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In this paper, we investigate the memberships, spatial structure, and dynamical state of the old open cluster Collinder 261 (8 Gyr) based on Gaia-DR3 data. We develop a robust clustering method to calculate membership probabilities for 24858 sample stars within 20′ of the cluster center. We can identify 2619 likely cluster members (including 54 blue stragglers) down to G ∼ 20 mag. We use a Monte Carlo simulation method to estimate a distance of 2909 ± 90 pc for the cluster based on 281 high-probability members (P > 0.9). We find that the detectable cluster radius (R cl) is at least 14′ (∼11.8 pc), which is much larger than previously thought. Based on the obtained cluster members, the core and tidal radii of the cluster are determined to be |$R_{\rm c}={3{^{\prime }_{.}}4}\pm {0.1}$| (∼2.9 ± 0.1 pc) and |$R_{\rm t}={19{^{\prime }_{.}}8}\pm {1{^{\prime }_{.}}9}$| (∼16.8 ± 1.6 pc), respectively. A concentration parameter of log (R t/ R c) ∼0.76 is determined, indicating that Collinder 261 has formed a clear core–halo structure, but its spatial structure is much looser than the old open clusters M 67 (4 Gyr) and NGC 188 (7 Gyr). We also find that the membership probabilities are suitable for analyzing the mass segregation effect in the cluster. The orbit parameters show that Collinder 261 is moving along a near-circular orbit (e ∼ 0.025) well inside the solar circle (R p ∼ 6.928 kpc, R a ∼ 7.285 kpc), and it can reach a maximum height of Z max ∼ 533 pc from the Galactic plane. [ABSTRACT FROM AUTHOR]

We conducted astrometry of H2O masers in Galactic star-forming regions G48.99-0.30 and G49.19-0.34 with VLBI Exploration of Radio Astrometry (VERA). The observational results yield the parallaxes of G48.99-0.30 and G49.19-0.34 to be 0.178±0.017 mas (5.62+0.59-0.49 kpc) and 0.211±0.016 mas (4.74+0.39-0.33 kpc), respectively. We discuss in detail the sources of astrometric errors based on the observations of the two sources. The positional systemic errors in RA and Dec of (23, 31)μ as for G49.19-0.34 are dominated by a tropospheric contribution from the Earth's atmosphere. Those of (23, 53)μas for G48.99-0.30 are attributed to a tropospheric contribution and a maser structure effect. The formal positional error from thermal noise is significantly smaller than these systemic positional errors. VERA phase-referencing observations could achieve a positional accuracy of a few tens of μas in both RA and Dec directions for point-like and bright sources at high elevation. [ABSTRACT FROM AUTHOR]

We performed astrometric observations of IRAS 20126+4104 with the very long baseline interferometry (VLBI) Exploration of Radio Astrometry (VERA). The measured parallax was 0.750±0.092 mas, corresponding to a distance of 1.33+0.19 -0.15 kpc. We found that IRAS 20126+4104 is located approximately 100 pc above the Galactic plane and moving further away from the Galactic plane with a velocity of approximately 16±4kms-1. This motion would be associated by common origin with the expanding motions of OB typestars in the Cygnus superbubble. [ABSTRACT FROM AUTHOR]

As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151 ± 0.042 mas, which corresponds to a distance of |$D = 6.61^{+2.55}_{-1.44}\:{\rm kpc}$|⁠ , and the obtained proper motion components were |$(\mu _\alpha {\rm cos}\delta ,\, \mu _\delta) = (-1.44 \pm 0.15,\, -0.27 \pm 0.16)\:{\rm mas\:yr^{-1}}$| in equatorial coordinates. Assuming Galactic constants of |$(R_0,\, \Theta _0) = (8.05 \pm 0.45\:{\rm kpc},\, 238 \pm 14\:{\rm km\:s^{-1}})$|⁠ , the Galactocentric distance and rotation velocity were measured to be |$(R,\, \Theta) = (13.04 \pm 2.24\:{\rm kpc},\, 239 \pm 22\:{\rm km\:s^{-1}})$|⁠ , which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, |$L_{\rm Bol} = (3.11 \pm 2.86) \times 10^{3}\, L_{\odot }$|⁠ , which corresponds to a spectral type of B1–B2. Analysis of |${}^{12}{\rm{CO}}$| (J = 1–0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which matches well a structure predicted by numerical simulation of the cloud–cloud collision phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of the two initial clouds was as slow as 3– |$5\:{\rm km\, s^{-1}}$|⁠ , which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (∼3–5 km s−1), as suggested by Takahira, Tasker, and Habe (2014 , ApJ, 792, 63). [ABSTRACT FROM AUTHOR]

Highlights from the article: 23508 and 17694 sample stars for NGC 2281 and NGC The distances of NGC 2281 and NGC 2539 are D = We find that NGC 2811 and NGC 2539 have 42 Methods: data analysis, methods: statistical, open clusters and associations: individual (NGC 2281, NGC 2539), parallaxes, proper motions.