The globular cluster VVV CL002 falling down to the hazardous Galactic centre

© 2024 The Author(s). Published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Context. The Galactic centre is hazardous for stellar clusters because of the strong tidal force in action there. It is believed that many clusters were destroyed there and contributed stars to the crowded stellar field of the bulge and the nuclear stellar cluster. However, the development of a realistic model to predict the long-term evolution of the complex inner Galaxy has proven difficult, and observations of surviving clusters in the central region would provide crucial insights into destruction processes. Aims: Among the known Galactic globular clusters, VVV CL002 is the closest to the centre, at 0.4 kpc, but has a very high transverse velocity of 400 km s−1. The nature of this cluster and its impact on Galactic astronomy need to be addressed with spectroscopic follow up. Methods: Here we report the first measurements of its radial velocity and chemical abundance based on near-infrared high-resolution spectroscopy. Results: We find that this cluster has a counter-rotating orbit constrained within 1.0 kpc of the centre, and as close as 0.2 kpc at the perigalacticon, confirming that the cluster is not a passerby from the halo but a genuine survivor enduring the harsh conditions of the tidal forces of the Galactic mill. In addition, its metallicity and α abundance ([α/Fe] ≃ +0.4 and [Fe/H] = −0.54) are similar to those of some globular clusters in the bulge. Recent studies suggest that stars with such α-enhanced stars were more common at 3-6 kpc from the centre around 10 Gyr ago. Conclusions: We infer that VVV CL002 was formed outside but is currently falling down to the centre, showcasing a real-time event that must have occurred to many clusters a long time ago.Peer reviewe

The Influence of Experience on Gazing Patterns during Endovascular Treatment: Eye-Tracking Study

Objective: In various fields, differences in eye-gazing patterns during tasks between experts and novices have been evaluated. The aim of this study was to investigate gazing patterns during neuro-endovascular treatment using an eye-tracking device and assess whether gazing patterns depend on the physician’s experience or skill. Methods: Seven physicians performed coil embolization for a cerebral aneurysm in a silicone vessel model under biplane X-ray fluoroscopy, and their gazing patterns were recorded using an eye-tracking device. The subjects were divided into three groups according to experience, highly experienced (Expert) group, intermediately experienced (Trainee) group, and less experienced (Novice) group. The duration of fixation on the anterior–posterior (AP) view screen, lateral (LR) view, and out-of-screen were compared between each group. Results: During microcatheter navigation, the Expert and Trainee groups spent a long time on fixation to AP, while the Novice group split their attention between each location. In coil insertion, the Expert group gazed at both the AP and the LR views with more saccades between screens. In contrast, the Trainee group spent most of their time only on the AP view screen and the Novice group spent longer out-of-screen. Conclusion: An eye-tracking device can detect different gazing patterns among physicians with several experiences and skill levels of neuroendovascular treatment. Learning the gazing patterns of experts using eye tracking may be a good educational tool for novices and trainees

Metallicities of Classical Cepheids in the Inner Galactic Disk

Metallicity gradients refer to the sloped radial profiles of the metallicities of gas and stars and are commonly seen in disk galaxies. A well-defined metallicity gradient of the Galactic disk is observed particularly well with classical Cepheids, which are good stellar tracers thanks to their period–luminosity relation, allowing precise distance estimation and other advantages. However, the measurement of the inner-disk gradient has been impeded by the incompleteness of previous samples of Cepheids and the limitations of optical spectroscopy in observing highly reddened objects. Here we report the metallicities of 16 Cepheids measured with high-resolution spectra in the near-infrared YJ bands. These Cepheids are located at 3–5.6 kpc in Galactocentric distance, R _GC , and reveal the metallicity gradient in this range for the first time. Their metallicities are mostly between 0.1 and 0.3 dex in [Fe/H] and more or less follow the extrapolation of the metallicity gradient found in the outer part, R _GC > 6.5 kpc. The gradient in the inner disk may be shallower or even flat, but the small sample does not allow the determination of the slope precisely. More extensive spectroscopic observations would also be necessary for studying minor populations, if any, with higher or lower metallicities that were reported in previous literature. In addition, the 3D velocities of our inner-disk Cepheids show a kinematic pattern that indicates noncircular orbits caused by the Galactic bar, which is consistent with the patterns reported in recent studies on high-mass star-forming regions and red giant branch stars