The <i>Gaia</i> DR2 parallax zero-point: hierarchical modelling of red clump stars

Chan, V.; Bovy, Jo

doi:10.1093/mnras/staa571

Cited by 54 publications

(49 citation statements)

References 37 publications

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“…Regarding the Gaia DR2 parallaxes, as reported by Lindegren et al (2018) and confirmed by several other works (Chan & Bovy 2020;Riess et al 2018;Schönrich et al 2019;Stassun & Torres 2018;Zinn et al 2019), there is a zero-point offset that needs to be considered. For the remainder of this paper, we adopt the global mean value of 29 µas for all the clusters (in the sense that the Gaia parallaxes are too small) reported by Lindegren et al (2018), with the exception of NGC 6811, for which we adopt the Kepler field 53 µas value from Zinn et al (2019).…”

Section: Gaia Dr2 Datamentioning

confidence: 51%

Stellar Rotation in the Gaia Era: Revised Open Clusters’ Sequences

Godoy-Rivera

Pinsonneault

Rebull

2021

ApJS

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The period versus mass diagrams (i.e., rotational sequences) of open clusters provide crucial constraints for angular momentum evolution studies. However, their memberships are often heavily contaminated by field stars, which could potentially bias the interpretations. In this paper, we use data from Gaia DR2 to reassess the memberships of seven open clusters with ground- and space-based rotational data, and present an updated view of stellar rotation as a function of mass and age. We use the Gaia astrometry to identify the cluster members in phase space, and the photometry to derive revised ages and place the stars on a consistent mass scale. Applying our membership analysis to the rotational sequences reveals that: (1) the contamination in clusters observed from the ground can reach up to ∼35%; (2) the overall fraction of rotational outliers decreases substantially when the field contaminants are removed, but some outliers persist; (3) there is a sharp upper edge in the rotation periods at young ages; (4) at young ages, stars in the 1.0–0.6M ⊙ range inhabit a global maximum of rotation periods, potentially providing an optimal window for habitable planets. Additionally, we see clear evidence for a strongly mass-dependent spin-down process. In the regime where rapid rotators are leaving the saturated domain, the rotational distributions broaden (in contradiction with popular models), which we interpret as evidence that the torque must be lower for rapid rotators than for intermediate ones. The cleaned rotational sequences from ground-based observations can be as constraining as those obtained from space.

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Section: Gaia Dr2 Datamentioning

confidence: 51%

Stellar Rotation in the Gaia Era: Revised Open Clusters’ Sequences

Godoy-Rivera

Pinsonneault

Rebull

2021

ApJS

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“…The presence of a zero-point offset in the parallaxes published in Gaia DR2 has been established both in papers describing Gaia data (Lindegren et al 2018) and by comparison with independent distance determinations (e.g., see Riess et al 2018;Stassun & Torres 2018;Khan et al 2019;Hall et al 2019;Zinn et al 2019;Schönrich et al 2019;Chan & Bovy 2020). Such an offset is largely due to a degeneracy between the parallax and the basic-angle variation of the Gaia satellite.…”

