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In this paper, we investigate the spatial structure and dynamical state of the poorly studied old (∼ 4 Gyr) open cluster Trumpler 19 based on reliable cluster members from G a i a -DR3. The DBSCAN clustering algorithm is used to estimate membership probabilities and select likely cluster members in a normalized 5D parametric space. We identify 859 likely cluster members down to G ∼ 20 mag in the field of the cluster. We estimate a cluster radius of R c l ∼ 18 arcmin (13.1 pc) based on the radial distribution of the cluster members. We find that the cluster is deficient in faint and low-mass stars (G > 18.5 mag) and strong mass segregation has taken place within the cluster. We estimate a core radius of R c = 3.0 ± 0.2 arcmin (2.2 ± 0.1 pc) and a tidal radius of R t = 30.7 ± 9.0 arcmin (22.3 ± 6.5 pc) for the cluster. We estimate a concentration parameter of log (R t / R c) ∼ 1.0 , indicating that Trumpler 19 has formed a clear core-halo structure due to dynamical evolution. We investigate the dynamical state of the cluster using 26 blue stragglers (BSs) identified in the cluster. We find that the BSs extend to a radius of ∼ 10.5 arcmin (3.5 R c ), and 16 of them (∼ 62 % ) are located in the core radius of the cluster. We also find that the BSs are significantly more concentrated than the red giant branch (RGB) and main-sequence (MS) stars, indicating that Trumpler 19 is a dynamically old cluster. [ABSTRACT FROM AUTHOR]

This paper revisits fundamental properties of the old open cluster NGC 188 based on more reliable cluster members in G a i a -EDR3. The DBSCAN clustering algorithm is used to identify cluster members in a normalized 5D parametric space. We obtain 1212 core members and 183 border members down to G ∼ 21 mag within 60 arcmin of the cluster center. These 5D cluster members enable us to estimate more precise fundamental parameters for the cluster. The distance of NGC 188 is determined to be 1847 ± 6 pc using a Monte-Carlo simulation method. The lower limit of the cluster radius is estimated to be R c l ∼ 34 arcmin (18.2 pc). We find that NGC 188 has a core radius of R c = 4.5 ± 0.1 arcmin (2.4 ± 0.1 pc) and a tidal radius of R t = 56.3 ± 8.8 arcmin (30.2 ± 4.7 pc), respectively. The concentration parameter of the cluster is determined to be log (R t / R c) ∼ 1.1 , indicating that NGC 188 has formed a dense core and an extended halo due to dynamical evolution. We confirm that the halo of the cluster is slightly asymmetrical. We also investigate the Galactic orbit of the cluster based on the obtained distance and kinematics. We determine a low orbit eccentricity (e ∼ 0.053 ) and a high maximum distance from the Galactic plane ( Z max ∼ 873 pc). The orbit parameters indicate that NGC 188 is a typical thick-disk cluster located well outside the solar circle. [ABSTRACT FROM AUTHOR]

The phenomenon of interaction between planetary nebulae (PNe) and the interstellar medium (ISM) is one of the significant issues in the field of astrophysics. The main objective of this paper is to verify the interaction process for objects that have been known as interacting PNe (IPNe) in the literature. This study is based on parallax and proper motion observations facilitated recently by the early third data release of the Gaia space mission. Based on the proper nebular central star (CS) motion towards the region of interaction between the PN and ISM, we were able to verify the interaction process for a group of 68 PNe and disprove the interaction process for a group of 33 PNe. The members of both groups were confirmed as genuine PN-ISM interacting objects in the literature. The members belonging to the 33 PNe group are false PN-ISM interacting objects that mimic the structure of IPNe. Moreover, we calculated the physical and kinematic properties of the verified group and analyzed their galactic population classification using reliable and precise measurements of the proper motion and parallax of the CS. We find that 41% and 41% of this group are associated with galactic thin and thick disks, respectively, while 18% are members of thin or thick disks. The kinematical results show that the galactic thin-disk members have smaller vertical galactic heights, space velocities, and peculiar velocities than those belonging to the galactic thick disk. [ABSTRACT FROM AUTHOR]

This paper investigates reliable memberships and fundamental astrophysical properties of the old (∼8 Gyr) open cluster NGC 6791 using the astrometric and photometric data of the Gaia data release 2 (Gaia -DR2). We identify 2536 likely cluster members (≥0.6) in a five-dimensional (5D) parameter space using a Gaussian mixture model (GMM) clustering method. Based on these reliable 5D cluster members, we determine the core and tidal radii of the cluster to be R c = 3.69 ′ ± 0.23 ′ and R t = 16.96 ′ ± 2.29 ′ , respectively. We find evidence for the presence of mass segregation in the cluster. Among the likely cluster members, we identify six blue subdwarfs, 43 blue stragglers, and 27 red clump giants. We find that 34 blue stragglers (∼79%) lie within the core radius (< 3.69 ′ ) of the cluster, indicating that these stars may be formed by star collisions or by the evolution of primordial binaries within the dense core. The 27 red clump giants are used to accurately estimate the distance of the cluster. We determine a distance of 4118 ± 23 pc for the cluster using a Monte-Carlo simulation method. We confirm the presence of a significant zero-point offset (∼ − 0.055 ± 0.004 mas) in the Gaia parallaxes of the cluster members. Using the same simulation method, the mean proper motion and radial velocity of the cluster are found to be (〈 μ α cos δ 〉 , 〈 μ δ 〉) = (− 0.434 ± 0.008 , − 2.266 ± 0.010) mas/yr and 〈 V r 〉 = − 46.7 ± 0.6 km/s, respectively. [ABSTRACT FROM AUTHOR]

We calculated the median parallaxes for 47 OB associations including at least 10 stars with known Gaia DR2 parallaxes. A comparison between trigonometric and photometric parallaxes of OB associations reveals a zero-point offset of Δ ϖ = − 0.11 ± 0.04 mas indicating that Gaia DR2 parallaxes are, on average, underestimated and the distances derived from them are overestimated. The correction of Δ ϖ = − 0.11 mas is consistent with the estimate that Arenou et al. (2018) obtained for bright stars. An analysis of parallaxes of OB associations and high-luminosity field stars confirms our previous conclusion (Dambis et al. 2001) that the distance scale for OB stars established by Blaha and Humphreys (1989) must be reduced by 10–20%. Spurious systematic motions of 10–20 km s−1 at the distances of 2–3 kpc from the Sun are found to arise from the use of the uncorrected Gaia DR2 parallaxes. [ABSTRACT FROM AUTHOR]