The Large Early Galaxy Astrophysics Census (LEGA-C) Data Release 2: Dynamical and Stellar Population Properties of
                    z
                    ≲ 1 Galaxies in the COSMOS Field

Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented. Aims. We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. Methods. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. Results. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Conclusions. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.

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Magellanic Clouds Proper Motion and Rotation with Gaia DR1

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005580 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 249-250

Author(s):

J. Sahlmann ◽

R. van der Marel

Keyword(s):

Proper Motion ◽

Stellar Population ◽

External Validation ◽

Magellanic Clouds ◽

Data Sets ◽

Proper Motions ◽

Gaia Dr1 ◽

Data Release ◽

Motion Measurements ◽

Similar Accuracy

AbstractWe used the Gaia data release 1 to study the proper motion fields of the Large and Small Magellanic Clouds (LMC, SMC) on the basis of the Tycho-Gaia Astrometric Solution (van der Marel & Sahlmann 2016). The Gaia LMC and SMC proper motions have similar accuracy and agree to within the uncertainties with existing HST proper motion measurements. Since Gaia probes the young stellar population and uses different methods with different systematics, this provides an external validation of both data sets and their underlying approaches.

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Reviving old controversies: is the early Galaxy flat or round?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937016 ◽

2020 ◽

Vol 636 ◽

pp. A115 ◽

Cited By ~ 3

Author(s):

P. Di Matteo ◽

M. Spite ◽

M. Haywood ◽

P. Bonifacio ◽

A. Gómez ◽

...

Keyword(s):

Stellar Population ◽

Milky Way ◽

Galactic Disc ◽

Chemical Abundances ◽

First Stars ◽

Thick Disc ◽

Large Program ◽

The Galaxy ◽

Early Galaxy ◽

Two Populations

We analysed a set of very metal-poor stars, for which accurate chemical abundances have been obtained as part of the ESO Large Program “First stars” in the light of the Gaia DR2 data. The kinematics and orbital properties of the stars in the sample show they probably belong to the thick disc, partially heated to halo kinematics, and to the accreted Gaia Sausage-Enceladus satellite. The continuity of these properties with stars at both higher ([Fe/H] > −2) and lower metallicities ([Fe/H] < −4.) suggests that the Galaxy at [Fe/H] ≲ −0.5 and down to at least [Fe/H] ∼ −6 is dominated by these two populations. In particular, we show that the disc extends continuously from [Fe/H] ≤ −4 (where stars with disc-like kinematics have recently been discovered) up to [Fe/H] ≥ −2, the metallicity regime of the Galactic thick disc. An “ultra metal-poor thick disc” does indeed exist, constituting the extremely metal-poor tail of the canonical Galactic thick disc, and extending the latter from [Fe/H] ∼ −0.5 up to the most metal-poor stars discovered in the Galaxy to date. These results suggest that the disc may be the main, and possibly the only, stellar population that has formed in the Galaxy at these metallicities. This would mean that the dissipative collapse that led to the formation of the old Galactic disc must have been extremely fast. We also discuss these results in the light of recent simulation efforts made to reproduce the first stages of Milky Way-type galaxies.

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Another relic bulge globular cluster: ESO 456-SC38 (Djorgovski 2)

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935726 ◽

2019 ◽

Vol 627 ◽

pp. A145 ◽

Cited By ~ 6

Author(s):

S. Ortolani ◽

E. V. Held ◽

D. Nardiello ◽

S. O. Souza ◽

B. Barbuy ◽

...

