Context.
Many of the open clusters listed in modern catalogues were initially reported by visual astronomers as apparent overdensities of bright stars. As observational techniques and analysis ...methods continue to improve, some of them have been shown to be chance alignments of stars and not true clusters. Recent publications making use of
Gaia
DR2 data have provided membership lists for over a thousand clusters, however, many nearby objects listed in the literature have so far evaded detection.
Aims.
We aim to update the
Gaia
DR2 cluster census by performing membership determinations for known clusters that had been missed by previous studies and for recently-discovered clusters. We investigate a sub-set of non-detected clusters that, according to their literature parameters, should be easily visible in
Gaia
. Confirming or disproving the existence of old, inner-disc, high-altitude clusters is especially important as their survival or disruption is linked to the dynamical processes that drive the evolution of the Milky Way.
Methods.
We employed the
Gaia
DR2 catalogue and a membership assignment procedure, as well as visual inspections of spatial, proper motion, and parallax distributions. We used membership lists provided by other authors when available.
Results.
We derived membership lists for 150 objects, including ten that were already known prior to
Gaia
. We compiled a final list of members for 1481 clusters. Among the objects that we are still unable to identify with the
Gaia
data, we argue that many (mostly putatively old, relatively nearby, high-altitude objects) are not true clusters.
Conclusions.
At present, the only confirmed cluster located further than 500 pc away from the Galactic plane within the Solar circle is NGC 6791. It is likely that the objects discussed in this study only represent a fraction of the non-physical groupings erroneously listed in the catalogues as genuine open clusters and that those lists need further cleaning.
Combining the precise parallaxes and optical photometry delivered by Gaia’s second data release with the photometric catalogues of Pan-STARRS1, 2MASS, and AllWISE, we derived Bayesian stellar ...parameters, distances, and extinctions for 265 million of the 285 million objects brighter than G = 18. Because of the wide wavelength range used, our results substantially improve the accuracy and precision of previous extinction and effective temperature estimates. After cleaning our results for both unreliable input and output data, we retain 137 million stars, for which we achieve a median precision of 5% in distance, 0.20 mag in V-band extinction, and 245 K in effective temperature for G ≤ 14, degrading towards fainter magnitudes (12%, 0.20 mag, and 245 K at G = 16; 16%, 0.23 mag, and 260 K at G = 17, respectively). We find a very good agreement with the asteroseismic surface gravities and distances of 7000 stars in the Kepler, K2-C3, and K2-C6 fields, with stellar parameters from the APOGEE survey, and with distances to star clusters. Our results are available through the ADQL query interface of the Gaia mirror at the Leibniz-Institut für Astrophysik Potsdam (gaia.aip.de) and as binary tables at data.aip.de. As a first application, we provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps as a function of distance, and extensive density maps. These demonstrate the potential of our value-added dataset for mapping the three-dimensional structure of our Galaxy. In particular, we see a clear manifestation of the Galactic bar in the stellar density distributions, an observation that can almost be considered direct imaging of the Galactic bar.
Context.
The large astrometric and photometric survey performed by the
Gaia
mission allows for a panoptic view of the Galactic disc and its stellar cluster population. Hundreds of stellar clusters ...were only discovered after the latest
Gaia
data release (DR2) and have yet to be characterised.
Aims.
Here we make use of the deep and homogeneous
Gaia
photometry down to
G
= 18 to estimate the distance, age, and interstellar reddening for about 2000 stellar clusters identified with
Gaia
DR2 astrometry. We use these objects to study the structure and evolution of the Galactic disc.
Methods.
We relied on a set of objects with well-determined parameters in the literature to train an artificial neural network to estimate parameters from the
Gaia
photometry of cluster members and their mean parallax.
Results.
We obtain reliable parameters for 1867 clusters. Our catalogue confirms the relative lack of old stellar clusters in the inner disc (with a few notable exceptions). We also quantify and discuss the variation of scale height with cluster age, and we detect the Galactic warp in the distribution of old clusters.
Conclusions.
This work results in a large and homogeneous cluster catalogue, allowing one to trace the structure of the disc out to distances of ∼4 kpc. However, the present sample is still unable to trace the outer spiral arm of the Milky Way, which indicates that the outer disc cluster census might still be incomplete.
