arXiv subjects

D. Massari

Publications and source records attributed to D. Massari.

77 records · Page 5Linked to original sources

arXiv2014

First evidence of fully spatially mixed first and second generations in globular clusters: the case of NGC 6362

We present the first evidence of multiple populations in the Galactic globular cluster NGC 6362. We used optical and near-UV Hubble Space Telescope and ground based photometry, finding that both the sub giant and red giant branches are split in two parallel sequences in all color magnitude diagrams where the F336W filter (or U band) is used. This cluster is one of the least massive globulars (M_tot~5x10^4 M_sun) where multiple populations have been detected so far. Even more interestingly and at odds with any previous finding, we observe that the two identified populations share the same radial distribution all over the cluster extension. NGC 6362 is the first system where stars from different populations are found to be completely spatially mixed. Based on N-body and hydrodynamical simulations of multiple stellar generations, we argue that, to reproduce these findings, NGC 6362 should have lost up to the 80% of its original mass

astro-ph.SR↗

arXiv2013

The Terzan 5 puzzle: discovery of a third, metal-poor component

We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex stellar system in the the Galactic bulge, known to have two populations at [Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide average [Fe/H]=-0.79 dex iron abundance and [alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity range of Terzan~5 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core collapse supernovae.

astro-ph.GA↗

arXiv2013

Double Blue Straggler sequences in GCs: the case of NGC 362

We used high-quality images acquired with the WFC3 on board the HST to probe the blue straggler star (BSS) population of the Galactic globular cluster NGC 362. We have found two distinct sequences of BSS: this is the second case, after M 30, where such a feature has been observed. Indeed the BSS location, their extension in magnitude and color and their radial distribution within the cluster nicely resemble those observed in M 30, thus suggesting that the same interpretative scenario can be applied: the red BSS sub-population is generated by mass transfer binaries, the blue one by collisions. The discovery of four new W UMa stars, three of which lying along the red-BSS sequence, further supports this scenario. We also found that the inner portion of the density profile deviates from a King model and is well reproduced by either a mild power-law (α-0.2) or a double King profile. This feature supports the hypothesis that the cluster is currently undergoing the core collapse phase. Moreover, the BSS radial distribution shows a central peak and monotonically decreases outward without any evidence of an external rising branch. This evidence is a further indication of the advanced dynamical age of NGC 362: in fact, together with M 30, NGC 362 belongs to the family of dynamically old clusters (Family III) in the "dynamical clock" classification proposed by Ferraro et al. (2012). The observational evidence presented here strengthens the possible connection between the existence of a double BSS sequence and a quite advanced dynamical status of the parent cluster.

astro-ph.SR↗

arXiv2013

The velocity dispersion profile of NGC 6388 from resolved-star spectroscopy: no evidence of a central cusp and new constraints on the black hole mass

By combining high spatial resolution and wide-field spectroscopy performed, respectively, with SINFONI and FLAMES at the ESO/VLT we measured the radial velocities of more than 600 stars in the direction of NGC 6388, a Galactic globular cluster which is suspected to host an intermediate-mass black hole. Approximately 55% of the observed targets turned out to be cluster members. The cluster velocity dispersion has been derived from the radial velocity of individual stars: 52 measurements in the innermost 2", and 276 stars located between 18" and 600". The velocity dispersion profile shows a central value of ~13 km/s, a flat behavior out to ~60" and a decreasing trend outwards. The comparison with spherical and isotropic models shows that the observed density and velocity dispersion profiles are inconsistent with the presence of a central black hole more massive than ~2000 Msol. These findings are at odds with recent results obtained from integrated light spectra, showing a velocity dispersion profile with a steep central cusp of 23-25 km/s at r<2" and suggesting the presence of a black hole with a mass of 17,000 Msol (Lutzgendorf et al. 2011). We also found some evidence of systemic rotation with amplitude Arot ~8 km/s in the innermost 2" (0.13 pc), decreasing to Arot= 3.2 km/s at 18"<r<160".

astro-ph.SR↗

arXiv2013

Terzan 5: a Fossil Remnant of the Galactic Bulge

Terzan 5 is a stellar system located in the Galactic Bulge, at a distance of 5.9 kpc. Recent discoveries show that it hosts two stellar populations with different iron abundance (Δ[Fe/H]=0.5). Such a large difference has been measured only in ω Centauri in the Galactic halo. Moreover no anticorrelation is observed in Terzan 5, hence it is not a genuine globular cluster. The observed chemical patterns are strikingly similar to those observed in the Bulge stars. This suggests that Terzan 5 is a remnant fragment of the Galactic bulge.

astro-ph.GA↗