Keyword(s):

Globular Clusters ◽

Stellar Population ◽

Milky Way ◽

Galactic Center ◽

Horizontal Branch ◽

Very Old ◽

Orbital Parameters ◽

Data Release ◽

Best Fitting ◽

Bulge Formation

Context. The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of [Fe/H] ∼ −1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way. Aims. The aim of this work is to determine an accurate distance and metallicity for ESO 456-SC38, as well as orbital parameters, in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry. This is a considerably fainter cluster that is contaminated by a rich stellar field; it is also quite absorbed by the dusty foreground. Methods. We analyzed ESO 456-SC38 based on HST photometry, with the filters F606W from ACS, F110W and F160W from WFC3, and photometry in V and I from FORS2 at the VLT. We combined this with identified stars that are covered by Gaia Data Release 2. Results. The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method. We derive an accurate distance of d⊙ = 8.75 ± 0.12 kpc and a reddening of E(B−V) = 0.81+0.02−0.02. The best-fitting BaSTI isochrones correspond to an age of 12.70+0.72−0.69 Gyr and a metallicity of [Fe/H] = −1.11+0.03−0.03. Conclusions. ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge. It has a blue horizontal branch and is very old. The cluster is confined to the bulge and bar region, but it does not support the Galactic bar structure. The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation. Studying them also provides indications on the formation times of the globular clusters themselves.

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The eye of Gaia on globular clusters structure: tidal tails

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1209 ◽

2020 ◽

Vol 495 (2) ◽

pp. 2222-2233 ◽

Cited By ~ 3

Author(s):

A Sollima

Keyword(s):

Globular Clusters ◽

Stellar Population ◽

Milky Way ◽

Field Of View ◽

Proper Motions ◽

Mixture Modelling ◽

Background Density ◽

Data Release ◽

Observational Estimate ◽

Tidal Tails

ABSTRACT I analyse the projected density distribution of member stars over a wide area surrounding 18 Galactic globular clusters using the photometric and astrometric information provided by the second data release of the Gaia mission. A 5D mixture modelling technique has been employed to optimally isolate the signal of the cluster stellar population from the contamination of the Galactic field, taking advantage of its different distribution in the space formed by colours, magnitudes, parallaxes, and proper motions. In 7 clusters I detect collimated overdensities at a >3σ level above the background density extending well beyond the cluster tidal radius, consistent with the distortion expected as a result of the tidal interaction with the Milky Way potential. In five of these clusters (NGC 288, NGC 2298, NGC 5139, NGC 6341, and NGC 7099) spectacular tidal tails extend up to the border of the analysed field of view at 5 deg from the centre. At large distances from the cluster centre, the orientation of the detected overdensities appears to be systematically aligned with the cluster orbital path, in agreement with the predictions of N-body simulations. The fraction of stars contained in the tidal tails of these clusters is also used to determine the first observational estimate of their present-day destruction rates.

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The Large Early Galaxy Astrophysics Census (LEGA-C) Data Release 3: 3000 High-quality Spectra of K s -selected Galaxies at z > 0.6

The Astrophysical Journal Supplement Series ◽

10.3847/1538-4365/ac1356 ◽

2021 ◽

Vol 256 (2) ◽

pp. 44

Author(s):

Arjen van der Wel ◽

Rachel Bezanson ◽

Francesco D’Eugenio ◽

Caroline Straatman ◽

Marijn Franx ◽

...

Keyword(s):

High Quality ◽

Data Release ◽

Early Galaxy

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Statistical criteria of stellar population types

Symposium - International Astronomical Union ◽

10.1017/s0074180900053304 ◽

1966 ◽

Vol 24 ◽

pp. 101-110

Author(s):

W. Iwanowska

Keyword(s):

Stellar Population ◽

Chemical Properties ◽

Spectrophotometric Study ◽

Physical And Chemical Properties ◽

Population Type ◽

The Galaxy ◽

Distribution Parameters ◽

Physical And Chemical ◽

Statistical Criteria ◽

And Chemical Properties

In connection with the spectrophotometric study of population-type characteristics of various kinds of stars, a statistical analysis of kinematical and distribution parameters of the same stars is performed at the Toruń Observatory. This has a twofold purpose: first, to provide a practical guide in selecting stars for observing programmes, second, to contribute to the understanding of relations existing between the physical and chemical properties of stars and their kinematics and distribution in the Galaxy.

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