Examinando por Autor "Cadelano M."
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Ítem Radial variation of the stellar mass functions in the globular clusters M15 and M30: Clues of a non-standard IMF?(Oxford University Press, 2020-12) Cadelano M.; Dalessandro E.; Webb J.J.; Vesperini E.; Lattanzio D.; Beccari G.; Gomez M.; Monaco L.We exploit a combination of high-resolution Hubble Space Telescope and wide-field ESO-VLT observations to study the slope of the global mass function (αG) and its radial variation (α(r)) in the two dense, massive and post core-collapse globular clusters M15 and M30. The available data set samples the clusters' main sequence down to ∼0.2 M⊙ and the photometric completeness allows the study of the mass function between 0.40 M⊙ and 0.75 M⊙ from the central regions out to their tidal radii. We find that both clusters show a very similar variation in α(r) as a function of clustercentric distance. They both exhibit a very steep variation in α(r) in the central regions, which then attains almost constant values in the outskirts. Such a behaviour can be interpreted as the result of long-term dynamical evolution of the systems driven by mass-segregation and mass-loss processes. We compare these results with a set of direct N-body simulations and find that they are only able to reproduce the observed values of α(r) and αG at dynamical ages (t/trh) significantly larger than those derived from the observed properties of both clusters. We investigate possible physical mechanisms responsible for such a discrepancy and argue that both clusters might be born with a non-standard (flatter/bottom-lighter) initial mass function. © 2020 The Author(s).Ítem Rotational velocities of blue straggler stars in the globular cluster M 55(EDP Sciences, 2024-10) Billi A.; Ferraro F.R.; Mucciarelli A.; Lanzoni B.; Cadelano M.; Monaco L.By using high-resolution spectra acquired with FLAMES-GIRAFFE at the ESO/VLT, we measured the radial and rotational velocities of 115 stars in the Galactic globular cluster M 55. After field decontamination based on the radial velocity values, the final sample of member stars is composed of 32 blue straggler stars (BSSs) and 76 reference stars populating the red giant and horizontal branches of the cluster. In agreement with previous findings, the totality of red giant branch stars has negligible rotation (<10 km s-1) and horizontal branch stars have rotational velocities of 40 km s-1 at most. In contrast, the BSS rotational velocity distribution shows a long tail extending up to ~200 km s-1, with 15 BSSs (out of 32), spinning faster than 40 km s-1. By defining the threshold for fast rotating BSSs at 40 km s-1, this sets the percentage of these stars at 47 ±14%. Such a large value has never been found before in any globular clusters. It is roughly comparable to that measured in other loose systems (ω Centauri, M 4, and NGC 3201) and significantly larger than that observed in high-density clusters (as 47 Tucanae, NGC 6397, NGC 6752, and M 30). This evidence supports a scenario whereby recent BSS formation is occurring in low-density environments. We also find that the BSS rotational velocity tends to decrease for decreasing luminosity, as found for another loose cluster of the sample, namely, NGC 3201. © The Authors 2024.Ítem The bulge globular cluster Terzan 6 as seen from multi-conjugate adaptive optics and HST(EDP Sciences, 2025-03) Loriga M.; Pallanca C.; Ferraro F.R.; Dalessandro E.; Lanzoni B.; Cadelano M.; Origlia L.; Fanelli C.; Geisler D.; Villanova S.This work consists of the first detailed photometric study of Terzan 6, one of the least known globular clusters in the Galactic bulge. Through the analysis of high angular resolution and multiwavelength data obtained from adaptive optics corrected and space observations, we built deep, optical and near-infrared color-magnitude diagrams reaching ≈4 magnitudes below the main-sequence turnoff. Taking advantage of four different epochs of observations, we measured precise relative proper motions for a large sample of stars, from which cluster members have been solidly distinguished from Galactic field interlopers. A noncanonical reddening law (with RV = 2.85) and high-resolution differential reddening map, with color excess variations up to δE(B-V) ≈0.8 mag, have been derived in the direction of the system. According to these findings, new values for the extinction and distance modulus have been obtained: E(B-V) = 2.36 ± 0.05 and (m-M)0 = 14.46 ± 0.10 (corresponding to d = 7.8 ± 0.3 kpc), respectively. We also provide the first determinations of the cluster center and projected density profile from resolved star counts. The center is offset by more than 7″ to the east from the literature value, and the structural parameters obtained from the King model fitting to the density profile indicate that Terzan 6 is in an advanced stage of its dynamical evolution, with a large value for the concentration parameter (c = 1.94-0.26+0.24) and a small core radius (rc = 2.6-0.7+0.09 arcsec). We also determined the absolute age of the system, finding t = 13 ± 1 Gyr, in agreement with the old ages found for the globular clusters in the Galactic bulge. From the redetermination of the absolute magnitude of the red giant branch bump and the recent estimate of the cluster global metallicity, we find that Terzan 6 nicely matches the tight relation between these two parameters drawn by the Galactic globular cluster population. © 2025 The Authors.