Multimodal Distributions along the Horizontal Branch

Ferraro, F. R.; Paltrinieri, B.; Pecci, F. Fusi; Rood, Robert T.; Dorman, Ben

doi:10.1086/305712

Cited by 179 publications

(275 citation statements)

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“…Carretta et al 2011a;Sbordone et al 2011;Milone et al 2012;Cassisi et al 2013). tail (Ferraro et al 1998), with the concentration of blue tail stars increasing toward the cluster centre (Brocato et al 1998). M 80 presents a typical halo-type orbit, with a short period and small size, never leaving the inner 3-4 kpc of the Galaxy (Dinescu et al 1999).…”

Section: Introductionmentioning

confidence: 99%

The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)

Carretta

Bragaglia

Gratton

et al. 2015

A&A

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We present the abundance analysis of 82 red giant branch stars in the dense, metal-poor globular cluster NGC 6093 (M 80), the largest sample of stars analysed in this way for this cluster. From high-resolution UVES spectra of 14 stars and intermediate resolution GIRAFFE spectra for the other stars we derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu. On our UVES metallicity scale the mean metal abundance of M 80 is [Fe/H] = −1.791 ± 0.006 ± 0.076 (±statistical ±systematic error) with σ = 0.023 (14 stars). M 80 shows star-to-star variations in proton-capture elements, and the extension of the Na-O anti-correlation perfectly fit the relations with (i) total cluster mass; (ii) horizontal branch morphology; and (iii) cluster concentration previously found by our group. The chemistry of multiple stellar populations in M 80 does not look extreme. The cluster is also a representative of halo globular clusters concerning the pattern of α-capture and Fe-group elements. However we found that a significant contribution from the s-process is required to account for the distribution of neutron-capture elements. A minority of stars in M 80 seem to exhibit slightly enhanced abundances of s-process species, compatible with those observed in M 22 and NGC 1851, although further confirmation from larger samples is required.

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Section: Introductionmentioning

confidence: 99%

The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)

Carretta

Bragaglia

Gratton

et al. 2015

A&A

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“…Although a few of these gaps may merely be statistical fluctuations ), others could be real features, as they often show up at similar locations in different clusters. Of particular interest is the gap at T eff ' 11;000-12,000 K, labeled '' G1 '' by Ferraro et al (1998), which appears to coincide with a '' jump '' in Strömgren u-band luminosity first discovered in M13 by Grundahl, Vandenberg, & Andersen (1998). For stars cooler than $11,500 K, Grundahl et al found good agreement between the observed and theoretical BHB loci, but the hotter stars' u magnitudes were brighter than predictions by $0.4 mag.…”

Section: Introductionmentioning

confidence: 99%

Chemical Abundances and Rotation Velocities of Blue Horizontal‐Branch Stars in Six Globular Clusters

Behr

2003

ASTROPHYS J SUPPL S

143

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High-resolution spectroscopic measurements of blue horizontal-branch stars in six metal-poor globular clusters-M3, M13, M15, M68, M92, and NGC 288-reveal remarkable variations in photospheric composition and rotation velocity as a function of a star's position along the horizontal branch. For the cooler stars (T eff < 11;200 K), the derived abundances are in good agreement with the canonical cluster metallicities, and we find a wide range of v sin i rotation velocities, some as high as 40 km s À1 . In the hotter stars, however, most metal species are strongly enhanced, by as much as 3 dex, relative to the expected cluster metallicity, while helium is depleted by 2 dex or more. In addition, the hot stars all rotate slowly, with v sin i < 8 km s À1 . The anomalous abundances appear to be due to atomic diffusion mechanisms-gravitational settling of helium, and radiative levitation of metals-in the nonconvective atmospheres of these hot stars. We discuss the influence of these photospheric metal enhancements on the stars' photometric properties and explore possible explanations for the observed distribution of rotation velocities.

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“…The first evidence of the presence of a BSS bimodal distribution (Ferraro et al 1997) was found in M 3 and was later on confirmed for other clusters: M 55 (Zaggia et al 1997); 47 Tuc (Ferraro et al 2001); Pal 13 (Clark et al 2004); NGC 6752 (Sabbi et al 2004); M 5 (Warren et al 2006); and M 62 (Beccari et al 2006), while in ω Cen the bimodality seems to be ruled out .…”

Section: Article Published By Edp Sciencesmentioning

confidence: 78%

“…We will refer to BSS of the first and second types as primordial and collisional BSS. Recent results show that both formation mechanisms could be at work in a given cluster (Ferraro et al 1997;Piotto et al 2004;Davies et al 2004;Mapelli et al 2004Mapelli et al , 2006.…”

Section: Introductionmentioning

confidence: 99%

Environmental Effects on the Globular Cluster Blue Straggler Population: a Statistical Approach

Moretti

Angeli

Piotto³

2007

Proc. IAU

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Context. Blue stragglers stars (BSS) constitute an ubiquitous population of objects whose origin involves both dynamical and stellar evolution. Aims. In this paper we study the properties of a catalogue of BSS extracted from an homogeneous sample of 56 Galactic globular clusters (GC) observed with Wide-Field Planetary Camera 2 on board of Hubble Space Telescope (WFPC2/HST). Methods. With the purpose of investigating the environmental dependence of the BSS formation mechanisms, we explore possible monovariate relations between the frequency of BSS (divided in different subsamples according to their location with respect to the parent cluster core radius and half-mass radius) and the main parameters of their host GC. We also performed a principal component analysis (PCA) to extract the main parent cluster parameters, which characterise the BSS family. Results. We find that any subpopulation of BSS strongly depends on the luminosity of the cluster, on the extension of the cluster horizontal branch, and on the central velocity dispersion: more luminous clusters and clusters with a smaller central velocity dispersion have a higher BSS frequency. Moreover, we find that clusters having higher mass, higher central densities, and smaller core relaxation timescales have, on average, more luminous BSS. Finally, different dependencies seem to hold for clusters with different integrated luminosity: brighter clusters show a BSS population that depends on the collisional parameter, while BSS in fainter clusters are mostly influenced by the cluster luminosity and the dynamical timescales.

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Multimodal Distributions along the Horizontal Branch

Cited by 179 publications

References 49 publications

The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)

The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)

Chemical Abundances and Rotation Velocities of Blue Horizontal‐Branch Stars in Six Globular Clusters

Environmental Effects on the Globular Cluster Blue Straggler Population: a Statistical Approach

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