The Distribution of Open Clusters in the Galaxy

In this work we explore the new catalog of galactic open clusters that became available recently, containing 1,750 clusters that have been re-analyzed using the Gaia DR2 catalog to determine the stellar memberships. We used the young open clusters as tracers of spiral arms and determined the spiral pattern rotation speed of the Galaxy and the corotation radius, the strongest Galactic resonance. The sample of open clusters used here is increased by dozens of objects with respect to our previous works. In addition, the distances and ages values are better determined, using improvements to isochrone fitting and including an updated extinction polynomial for the Gaia DR2 photometric band-passes, and the Galactic abundance gradient as a prior for metallicity. In addition to the better age determinations, the catalog contains better positions in the Galactic plane and better proper motions. This allow us to discuss not only the present space distribution of the clusters, but also the space distribution of the clusters's birthplaces, obtained by integration of the orbits for a time equal to their age. The value of the rotation velocity of the arms (28.5 ± 1.0 km s−1 kpc−1) implies that the corotation radius (Rc) is close to the solar Galactic orbit (Rc/R0 = 1.01±0.08), which is supported by other observational evidence discussed in this text. A simulation is presented, illustrating the motion of the clusters in the reference frame of corotation. We also present general statistics of the catalog of clusters, like spatial distribution, distribution relative to height from the Galactic plane, and distribution of ages and metallicity. An important feature of the space distribution, the corotation gap in the gas distribution and its consequences for the young clusters, is discussed.

Annual parallax and galactic orbit of Y Librae (IRAS 15090−0549) Mira variable star—GALORB release

Using the VLBI Exploration of Radio Astrometry (VERA), we measured the trigonometric parallax of an H2O maser source in a variable star of Mira Cet type, Y Lib, to be 0.855 ± 0.050 mas, corresponding to a distance of 1.17 ± 0.07 kpc. From multi-epoch infrared observations with the Kagoshima University 1 m telescope, we derived the mean J, H, and K′-band magnitudes of Y Lib to be 4.34 ± 0.22 mag, 3.62 ± 0.18 mag, and 3.25 ± 0.16 mag, respectively. The pulsation period of Y Lib was obtained to be 277.2 ± 13.9 d. We derived the effective temperature and radius of Y Lib to be 3100 ± 125 K and $211 \pm 11 \, R_{\odot }$, respectively. The peculiar motion of Y Lib Us (motion towards the Galactic center), Vs (motion in the direction of Galactic rotation), and Ws (motion towards the Galactic North Pole) were obtained to be −16 ± 3 km s−1, 25 ± 2 km s−1, and 13 ± 3 km s−1, respectively. After validation, we used the new release of the GALactic ORbit simulation package to trace the past 1 Gyr orbit of Y Lib in the Milky Way. Fitting the orbit of Y Lib with the MWPotential2014 Galactic Potential model produced high eccentricity in the direction perpendicular to the Galactic center, but decreasing the Miyamoto–Nagai disk potential contribution in the Milky Way model produced a reasonable result of the Y Lib orbit.

Thousands of Stellar SiO masers in the Galactic center: The Bulge Asymmetries and Dynamic Evolution (BAaDE) survey

A radio survey of red giant SiO sources in the inner Galaxy and bulge is not hindered by extinction. Accurate stellar velocities (<1 km/s) are obtained with minimal observing time (<1 min) per source. Detecting over 20,000 SiO maser sources yields data comparable to optical surveys with the additional strength of a much more thorough coverage of the highly obscured inner Galaxy. Modeling of such a large sample would reveal dynamical structures and minority populations; the velocity structure can be compared to kinematic structures seen in molecular gas, complex orbit structure in the bar, or stellar streams resulting from recently infallen systems. Our Bulge Asymmetries and Dynamic Evolution (BAaDE) survey yields bright SiO masers suitable for follow-up Galactic orbit and parallax determination using VLBI.Here we outline our early VLA observations at 43 GHz in the northern bulge and Galactic plane (0<l°<250), and ALMA observations at 86 GHz in the southern bulge (250<l°<360). We report a preliminary overall 70% detection rate in our color-selected MSX sources.

Tidal Tails of the Nearest Open Clusters

We show that an extended population of stars escaping an evolved cluster and moving along its galactic orbit forms at the final phases of its dynamical evolution. Here we present some results of the numerical simulations for nearest open clusters: Hyades, Pleiades, Praesepe, Alpha Persei, Coma, IC 2391, and IC 2602. We calculated the models of the stellar tails for nearest open clusters and estimated some parameters: sizes, densities, locations relative to the solar neighborhood. Stars of the nearest tails can be observed as moving clusters.

The Local Galactic Escape Velocity

We discuss the corrections to the perceived motions of stars due to the disk’s circular velocity, which we determine to be 220 km sec . This implies a Keplerian escape velocity of 310 km sec−1. We discuss upper limits to the rest-frame space velocities of stars from four sources: the summary of Saio and Yoshii (1979); the large new survey of proper motion stars of Carney and Latham (1985); a study of 27 faint proper motion stars near the South Galactic Pole by Carney and Peterson (1984a); and observations by Carney and Peterson (1984b) of stars with possibly extreme velocities identified by Eggen (1969). We find the maximum velocities are near 500 km secc−1, which is likely to be the local value of the escape velocity. This implies a large amount of gravitating matter outside the solar galactic orbit.