Examinando por Autor "Mateo, Mario"

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    Fast rotating blue stragglers prefer loose clusters
    (Nature Research, 2023-12) Ferraro, Francesco R.; Mucciarelli, Alessio; Lanzoni, Barbara; Pallanca, Cristina; Cadelano, Mario; Billi, Alex; Sills, Alison; Vesperini, Enrico; Dalessandro, Emanuele; Beccari, Giacomo; Monaco, Lorenzo; Mateo, Mario
    Blue stragglers are anomalously luminous core hydrogen-burning stars formed through mass-transfer in binary/triple systems and stellar collisions. Their physical and evolutionary properties are largely unknown and unconstrained. Here we analyze 320 high-resolution spectra of blue stragglers collected in eight galactic globular clusters with different structural characteristics and show evidence that the fraction of fast rotating blue stragglers (with rotational velocities larger than 40 km/s) increases for decreasing central density of the host system. This trend suggests that fast spinning blue stragglers prefer low-density environments and promises to open an unexplored route towards understanding the evolutionary processes of these stars. Since large rotation rates are expected in the early stages of both formation channels, our results provide direct evidence for recent blue straggler formation activity in low-density environments and put strong constraints on the timescale of the collisional blue straggler slow-down processes.
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    Fast-rotating Blue Straggler Stars in the Globular Cluster NGC 3201
    (Institute of Physics, 2023-10-01) Billi, Alex; Ferraro, Francesco R.; Mucciarelli, Alessio; Lanzoni, Barbara; Cadelano, Mario; Monaco, Lorenzo; Mateo, Mario; Bailey, John I.; Reiter, Megan; Olszewski, Edward W.
    We used high-resolution spectra acquired with the Magellan Telescope to measure radial and rotational velocities of approximately 200 stars in the Galactic globular cluster NGC 3201. The surveyed sample includes blue straggler stars (BSSs) and reference stars in different evolutionary stages (main-sequence turnoff, subgiant, red giant, and asymptotic giant branches). The average radial velocity value (〈V r 〉 = 494.5 ± 0.5 km s−1) confirms a large systemic velocity for this cluster and was used to distinguish 33 residual field interlopers. The final sample of member stars has 67 BSSs and 114 reference stars. Similarly to what is found in other clusters, the totality of the reference stars has negligible rotation (< 20 km s−1), while the BSS rotational velocity distribution shows a long tail extending up to ∼200 km s−1, with 19 BSSs (out of 67) spinning faster than 40 km s−1. This sets the percentage of fast-rotating BSSs to ∼28%. Such a percentage is roughly comparable to that measured in other loose systems (ω Centauri, M4, and M55) and significantly larger than that measured in high-density clusters (as 47 Tucanae, NGC 6397, NGC 6752, and M30). This evidence supports a scenario where recent BSS formation (mainly from the evolution of binary systems) is occurring in low-density environments. We also find that the BSS rotational velocity tends to decrease for decreasing luminosity and surface temperature, similarly to what is observed in main-sequence stars. Hence, further investigations are needed to understand the impact of BSS internal structure on the observed rotational velocities. © 2023. The Author(s). Published by the American Astronomical Society.