The Chemical Composition of Globular Clusters of Different Nature in Our Galaxy

Марсаков, В. А.; Koval, V. V.; Gozha, M. L.

doi:10.1134/s1063772919040048

Cited by 14 publications

(17 citation statements)

References 50 publications

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“…We adopt the spectroscopic estimate of metallicity [Fe/H]= −1.58 ± 0.04 (equal to Z = 0.0004 with the solar metallicity Z = 0.0152) derived for NGC 6205 by Carretta et al (2009) within their abundance scale, which is well defined from a robust dataset of [Fe/H] abundances of GCs. This estimate agrees with recent estimates from a Fourier decomposition of the light curves of RRab and RRc stars by Deras et al (2019), [Fe/H]= −1.58 ± 0.09, and from a review of chemical composition of Galactic GCs by Marsakov, Koval' & Gozha (2019), [Fe/H]= −1.54 ± 0.06.…”

Section: Some Properties Of Ngc 6205supporting

confidence: 90%

Isochrone fitting of Galactic globular clusters -- II. NGC6205 (M13)

Gontcharov,

Khovritchev,

Mosenkov

2020

Preprint

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We present new isochrone fits to colour-magnitude diagrams of the Galactic globular cluster NGC 6205 (M13). We utilise 34 photometric bands from the ultraviolet to midinfrared by use of data from the HST, Gaia DR2, SDSS, unWISE, Pan-STARRS DR1, and other photometric sources. In our isochrone fitting we use the PARSEC, MIST, DSEP, BaSTI, and IAC-BaSTI theoretical models and isochrones, both for the solarscaled and He-α-enhanced abundances, with a metallicity of about [Fe/H]= −1.58 adopted from the literature. The colour-magnitude diagrams, obtained with pairs of filters from different datasets but of similar effective wavelengths, show some colour offsets up to 0.04 mag between the fiducial sequences and isochrones. We attribute these offsets to systematic differences of the datasets. Some intrinsic systematic differences of the models/isochrones remain in our results: the derived distances and ages are different for the ultraviolet, optical and infrared photometry used, while the derived ages are different for the different models/isochrones, e.g. in the optical range from 12.3±0.7 Gyr for He-α-enhanced DSEP to 14.4±0.7 Gyr for MIST. Despite the presence of multiple stellar populations, we obtain convergent estimates for the dominant population: best-fitting distance 7.4 ± 0.2 kpc, true distance modulus 14.35 ± 0.06 mag, parallax 0.135 ± 0.004 mas, extinction A V = 0.12 ± 0.02, and reddening E(B − V) = 0.04 ± 0.01. These estimates agree with other recent estimates, however, the extinction and reddening are twice as high as generally accepted. The derived empirical extinction law agrees with the Cardelli-Clayton-Mathis extinction law with the best-fitting R V = 3.1 +1.6 −1.1 .

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Section: Some Properties Of Ngc 6205supporting

confidence: 90%

Isochrone fitting of Galactic globular clusters -- II. NGC6205 (M13)

Gontcharov,

Khovritchev,

Mosenkov

2020

Preprint

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“…Moreover, in 7 out of 9 clusters, the relationship is [Ca, Ti/Fe] > 0.2, and in two (NGC 6528 and NGC 6553) only slightly less. The three signed clusters at the bottom of the diagram in the past belonged to destroyed dwarf galaxies (Marsakov et al 2019c).…”

Section: Basic Datamentioning

confidence: 99%

Inconsistency of Chemical Properties of Stellar Populations in the Thick Disk Subsystem of our Galaxy

