Examinando por Autor "Dalessandro, Emanuele"

Mostrando 1 - 2 de 2
  • No hay miniatura disponible
    Ítem
    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.
  • No hay miniatura disponible
    Ítem
    The metallicity distribution in the core of the Sagittarus dwarf spheroidal: Minimising the metallicity biases
    (EDP Sciences, 2023-01) Minelli, Alice; Bellazzini, Michele; Mucciarelli, Alessio; Bonifacio, Piercarlo; Ibata, Rodrigo; Romano, Donatella; Monaco, Lorenzo; Caffau, Elisabetta; Dalessandro, Emanuele; Pascale, Raffaele
    We present the metallicity and radial velocity for 450 bona fide members of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy, measured from high-resolution spectra (R ' 18 000) obtained with FLAMES at the VLT. The targets were carefully selected (a) to sample the core of the main body of Sgr dSph while avoiding contamination from the central stellar nucleus, and (b) to prevent any bias on the metallicity distribution by selecting targets based on their Gaia parallax and proper motions. All the targets selected in this way were confirmed as radial velocity members. We used this sample to derive the first metallicity distribution of the core of Sgr dSph, which is virtually unaffected by metallicity biases. The observed distribution ranges from [Fe=H] ≃-2:3 to [Fe=H] ≃0:0, with a strong, symmetric, and relatively narrow peak around [Fe=H] ' -0:5 and a weak and extended metal-poor tail, in which only 13:8 ±1:9% of the stars have [Fe=H] < -1:0. We confirm previous evidence of correlations between chemical and kinematical properties of stars in the core of Sgr. In our sample, stars with [Fe=H] ≥ -0:6 display a lower velocity dispersion and a higher rotation amplitude than those with [Fe=H] < -0:6, confirming previous suggestions of disk/halo structure for the progenitor of the system. © The Authors 2023.