Context.
Open clusters are key targets for studies of Galaxy structure and evolution, and stellar physics. Since the
Gaia
data release 2 (DR2), the discovery of undetected clusters has shown that ...previous surveys were incomplete.
Aims.
Our aim is to exploit the Big Data capabilities of machine learning to detect new open clusters in
Gaia
DR2, and to complete the open cluster sample to enable further studies of the Galactic disc.
Methods.
We use a machine-learning based methodology to systematically search the Galactic disc for overdensities in the astrometric space and identify the open clusters using photometric information. First, we used an unsupervised clustering algorithm, DBSCAN, to blindly search for these overdensities in
Gaia
DR2 (
l
,
b
,
ϖ
,
μ
α
*
,
μ
δ
), and then we used a deep learning artificial neural network trained on colour–magnitude diagrams to identify isochrone patterns in these overdensities, and to confirm them as open clusters.
Results.
We find 582 new open clusters distributed along the Galactic disc in the region |
b
| < 20°. We detect substructure in complex regions, and identify the tidal tails of a disrupting cluster
UBC 274
of ∼3 Gyr located at ∼2 kpc.
Conclusions.
Adapting the mentioned methodology to a Big Data environment allows us to target the search using the physical properties of open clusters instead of being driven by computational limitations. This blind search for open clusters in the Galactic disc increases the number of known open clusters by 45%.
ABSTRACT
Reliable fundamental parameters of open clusters (OCs) such as distance, age, and extinction are key to our understanding of Galactic structure and stellar evolution. In this work, we use ...Gaia Data Release 2 (DR2) to investigate 45 OCs listed in the New catalogue of optically visible open clusters and candidates (DAML) but with no previous astrometric membership estimation based on Gaia DR2. In the process of selecting targets for this study, we found that some clusters reported as new discoveries in recent papers based on Gaia DR2 were already known clusters listed in DAML. Cluster memberships were determined using a maximum likelihood method applied to Gaia DR2 astrometry. This has allowed us to estimate mean proper motions and mean parallaxes for all investigated clusters. Mean radial velocities were also determined for 12 clusters, 7 of which had no previous published values. We have improved our isochrone fitting code to account for interstellar extinction using an updated extinction polynomial for the Gaia DR2 photometric bandpasses and the Galactic abundance gradient as a prior for metallicity. The updated procedure was validated with a sample of clusters with high-quality Fe/H determinations. We then did a critical review of the literature and verified that our cluster parameter determinations represent a substantial improvement over previous values.
We present a catalogue of 362 million stellar parameters, distances, and extinctions derived from
Gaia
’s Early Data Release (EDR3) cross-matched with the photometric catalogues of Pan-STARRS1, ...SkyMapper, 2MASS, and AllWISE. The higher precision of the
Gaia
EDR3 data, combined with the broad wavelength coverage of the additional photometric surveys and the new stellar-density priors of the
StarHorse
code, allows us to substantially improve the accuracy and precision over previous photo-astrometric stellar-parameter estimates. At magnitude
G
= 14 (17), our typical precisions amount to 3% (15%) in distance, 0.13 mag (0.15 mag) in
V
-band extinction, and 140 K (180 K) in effective temperature. Our results are validated by comparisons with open clusters, as well as with asteroseismic and spectroscopic measurements, indicating systematic errors smaller than the nominal uncertainties for the vast majority of objects. We also provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps, and extensive stellar density maps that reveal detailed substructures in the Milky Way and beyond. The new density maps now probe a much greater volume, extending to regions beyond the Galactic bar and to Local Group galaxies, with a larger total number density. We publish our results through an ADQL query interface (
gaia.aip.de
) as well as via tables containing approximations of the full posterior distributions. Our multi-wavelength approach and the deep magnitude limit render our results useful also beyond the next
Gaia
release, DR3.
Context.
Open clusters (OCs) trace the evolution of the Galactic disc with great accuracy.
Gaia
and large ground-based spectroscopic surveys make it possible to determine their properties and study ...their kinematics with unprecedented precision.
Aims.
