Homogeneous age dating of 55 Galactic globular clusters

Salaris, Maurizio; Weiß, Achim

doi:10.1051/0004-6361:20020554

Cited by 252 publications

(353 citation statements)

References 40 publications

(63 reference statements)

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“…Even if our purpose is only to check the general agreement between the present set of models and data, we note that our estimates for age, distance modulus and reddening are consistent, within the uncertainties, with the recent ones available in the literature (see e.g. di Cecco et al 2010;Kraft & Ivans 2003;Salaris & Weiss 2002;VandenBerg et al 2002, for M92;Kraft & Ivans 2003;Rey et al 2001;Yi et al 2001, for M3;Bergbusch & Stetson 2009;Percival et al 2002;Grundahl et al 2002, andreferences therein, Zoccali et al 2001, for 47 Tuc). We are aware that very high quality photometric data for 47 Tuc show the possible presence of multipopulation from the analysis of the subgiant branch (see e.g.…”

Section: Comparison With Observational Datasupporting

confidence: 83%

The Pisa Stellar Evolution Data Base for low-mass stars

Dell’Omodarme

Valle

Degl’Innocenti

et al. 2012

A&A

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Context. The last decade showed an impressive observational effort from the photometric and spectroscopic point of view for ancient stellar clusters in our Galaxy and beyond, leading to important and sometimes surprising results. Aims. The theoretical interpretation of these new observational results requires updated evolutionary models and isochrones spanning a wide range of chemical composition so that the possibility of multipopulations inside a stellar cluster is also taken also into account. Methods. With this aim we built the new "Pisa Stellar Evolution Database" of stellar models and isochrones by adopting a welltested evolutionary code (FRANEC) implemented with updated physical and chemical inputs. In particular, our code adopts realistic atmosphere models and an updated equation of state, nuclear reaction rates and opacities calculated with recent solar elements mixture. Results. A total of 32 646 models have been computed in the range of initial masses 0.30 ÷ 1.10 M for a grid of 216 chemical compositions with the fractional metal abundance in mass, Z, ranging from 0.0001 to 0.01, and the original helium content, Y, from 0.25 to 0.42. Models were computed for both solar-scaled and α-enhanced abundances with different external convection efficiencies. Correspondingly, 9720 isochrones were computed in the age range 8÷15 Gyr, in time steps of 0.5 Gyr. The whole database is available to the scientific community on the web. Models and isochrones were compared with recent calculations available in the literature and with the color-magnitude diagram of selected Galactic globular clusters. The dependence of relevant evolutionary quantities, namely turn-off and horizontal branch luminosities, on the chemical composition and convection efficiency were analyzed in a quantitative statistical way and analytical formulations were made available for reader's convenience. These relations can be useful in several fields of stellar evolution, e.g. evolutionary properties of binary systems, synthetic models for simple stellar populations and for star counts in galaxies, and chemical evolution models of galaxies.

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Section: Comparison With Observational Datasupporting

confidence: 83%

The Pisa Stellar Evolution Data Base for low-mass stars

Dell’Omodarme

Valle

Degl’Innocenti

et al. 2012

A&A

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“…The metal-poor clusters in Sgr appear to be approximately coeval with the oldest Galactic globular clusters (e.g., Layden & Sarajedini 2000), which according to recent studies (e.g., Salaris & Weiss 2002) have ages of 12 to 13 Gyr. The identification of Whiting 1 with Sgr suggests that this galaxy was able to form star clusters for ≈6 Gyr.…”

Section: Whiting 1 and The Star Cluster Family Of The Sgr Dsphmentioning

confidence: 78%

“…According to Sandquist (2004) and references therein, M 67 is 4 Gyr old and has approximately solar composition. M71 is much older, ∼10 Gyr, and more metal poor, [Fe/H] ∼ -0.7 (e.g., Salaris & Weiss 2002). In the upper diagram of Fig.…”

Section: Estimate Of Metallicity From the Infrared Caii Linesmentioning

confidence: 99%

“…Tables of the individual photometric measurements are available at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/181 (e.g., Salaris & Weiss 2002), whereas the onset of star formation in the thin disk, as indicated by the oldest open clusters, started later, after a hiatus of a few Gyr (Carraro et al 1999). The ages of the metal-rich globular clusters, some of which belong to the thick disk while others are part of the bulge, fall roughly in this age gap.…”

Section: Introductionmentioning

confidence: 99%

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Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy

Carraro¹,

Zinn²,

Bidin³

2007

A&A

120

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Context. Recently, Carraro (2005) drew attention to the remarkable star cluster Whiting 1 by showing that it lies about 40 kpc from the Sun and is therefore unquestionably a member of the Galactic halo (b = −60.6 deg). Its Color Magnitude Diagram (CMD) indicated that Whiting 1 is very young (∼5 Gyr) for a globular cluster. It is very likely that Whiting 1 originated in a dwarf galaxy that has since been disrupted by the Milky Way. Aims. The main goals of this investigation were to constrain better the age, metallicity, and distance of Whiting 1 and to assess whether it belongs to a stellar stream from the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Methods. Deep CCD photometry in the BVI pass-bands obtained with the VLT is used to improve the quality of the CMD and to determine the cluster's luminosity function and surface density profile. High-resolution spectrograms obtained with Magellan are used to measure the cluster's radial velocity and to place limits on its possible metallicity. The measurements of distance and radial velocity are used to test the cluster's membership in the stellar streams from the Sgr dSph. Results. From our CMD of Whiting 1, we derive new estimates for the cluster's age (6.5 +1.0 −0.5 Gyr), metallicity (Z = 0.004 ± 0.001, [Fe/H] = -0.65), and distance (29.4 +1.8 −2.0 kpc). From echelle spectrograms of three stars, we obtain -130.6 ± 1.8 km s −1 for the cluster's radial velocity and show from measurements of two infra-red CaII lines that the [Fe/H] of the cluster probably lies in the range -1.1 to -0.4. Both the luminosity function and the surface density profile suggest that the cluster has undergone tidal stripping by the Milky Way. We demonstrate that the position of Whiting 1 on the sky, its distance from the Sun, and its radial velocity are identical to within the errors of both the theoretical predictions of the trailing stream of stars from the Sgr dSph galaxy and the previous observations of the M giant stars that delineate the streams. Conclusions. With the addition of Whiting 1, there is now strong evidence that 6 globular clusters formed within the Sgr dSph. Whiting 1 is particularly interesting because it is the youngest and among the most metal rich. The relatively young age of Whiting 1 demonstrates that this dwarf galaxy was able to form star clusters for a period of at least 6 Gyr, and the age and metallicity of Whiting 1 are consistent with the age-metallicity relationship in the main body of the Sgr dSph. The presence now of Whiting 1 in the Galactic halo provides additional support for the view that the young halo clusters originated in dwarf galaxies that have been accreted by the Milky Way.

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“…Past observations have shown that galactic metal-poor GCs tend to be older than metal-rich GCs and the age spread in metal-poor GCs is ∼ 1 Gyr compared to the ∼ 6 Gyr dispersion in metal-rich GCs (Rosenberg et al 1999;Salaris & Weiss 2002;Marín-Franch et al 2009). There is some evidence of self enrichment in GCs; however, the age gap between metal-poor and metal-rich GCs is greater than the range present within each population suggesting that these are two distinct populations (Marín-Franch et al 2009).…”

mentioning

confidence: 96%

Clues on the missing sources of reionization from self-consistent modelling of Milky Way and dwarf galaxy globular clusters

Katz¹,

Ricotti²

2014

Monthly Notices of the Royal Astronomical Society

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Globular clusters are unique tracers of ancient star formation. We determine the formation efficiencies of globular clusters across cosmic time by modeling the formation and dynamical evolution of the globular cluster population of a Milky Way type galaxy in hierarchical cosmology, using the merger tree from the Via Lactea II simulation. All of the models are constrained to reproduce the observed specific frequency and initial mass function of globular clusters in isolated dwarfs. Globular cluster orbits are then computed in a time varying gravitational potential after they are either accreted from a satellite halo or formed in situ, within the Milky Way halo.We find that the Galactocentric distances and metallicity distribution of globular clusters are very sensitive to the formation efficiencies of globular clusters as a function of redshift and halo mass. Our most accurate models reveal two distinct peaks in the globular cluster formation efficiency at z ∼ 2 and z ∼ 7 − 12 and prefer a formation efficiency that is mildly increasing with decreasing halo mass, the opposite of what expected for feedback-regulated star formation. This model accurately reproduces the positions, velocities, mass function, metallicity distribution, and age distribution of globular clusters in the Milky Way and predicts that ∼ 40% formed in situ, within the Milky Way halo, while the other ∼ 60% were accreted from about 20 satellite dwarf galaxies with v cir > 30 km/s, and about 29% or all globular clusters formed at redshifts z > 7.These results further strengthen the notion that globular cluster formation was an important mode of star formation in high-redshift galaxies and likely played a significant role in the reionization of the intergalactic medium.

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Homogeneous age dating of 55 Galactic globular clusters

Cited by 252 publications

References 40 publications

The Pisa Stellar Evolution Data Base for low-mass stars

The Pisa Stellar Evolution Data Base for low-mass stars

Whiting 1: the youngest globular cluster associated with the Sagittarius dwarf spheroidal galaxy

Clues on the missing sources of reionization from self-consistent modelling of Milky Way and dwarf galaxy globular clusters

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