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تسجيل مستخدم جديدExtended stellar systems in the solar neighborhood -- V. Discovery of coronae of nearby star clusters
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In this paper, we present a novel view on the morphology and the dynamical state of 10 prominent, nearby ($leq$ 500 pc), and young ($sim$30-300 Myr) open star clusters with Gaia DR2: $alpha,$Per, Blanco 1, IC 2602, IC 2391, Messier 39, NGC 2451A, NGC 2516, NGC 2547, Platais 9, and the Pleiades. We introduce a pioneering member identification method that is informed by cluster bulk velocities and deconvolves the spatial distribution with a mixture of Gaussians. Our approach enables inferring the clusters true spatial distribution by effectively filtering field star contaminants while at the same time mitigating the impact of positional errors along the line of sight. This first application of the method reveals the existence of vast stellar coronae, extending for $gtrsim,$100 pc and surrounding the, by comparison tiny and compact, cluster cores. The coronae and cores form intertwined, co-eval, and co-moving extended cluster populations, each encompassing tens of thousands of cubic parsec and stretching across tens of degrees on the sky. Our analysis shows that the coronae are gravitationally unbound but largely comprise the bulk of the populations stellar mass. Most systems are in a highly dynamic state, showing evidence of expansion and sometimes simultaneous contraction along different spatial axes. The velocity field of the extended populations for the cluster cores appears asymmetric but is aligned along a spatial axis unique to each cluster. The overall spatial distribution and the kinematic signature of the populations are largely consistent with the differential rotation pattern of the Milky Way. This finding underlines the important role of global Galactic dynamics to the fate of stellar systems. Our results highlight the complexity of the Milky Ways open cluster population and call for a new perspective on the characterization and dynamical state of open clusters.
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We report the discovery of a young (only 30-40,Myr) snake-like structure (dubbed a stellar snake) in the solar neighborhood from {it Gaia} DR2. The average distance of this structure is about 310,pc from us. Both the length and width are over 200,pc,
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We present medium resolution spectroscopy and multi-epoch VRI photometry for 21 new nearby (< 50 pc) white dwarf systems brighter than V ~ 17. Of the new systems, ten are DA (including a wide double degenerate system with two DA components), eight ar
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We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located within 500 pc of the Sun, using Gaia EDR3 and kinematic data from literature. Members of OCs are identified using the unsupervised machine learning method StarGO, using 5D
parameters (X, Y, Z, $mu_alpha cosdelta, mu_delta$). The OC sample covers an age range of 25Myr--2.65Gyr. We correct the asymmetric distance distribution due to the parallax error using Bayesian inversion. The uncertainty in the corrected distance for a cluster at 500~pc is 3.0--6.3~pc, depending on the intrinsic spatial distribution of its members. We determine the 3D morphology of the OCs in our sample and fit the spatial distribution of stars within the tidal radius in each cluster with an ellipsoid model. The shapes of the OCs are well-described with oblate spheroids (NGC2547, NGC2516, NGC2451A, NGC2451B, NGC2232), prolate spheroids (IC2602, IC4665, NGC2422, Blanco1, Coma Berenices), or triaxial ellipsoids (IC2391, NGC6633, NGC6774). The semi-major axis of the fitted ellipsoid is parallel to the Galactic plane for most clusters. Elongated filament-like substructures are detected in three young clusters (NGC2232, NGC2547, NGC2451B), while tidal-tail-like substructures (tidal tails) are found in older clusters (NGC2516, NGC6633, NGC6774, Blanco1, Coma Berenices). Most clusters may be super-virial and expanding. $N$-body models of rapid gas expulsion with an SFE of $approx 1/3$ are consistent with clusters more massive than $250rm M_odot$, while clusters less massive than 250$rm M_odot$ tend to agree with adiabatic gas expulsion models. Only six OCs (NGC2422, NGC6633, and NGC6774, NGC2232, Blanco1, Coma Berenices) show clear signs of mass segregation.
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