We study the kinematical behaviour of the OC population over time. We take advantage of the latest age determinations of OCs to investigate the correlations of the 6D phase-space coordinates and orbital properties with age. The phase-space distribution, age-velocity relation, and action distribution are compared to those of field stars. We also investigate the rotation curve of the Milky Way traced by OCs, and we compare it to that of other observational or theoretical studies.
Methods.
We gathered nearly 30 000 radial velocity (RV) measurements of OC members from both
Gaia
-RVS data and ground-based surveys and catalogues. We computed the weighted mean RV, Galactic velocities, and orbital parameters of 1382 OCs. We investigated their distributions as a function of age and by comparison to field stars.
Results.
We provide the largest RV catalogue available for OCs, half of it based on at least three members. Compared to field stars, we note that OCs are not on exactly the same arches in the radial-azimuthal velocity plane, while they seem to follow the same diagonal ridges in the Galactic radial distribution of azimuthal velocities. Velocity ellipsoids in different age bins all show a clear anisotropy. The heating rate of the OC population is similar to that of field stars for the radial and azimuthal components, but it is significantly lower for the vertical component. The rotation curve drawn by our sample of clusters shows several dips that match the wiggles derived from nonaxisymmetric models of the Galaxy. From the computation of orbits, we obtain a clear dependence of the maximum height and eccentricity on age. Finally, the orbital characteristics of the sample of clusters as shown by the action variables follow the distribution of field stars. The additional age information of the clusters indicates some (weak) age dependence of the known moving groups.
Open cluster kinematics with Gaia DR2 Soubiran, C.; Cantat-Gaudin, T.; Romero-Gómez, M. ...
Astronomy and astrophysics (Berlin),
11/2018, Letnik:
619
Journal Article
Recenzirano
Odprti dostop
Context. Open clusters are very good tracers of the evolution of the Galactic disc. Thanks to Gaia, their kinematics can be investigated with an unprecedented precision and accuracy. Aims. The ...distribution of open clusters in the 6D phase space is revisited with Gaia DR2. Methods. The weighted mean radial velocity of open clusters was determined, using the most probable members available from a previous astrometric investigation that also provided mean parallaxes and proper motions. Those parameters, all derived from Gaia DR2 only, were combined to provide the 6D phase-space information of 861 clusters. The velocity distribution of nearby clusters was investigated, as well as the spatial and velocity distributions of the whole sample as a function of age. A high-quality subsample was used to investigate some possible pairs and groups of clusters sharing the same Galactic position and velocity. Results. For the high-quality sample of 406 clusters, the median uncertainty of the weighted mean radial velocity is 0.5 km s−1. The accuracy, assessed by comparison to ground-based high-resolution spectroscopy, is better than 1 km s−1. Open clusters nicely follow the velocity distribution of field stars in the close solar neighbourhood as previously revealed by Gaia DR2. As expected, the vertical distribution of young clusters is very flat, but the novelty is the high precision to which this can be seen. The dispersion of vertical velocities of young clusters is at the level of 5 km s−1. Clusters older than 1 Gyr span distances to the Galactic plane of up to 1 kpc with a vertical velocity dispersion of 14 km s−1, typical of the thin disc. Five pairs of clusters and one group with five members might be physically related. Other binary candidates that have been identified previously are found to be chance alignments.
Context. The Vela OB2 association is a group of ∼10 Myr stars exhibiting a complex spatial and kinematic substructure. The all-sky Gaia DR2 catalogue contains proper motions, parallaxes (a proxy for ...distance), and photometry that allow us to separate the various components of Vela OB2. Aims. We characterise the distribution of the Vela OB2 stars on a large spatial scale, and study its internal kinematics and dynamic history. Methods. We make use of Gaia DR2 astrometry and published Gaia-ESO Survey data. We apply an unsupervised classification algorithm to determine groups of stars with common proper motions and parallaxes. Results. We find that the association is made up of a number of small groups, with a total current mass over 2330 M⊙. The three-dimensional distribution of these young stars trace the edge of the gas and dust structure known as the IRAS Vela Shell across ∼180 pc and shows clear signs of expansion. Conclusions. We propose a common history for Vela OB2 and the IRAS Vela Shell. The event that caused the expansion of the shell happened before the Vela OB2 stars formed, imprinted the expansion in the gas the stars formed from, and most likely triggered star formation.
Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise ...astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.
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