2020

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Using modern published data on velocities and spectroscopic definitions of chemical elements in stellar objects of the Galaxy, we investigated the relationship of chemical composition with the kinematics of different populations. The paper shows that the old stellar populations of the Galaxy, belonging (by the kinematic criterion) to the thick disk subsystem-globular clusters, field variables of the type RR Lyrae (lyrids), as well as close F-G dwarfs and field giants, have different chemical composition. In particular, the dwarfs and giants of the field are on average more metallic than the globular clusters and lyrids of the field. Moreover, the relative abundances of α-elements in the range [Fe/H] > −1.0 are the highest for globular clusters, and are the lowest for for field variables of the RR Lyrae type. Based on the analysis of the nature of the dependences of [α/Fe] on [Fe/H] for these objects it was suggested that the thick disk subsystem in the Galaxy is composite and at least three components exist independently within it. The oldest one includes metal-rich globular clusters that formed from a single proto-galactic cloud shortly after the start of type Ia supernovae outbursts. Then the subsystem of field stars of a thick disk was formed as a result of "heating" of stars of already formed thin disk of the Galaxy by a rather massive dwarf satellite galaxy that fell on it. And finally, subsystems of field stars with the kinematics of not only a thick, but even a thin disk that fell on the Galaxy from this captured satellite galaxy.

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“…All these GCs have two dominating populations (Milone et al 2017;Lardo et al 2018). Both populations are -enriched with 0.1 <[ /Fe]< 0.4 (Carretta et al 2010;Marsakov, Koval' & Gozha 2019;Horta et al 2020), but differ in helium abundance 6 . It would be reasonable to assume helium content ≈ 0.248 and ≈ 0.275 for the primordial and helium-enriched populations, respectively (Piotto et al 2013;Wagner-Kaiser et al 2016;Milone et al 2018).…”

Section: Properties Of the Clustersmentioning

confidence: 99%

Isochrone fitting of Galactic globular clusters -- III. NGC\,288, NGC\,362, and NGC\,6218 (M12)

Gontcharov,

Khovritchev,

Mosenkov

et al. 2021

Preprint

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We present new isochrone fits to colour-magnitude diagrams of the Galactic globular clusters NGC 288, NGC 362, and NGC 6218 (M12). We utilize a lot of photometric bands from the ultraviolet to mid-infrared by use of data from the HST, Gaia, unWISE, Pan-STARRS, and other photometric sources. In our isochrone fitting we use theoretical models and isochrones from the Dartmouth Stellar Evolution Program and Bag of Stellar Tracks and Isochrones for -enhanced abundance [ /Fe]= +0.40, different helium abundances, and a metallicity of about [Fe/H]= −1.3 adopted from the literature. We derive the most probable distances 8.96±0.05, 8.98±0.06, and 5.04±0.05 kpc, ages 13.5±1.1, 11.0±0.6, and 13.8±1.1 Gyr, extinctions V = 0.08±0.03, 0.11 ± 0.04, and 0.63 ± 0.03 mag, and reddenings ( − ) = 0.014 ± 0.010, 0.028 ± 0.011, and 0.189 ± 0.010 mag for NGC 288, NGC 362, and NGC 6218, respectively. The distance estimates from the different models are consistent, while those of age, extinction, and reddening are not. The uncertainties of age, extinction, and reddening are dominated by some intrinsic systematic differences between the models. However, the models agree in their relative age estimates: NGC 362 is 2.6 ± 0.5 Gyr younger than NGC 288 and 2.8 ± 0.5 Gyr younger than NGC 6218, confirming age as the second parameter for these clusters. We provide reliable lists of the cluster members and precise cluster proper motions from the Gaia Early Data Release 3.

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The Chemical Composition of Globular Clusters of Different Nature in Our Galaxy

Cited by 14 publications

References 50 publications

Isochrone fitting of Galactic globular clusters -- II. NGC6205 (M13)

Isochrone fitting of Galactic globular clusters -- II. NGC6205 (M13)

Inconsistency of Chemical Properties of Stellar Populations in the Thick Disk Subsystem of our Galaxy

Isochrone fitting of Galactic globular clusters -- III. NGC\,288, NGC\,362, and NGC\,6218 (M12)

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