Section: Caveats and Prospectsmentioning

confidence: 92%

Age dissection of the Milky Way discs: Red giants in theKeplerfield

Miglio

Chiappini

Mackereth

et al. 2021

A&A

133

124

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Ensemble studies of red-giant stars with exquisite asteroseismic (Kepler), spectroscopic (APOGEE), and astrometric (Gaia) constraints offer a novel opportunity to recast and address long-standing questions concerning the evolution of stars and of the Galaxy. Here, we infer masses and ages for nearly 5400 giants with available Kepler light curves and APOGEE spectra using the code PARAM, and discuss some of the systematics that may affect the accuracy of the inferred stellar properties. We then present patterns in mass, evolutionary state, age, chemical abundance, and orbital parameters that we deem robust against the systematic uncertainties explored. First, we look at age-chemical-abundances ([Fe/H] and [α/Fe]) relations. We find a dearth of young, metal-rich ([Fe/H] > 0.2) stars, and the existence of a significant population of old (8−9 Gyr), low-[α/Fe], super-solar metallicity stars, reminiscent of the age and metallicity of the well-studied open cluster NGC 6791. The age-chemo-kinematic properties of these stars indicate that efficient radial migration happens in the thin disc. We find that ages and masses of the nearly 400 α-element-rich red-giant-branch (RGB) stars in our sample are compatible with those of an old (∼11 Gyr), nearly coeval, chemical-thick disc population. Using a statistical model, we show that the width of the observed age distribution is dominated by the random uncertainties on age, and that the spread of the inferred intrinsic age distribution is such that 95% of the population was born within ∼1.5 Gyr. Moreover, we find a difference in the vertical velocity dispersion between low- and high-[α/Fe] populations. This discontinuity, together with the chemical one in the [α/Fe] versus [Fe/H] diagram, and with the inferred age distributions, not only confirms the different chemo-dynamical histories of the chemical-thick and thin discs, but it is also suggestive of a halt in the star formation (quenching) after the formation of the chemical-thick disc. We then exploit the almost coeval α-rich population to gain insight into processes that may have altered the mass of a star along its evolution, which are key to improving the mapping of the current, observed, stellar mass to the initial mass and thus to the age. Comparing the mass distribution of stars on the lower RGB (R < 11 R⊙) with those in the red clump (RC), we find evidence for a mean integrated RGB mass loss ⟨ΔM⟩ = 0.10 ± 0.02 M⊙. Finally, we find that the occurrence of massive (M ≳ 1.1 M⊙) α-rich stars is of the order of 5% on the RGB, and significantly higher in the RC, supporting the scenario in which most of these stars had undergone an interaction with a companion.

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“…The resulting uncertainty of the intercepts is ∼0.1 mag, and it was added quadratically to the systematics. We converted the reddening free magnitudes into distances using the distance modulus and assuming an absolute magnitude of M K s = −1.59 ± 0.04 for RC stars, which was computed by averaging over the values obtained by Groenewegen (2008), Hawkins et al (2017), and Chan & Bovy (2020). The uncertainty corresponds to the standard deviation of the measurements.…”

Section: Reddening Vector and Distancesmentioning

confidence: 99%

Distance to three molecular clouds in the central molecular zone

Nogueras-Lara

Schödel

Neumayer

et al. 2021

A&A

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Context. The determination of absolute and relative distances of molecular clouds along the line-of-sight towards the central molecular zone (CMZ) is crucial for inferring its orbital structure and dynamics and for understanding star formation in the clouds. Aims. Recent work has suggested that the G0.253+0.016 cloud (the Brick) does not belong to the CMZ. This motivated us to crosscheck those results, computing the absolute and relative distances to the Brick as well as to another two molecular clouds (the 50 km s−1 and the 20 km s−1 clouds), and discuss their CMZ membership. Methods. We used the colour magnitude diagrams Ks versus H − Ks to compare stars detected towards the target clouds with stars detected towards three reference regions in the nuclear stellar disc (NSD) and the Galactic bulge. We used red clump (RC) stars to estimate the distance to each region. Results. We found that all the clouds present a double RC feature. Such a double RC has been reported in previous work for the NSD, but not for the bulge adjacent to it. We exclude the possibility that the different RC features are located at significantly different distances. The obtained absolute and relative distances are compatible with the Galactic centre distance (∼8 kpc).

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The Gaia DR2 parallax zero-point: hierarchical modelling of red clump stars

Cited by 54 publications

References 37 publications

Stellar Rotation in the Gaia Era: Revised Open Clusters’ Sequences

Stellar Rotation in the Gaia Era: Revised Open Clusters’ Sequences

Age dissection of the Milky Way discs: Red giants in theKeplerfield

Distance to three molecular clouds in the central molecular zone

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