3D IMAGE OF POLARIS FIELD STARS

Astronomers are entering an era of {\mu}as-level astrometry utilizing the 5-decade-old IAU Galactic coordinate system that was only originally defined to $\sim$0{\deg}.1 accuracy, and where the dynamical centre of the Galaxy (Sgr A*) is located $\sim$0{\deg}.07 from the origin. We calculate new independent estimates of the North Galactic Pole (NGP) using recent catalogues of Galactic disc tracer objects such as embedded and open clusters, infrared bubbles, dark clouds, and young massive stars. Using these catalogues, we provide two new estimates of the NGP. Solution 1 is an "unconstrained" NGP determined by the galactic tracer sources, which does not take into account the location of Sgr A*, and which lies 90{\deg}.120$\,\pm\,$0{\deg}.029 from Sgr A*, and Solution 2 is a "constrained" NGP which lies exactly 90{\deg} from Sgr A*. The "unconstrained" NGP has ICRS position: $\alpha_{NGP}$ = 192{\deg}.729 $\,\pm\,$ 0{\deg}.035, $\delta_{NGP}$ = 27{\deg}.084 $\,\pm\,$ 0{\deg}.023 and $\theta\,$ = 122{\deg}.928 $\,\pm\,$ 0{\deg}.016. The "constrained" NGP which lies exactly 90{\deg} away from Sgr A* has ICRS position: $\alpha_{NGP}$ = 192{\deg}.728 $\,\pm\,$0{\deg}.010, $\delta_{NGP}$ = 26{\deg}.863 $\,\pm\,$ 0{\deg}.019 and $\theta\,$ = 122{\deg}.928 $\,\pm\,$ 0{\deg}.016. The difference between the solutions is likely due to the Sun lying above the Galactic midplane. Considering the angular separation between Sgr A* and our unconstrained NGP, and if one adopts the recent estimate of the Galactocentric distance for the Sun of $R_{0}$ = 8.2$\,\pm\,$0.1 kpc, then we estimate that the Sun lies $z_{\odot}$ $\simeq$ 17$\,\pm\,$5 pc above the Galactic midplane. Our value of $z_{\odot}$ is consistent with the true median of 55 previous estimates published over the past century of the Sun's height above the Galactic mid-plane ($z_{\odot}$ $\simeq$ 17$\,\pm\,$2 pc).

Background. The current stage of aviation development is characterized by a steady tendency to increase requirements for the tactical and technical characteristics of aircraft, including navigation systems. A natural consequence of this tendency is the increasing role and importance of radar sensors of navigation information. These include radio altimeter systems (RAS), which measure the altitude and components of the velocity vector in a linked coordinate system. At present, an urgent task is to improve the accuracy of RAS characteristics over heterogeneous complex surfaces. Materials and methods. Considers the following methods for solving the problem: adaptation of algorithms for estimating the components of the RAS velocity vector to the underlying surface by changing the pulses time depending on the value of the aircraft flight altitude; adaptation of algorithms for estimating the components of the RAS velocity vector to the underlying surface by changing the antenna system configuration; adaptation of algorithms for estimating the components of the RAS velocity vector to the underlying surface by switching the RAS frequency. Results and conclusions. Methods usage will significantly improve the tactical and technical characteristics of both existing RAS and new developments, and will reduce the time of development.

view Abstract Citations (172) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The distribution of stars to V = 16th magnitude near the north galactic pole - Normalization, clustering properties, and counts in various bands. Bahcall, J. N. ; Soneira, R. M. Abstract The distribution on the sky of stars brighter than V= 16 mag near the North Galactic Pole is discussed. The available data are reviewed; the most important new data are from the catalog of Weistrop. All of the data are in agreement with predictions made from our standard Galaxy model when the giants are treated separately from the main sequence stars. Transformations between different photometric bands, including U, B, J, F, V, R, I, g, and r, are given for a wide range of stellar types and luminosity classes. The necessary ingredients are provided for making color transformations to arbitrary bands that may be defined in the future with characteristic wavelengths between 4000 and 8500 A. Some illustrative applications are made to bands that are defined for Space Telescope instruments. The star counts are predicted in all of the above listed bands down to 16th magnitude using the data of Weistrop with the color corrections of Faber et al. The clustering properties of the stars are investigated with the aid of the two-point correlation function and the distributions of first and second-nearest neighbors, as well as photometric parallaxes. A significant fraction (∼15%) of the stars appear to be in binaries or triplets with a typical separation of order 0.1 pc. Publication: The Astrophysical Journal Pub Date: May 1981 DOI: 10.1086/158905 Bibcode: 1981ApJ...246..122B Keywords: Astronomical Photometry; Binary Stars; Star Clusters; Star Distribution; Stellar Luminosity; Stellar Magnitude; Stellar Parallax; Astrophysics full text sources ADS | data products SIMBAD (38)

