Examinando por Autor "Dalessandro E."

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    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).
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    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.