Chemical and kinematical properties of BSSs and HB stars in NGC 6397

Abstract

We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 Blue Straggler Stars (BSSs) and 86 main sequence turn-off and sub-giant branch stars in the nearby globular cluster NGC 6397. We measured rotational velocities and Fe, O and Mg abundances. All the unevolved stars in our sample turn out to have low rotational velocites (v sin i< 10\kms), while HB stars and BSSs show a broad distribution, with values ranging from 0 to 70 \kms. For HB stars with T<10500 K there is a clear temperature-oxygen anti-correlation, that can be understood if the star position along the HB is mainly determined by the He content. The hottest BSSs and HB stars (with temperatures T>8200 K and T> 10500 K, respectively) also show significant deviations in their iron abundance with respect to the cluster metallicity (as traced by the unevolved stars, [Fe/H]=-2.12). While similar chemical patterns have been already observed in other hot HB stars, this is the first evidence ever collected for BSSs. We interprete these abundance anomalies as due to the metal radiative levitation, occurring in stars with shallow or no convective envelopes.

References in corpus (6)

• Looking outside the Galaxy: the discovery of chemical anomalies in 3 old Large Magellanic Cloud clusters
• Discovery of Carbon/Oxygen depleted Blue Straggler Stars in 47 Tucanae: the chemical signature of a mass-transfer formation process
• Chemical composition of A and F dwarf members of the Coma Berenices open cluster
• Chemical composition of A and F dwarfs members of the Pleiades open cluster
• Atomic diffusion and mixing in old stars II. Observations of stars in the globular cluster NGC 6397 with VLT/FLAMES-GIRAFFE
• Absolute motions of globular clusters. II. [HST astrometry and VLT radial velocities in NGC6397]

Cited by in corpus (40)

• Multiple Stellar Populations in Globular Clusters
• N-body modeling of globular clusters: Masses, mass-to-light ratios and intermediate-mass black holes
• Helium enhanced stars and multiple populations along the horizontal branch of NGC2808: direct spectroscopic measurements
• The SUMO project I. A survey of multiple populations in globular clusters
• MUSE crowded field 3D spectroscopy of over 12,000 stars in the globular cluster NGC 6397 - I. The first comprehensive spectroscopic HRD of a globular cluster
• Global and non-global parameters of horizontal branch morphology of globular clusters
• Detailed abundance analysis from integrated high-dispersion spectroscopy: Globular clusters in the Fornax Dwarf Spheroidal
• A stellar-mass black hole population in the globular cluster NGC 6101?
• Hubble Space Telescope proper motion (HSTPROMO) catalogs of Galactic globular clusters. III. Dynamical distances and mass-to-light ratios
• Helium and Multiple Populations in the Massive Globular Cluster NGC6266 (M62)
• Does NGC 6397 contain an intermediate-mass black hole or a more diffuse inner subcluster?
• Spectrum Syntheses of High Resolution Integrated Light Spectra of Galactic Globular Clusters
• Horizontal-branch morphology and multiple stellar populations in the anomalous globular cluster M22
• The Na-O anticorrelation in horizontal branch stars. V. NGC 6723
• FLAMES and XSHOOTER spectroscopy along the two BSS sequences of M30
• Fast rotating Blue Stragglers prefer loose clusters
• The helium abundance in the metal-poor globular clusters M30 and NGC6397
• The Na-O anticorrelation in horizontal branch stars. IV. M22
• New clues on the nature of the companion to PSR~J1740-5340 in NGC6397 from XSHOOTER spectroscopy
• NGC 5694: another foster son of the Galactic Halo
• The R-Process Alliance: Discovery of a low-alpha, r-Process-Enhanced Metal-Poor Star in the Galactic Halo
• Blue straggler masses from pulsation properties. II. Topology of the Instability Strip
• Spinning like a Blue Straggler: the population of fast rotating Blue Straggler stars in Omega Centauri
• Optimal Integrated Abundances for Chemical Tagging of Extragalactic Globular Clusters
• Barium Surface Abundances of Blue Stragglers in the Open Cluster NGC 6819
• Model computations of blue stragglers and W UMa-type stars in globular clusters
• Another brick in understanding chemical and kinematical properties of BSSs: NGC 6752
• Blue Straggler Star Populations in Globular Clusters: I. Dynamical Properties of Blue Straggler Stars in NGC 3201, NGC 6218 and $\omega$ Centauri
• Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)
• Absence of obvious tidal tails around the globular cluster NGC 6397
• Blue Straggler Stars in Globular Clusters: a powerful tool to probe the internal dynamical evolution of stellar systems
• AGB subpopulations in the nearby globular cluster NGC 6397
• NGC 6397: The metallicity trend along the isochrone revisited
• Evolution of redback radio pulsars in globular clusters
• Rotational velocities of Blue Straggler Stars in the Globular Cluster M55
• Constraints on blue straggler formation mechanisms in Galactic globular clusters from proper motion velocity distributions
• Prospects of measuring a metallicity trend and spread in globular clusters from low-resolution spectroscopy
• Detection of a white dwarf orbiting a Carbon-Oxygen depleted blue straggler in 47 Tucanae
• Globular Cluster Intrinsic Iron Abundance Spreads: I. Catalog
• Fast Rotating Blue Straggler Stars in the globular cluster NGC 1851