The definition of the Galactic coordinate system was announced by the IAU Sub-Commission 33b on behalf of the IAU in 1958. For more than 50 years the definition of the Galactic coordinate system has remained unchanged from this IAU1958 version. On the basis of deep and all-sky catalogs, the position of the Galactic plane can be revised and updated definitions of the Galactic coordinate systems can be proposed. We re-determine the position of the Galactic plane based on modern large catalogs, such as the Two Micron All-Sky Survey (2MASS) and the SPECFIND v2.0. This paper also aims to propose a possible definition of the optimal Galactic coordinate system by adopting the ICRS position of the Sgr A* at the Galactic center. The near-infrared 2MASS point source catalog and the SPECFIND v2.0 catalog of radio continuum spectra are used to determine the mean position of the Galactic plane on the celestial sphere. By fitting the data to an ideal Galactic equator, the parameters defining the Galactic coordinate system are obtained. We find that the obliquity of the Galactic equator on the ICRS principal plane is about $0.4^\circ$ (2MASS) and $0.6^\circ$ (SPECFIND v2.0) larger than the J2000.0 value, which is widely used in coordinate transformations between the equatorial $(\alpha, \delta)$ and the Galactic $(\ell, b)$. Depending on the adopted parameters, data, and methods, the largest difference between the resulting Galactic coordinate systems is several arcminutes. We derive revised transformation matrices and parameters describing the orientation of the Galactic coordinate systems in the ICRS at the 1 milli-arcsecond level to match the precision of modern observations. For practical applications, we propose that a revised definition of the Galactic coordinate system should be required in the near future.

The currently used Galactic coordinate system (GalCS) is based on the FK5 system at J2000.0, which was transformed from the FK4 system at B1950.0. The limitations and misunderstandings related to this transformed GalCS can be avoided by defining a new GalCS that is directly connected to the International Celestial Reference System (ICRS). With more data at various wavelengths released by large survey programs, a more appropriate GalCS consistent with features associated with the Milky Way can be established. We try to find the best orientation of the GalCS using data from two all-sky surveys, AKARI and WISE, at six wavelengths between 3.4 μm and 90 μm, and synthesize results obtained at various wavelengths to define an improved GalCS in the framework of the ICRS. The revised GalCS parameters for defining the new GalCS in the ICRS are summarized as: αp = 192.777°, δp = 26.9298°, for the equatorial coordinates of the north Galactic pole and θ = 122.95017° for the position angle of the Galactic center. As one of the Galactic substructures, the Galactic warp exhibits different forms in different GalCSs that are constructed with various data and methods, which shows the importance of re-defining the GalCS by the relative commission of the International Astronomical Union that can lead to a better understanding of Galactic structure and kinematics.

Gaia BHs, black hole (BH) binaries discovered from data base of an astrometric telescope Gaia, pose a question to the standard binary evolution model. We have assessed whether Gaia BHs can be formed through dynamical capture in open clusters rather than through isolated binary evolution. We have performed gravitational N-body simulations of 100 open clusters with $10^5 \, \mathrm{M}_\odot$ in total for each metallicity Z = 0.02, 0.01, and 0.005. We have discovered one Gaia BH-like binary escaping from an open cluster, and found that the formation efficiency of Gaia BHs in open clusters ($\sim 10^{-5} \, \mathrm{M}_\odot ^{-1}$) is larger than in isolated binaries ($\sim 10^{-8} \, \mathrm{M}_\odot ^{-1}$) by 3 orders of magnitude. The Gaia BH-like binary is the inner binary of a triple star system. Gaia BHs can have tertiary stars frequently, if they are formed in open clusters. Combining additional N-body simulations with 8000 open clusters with $8 \times 10^6 \, \mathrm{M}_\odot$, we have estimated the number of Gaia BHs in the Milky Way disc to 104–105 (depending on the definitions of Gaia BHs), large enough for the number of Gaia BHs discovered so far. Our results indicate that the discoveries of Gaia BHs do not request the reconstruction of the standard binary evolution model, and that Gaia BHs are a probe for the dynamics of open clusters already evaporated.

