Contreras Ramos, Rodrigo ; Kunder, Andrea ; Baravalle, Laura D. ; Alonso, M. Victoria ; et al ( June 2023 , Monthly Notices of the Royal Astronomical Society)

   This is the third paper in a series that attempts to observe a clear signature of the Galactic bar/bulge using kinematic observations of the bulge stellar populations in low foreground extinction windows. We report on the detection of ∼100 000 new proper motions in four fields covering the far side of the Galactic bar/bulge, at negative longitudes. Our proper motions have been obtained using observations from the Advance Camera for Surveys (ACS), on board of the Hubble Space Telescope (HST), with a time-baseline of 8–9 years, which has produced accuracies better than 0.5 mas yr−1 for a significant fraction of the stellar populations with F814W < 23 mag. Interestingly, as shown in previous works, the Hess diagrams show a strikingly similar proper motion distribution to fields closer to the Galactic center and consistent with an old stellar population. The observed kinematics point to a significant bulge rotation, which seems to predominate even in fields as far as l ≃ −8°, and is also reflected in the changes of the velocity ellipsoid in the l, b plane as a function of distance.