Gaia parallax of Milky Way globular clusters – A solution of mixture model

Shao, Zhengyi; Li, Lu

doi:10.1093/mnras/stz2317

Cited by 20 publications

(13 citation statements)

References 31 publications

(33 reference statements)

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“…Using Gaia parallaxes, Chen et al (2018) obtained a distance of 4.45 kpc ± 0.01 (random) ± 0.12 (systematic) to 47 Tuc (we note that the recent paper by Shao & Li (2019) has not improved on their results).…”

Section: Distance Estimatementioning

confidence: 80%

The Cluster AgeS Experiment (CASE) – VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries

Thompson

Udalski

Dotter

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We use photometric and spectroscopic observations of the eclipsing binary E32 in the globular cluster 47 Tuc to derive the masses, radii, and luminosities of the component stars. The system has an orbital period of 40.9d, a markedly eccentric orbit with e = 0.24, and is shown to be a member of or a recent escaper from the cluster. We obtain M p = 0.862 ± 0.005M ⊙ , R p = 1.183 ± 0.003R ⊙ , L p = 1.65 ± 0.05L ⊙ for the primary and M s = 0.827 ± 0.005M ⊙ , R s = 1.004 ± 0.004R ⊙ , L s = 1.14 ± 0.04L ⊙ for the secondary. Based on these data and on an earlier analysis of the binary V69 in 47 Tuc we measure the distance to the cluster from the distance moduli of the component stars, and, independently, from a color -surface brightness calibration. We obtain 4.55±0.03 and 4.50±0.07 kpc, respectively -values compatible within 1 σ with recent estimates based on Gaia DR2 parallaxes. By comparing the M − R diagram of the two binaries and the color-magnitude diagram of 47 Tuc to Dartmouth model isochrones we estimate the age of the cluster to be 12.0 ± 0.5 Gyr, and the helium abundance of the cluster to be Y≈0.25.

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Section: Distance Estimatementioning

confidence: 80%

The Cluster AgeS Experiment (CASE) – VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries

Thompson

Udalski

Dotter

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The strategy of our approach is using the mixture model method, which is a natural statistical method for many situations in astronomy (Kuhn & Feigelson 2017). It is verified that even in a heavily mixed case, like the parallax distributions of field stars and members of distant globular clusters (Shao & Li 2019), the mixture model method can also fit the distribution parameters precisely.…”

Section: Model and Algorithmmentioning

confidence: 89%

Modelling unresolved binaries of open clusters in color-magnitude diagram. I. method and application of NGC3532

Li,

Shao,

et al. 2020

Preprint

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The binary properties of open clusters place crucial constraints on star formation theory and clusters' dynamical evolution. We develop a comprehensive approach that models the color-magnitude diagram (CMD) of the cluster members as the mixture of single stars and photometric unresolved binaries. This method enables us to infer the binary properties, including the binary fraction f b and binary massratio distribution index γ q when a power-law is assumed, with high accuracy and precision, which were unfeasible in conventional methods. We employ a modified Gaussian process to determine the main sequence ridge line and its scatter from the observed CMD as model input. As a first example, we apply the method to the open cluster NGC3532 with the Gaia DR2 photometry. For the cluster members within a magnitude range corresponding to FGK dwarfs, we obtain f b = 0.267 ± 0.019 and γ q = −0.10 ± 0.22 for binaries with mass ratio q > 0.2. The f b value is consistent with the previous work on NGC3532 and smaller than that of field stars. The close to zero γ q indicates that the mass ratios of binaries follow a nearly uniform distribution. For the first time, we unveil that the stars with smaller mass or in the inner region tend to have lower f b and more positive value of γ q due to the lack of low mass-ratio binaries. The clear dependences of binary properties on mass and radius are most likely caused by the internal dynamics.

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“…The DR2 offset was calibrated from quasars, which are bluer than the bulk of ω Cen stars and only cover a small fraction of their magnitude range. The DR2 parallax estimates for ω Cen by Gaia Collaboration et al (2018a) and by Shao & Li (2019) are 0.1237 ± 0.0011 and 0.1368 ± 0.0015 mas, respectively, and are substantially smaller than other determinations, presumably because the parallax offset estimated by Lindegren et al (2018) on the basis of quasar data is much smaller than the values found for brighter stars (Riess et al 2018;Arenou et al 2018;Zinn et al 2019). Our own analysis of the DR2 parallax data for stars in ω Cen revealed a large trend of parallax with star magnitude and color, leaving us to conclude that a parallax from DR2 was not reliable without further characterization of its parallax offset.…”

Section: Comparison With Prior Distance Measurements For ω Cenmentioning

confidence: 94%

The Parallax of Omega Centauri Measured from Gaia EDR3 and a Direct, Geometric Calibration of the Tip of the Red Giant Branch and the Hubble Constant

Soltis,

Casertano,

Riess

2020

Preprint

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We use data from the ESA Gaia mission Early Data Release 3 (EDR3) to measure the trigonometric parallax of ω Cen, the first high precision parallax measurement for the most massive globular cluster in the Milky Way. We use a combination of positional and high quality proper motion data from EDR3 to identify over 100,000 cluster members, of which 67,000 are in the magnitude and color range where EDR3 parallaxes are best calibrated. We find the estimated parallax to be robust, demonstrating good control of systematics within the color-magnitude diagram of the cluster. We find a parallax for the cluster of 0.191 ± 0.001 (statistical) ±0.004 (systematic) mas (2.2% total uncertainty) corresponding to a distance of 5.24 ± 0.11 kpc. The parallax of ω Cen provides a unique opportunity to directly and geometrically calibrate the luminosity of the Tip of the Red Giant Branch (TRGB) because it is the only cluster with sufficient mass to provide enough red giant stars, more than 100 one magnitude below the tip, for a precise, model-free measurement of the tip. Combined with the pre-existing and most widelyused measurements of the tip and foreground Milky Way extinction, we find M I,T RGB = −3.97 ± 0.06 mag for the I-band luminosity of the blue edge. Using the TRGB luminosity calibrated from the Gaia EDR3 parallax of ω Cen to calibrate the luminosity of SNIa results in a value for the Hubble constant of H 0 = 72.1 ± 2.0 km s −1 Mpc −1 . We make the data for the stars in ω Cen available electronically and encourage independent analyses of the results presented here.

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Gaia parallax of Milky Way globular clusters – A solution of mixture model

Cited by 20 publications

References 31 publications

The Cluster AgeS Experiment (CASE) – VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries

The Cluster AgeS Experiment (CASE) – VIII. Age and distance of the Globular Cluster 47 Tuc from the analysis of two detached eclipsing binaries

Modelling unresolved binaries of open clusters in color-magnitude diagram. I. method and application of NGC3532

The Parallax of Omega Centauri Measured from Gaia EDR3 and a Direct, Geometric Calibration of the Tip of the Red Giant Branch and the Hubble Constant

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