We assess the accuracy of radial velocities of 671 stars located near Galactic clusters, measured by Robert Trumpler between 1924 and 1947 using the Lick Observatory 36 inch refractor equipped with prism spectrometers and photographic plates. We find that Trumpler’s velocities share the same zero-point and scale as modern IAU radial velocity standards. Their accuracy ranges from 2 to 7 km s−1, depending on stellar brightness, based on comparisons with new Doppler measurements from the Keck telescope and data from SIMBAD. We also provide improved star identifications, B-band photometry, and notes. A link is provided to an online PDF—previously available only in print—containing all 3782 of Trumpler’s stellar radial velocities and associated Julian dates. These historical data can be combined with modern measurements to form a unique century-long baseline for detecting long-period stellar companions, gravitational perturbations from passing massive objects, and accelerations due to cluster and Galactic dynamics.

Context. The properties of open clusters such as metallicity, age, and morphology are useful tools in studies of the dynamic evolution of open clusters. The morphology of open clusters can help us better understand the evolution of such structures. Aims. We aim to analyze the morphological evolution of 1256 open clusters by combining the shapes of the sample clusters in the proper motion space with their morphology in the two-dimensional spherical Galactic coordinate system, providing their shape parameters based on a member catalog derived from Gaia Second Data Release as well as data from the literature. Methods. We applied a combination of a nonparametric bivariate density estimation with the least square ellipse fitting to derive the shape parameters of the sample clusters. Results. We derived the shape parameters of the sample clusters in the two-dimensional spherical Galactic coordinate system and that of the proper motion space. By analyzing the dislocation of the sample clusters, we find that the dislocation, d, is related to the X-axis pointing toward the Galactic center, Y-axis pointing in the direction of Galactic rotation, and the Z-axis (log(|H|/pc)) that is positive toward the Galactic north pole. This finding underlines the important role of the dislocation of clusters in tracking the external environment of the Milky Way. The orientation (qpm) of the clusters, with epm ≥ 0.4, presents an aggregate distribution in the range of −45° to 45°, comprising about 74% of them. This probably suggests that these clusters tend to deform heavily in the direction of the Galactic plane. NGC 752 is in a slight stage of expansion in the two-dimensional space and will become deformed, in terms of its morphology, along the direction perpendicular to the original stretching direction in the future if no other events occur. The relative degree of deformation of the sample clusters in the short-axis direction decreases as their ages increase. On average, the severely distorted sample clusters in each group account for about 26% ± 9%. This possibly implies a uniform external environment in the range of |H| ≤ 300 pc if the sample completeness of each group is not taken into account.

This work numerically simulates fracture flow in natural fractures, specifically in a joint with plumose pattern. A natural fracture surface, previously measured in the field using LiDAR scanning, was used to rebuild an open fracture geometry, assuming mode 1 fracture opening. Three-dimensional fracture flow was modeled by solving Stokes equation in a stationary regime using the finite element method. Three different pressure gradients and apertures were numerically investigated to better understand the impact of plumose patterns with different degrees of roughness. Resulting fracture flow fields were characterized by hydraulic aperture and by statistics on the directional components of the three-dimensional velocity vector. The results show that the hydraulic aperture and the longitudinal component of the velocity vector decrease with increasing roughness. Beyond this classical finding, the study shows that the variance of the longitudinal component of the flow velocity vector also decreases with increasing roughness. This behavior can be predicted based on variance estimates connected to the parabolic profile. The results further revealed that the variances of the transverse components of the velocity vector increase with fracture surface roughness. These findings suggest that the roughness-induced reduction in the mean and the variance of the longitudinal component of the velocity vector in joints with rough surfaces is accompanied with a simultaneous increase of the transverse components of the three-dimensional velocity vector.

Initially defined by the IAU in 1958, the galactic coordinate system was\nthereafter in 1984 transformed from the B1950.0 FK4-based system to the J2000.0\nFK5-based system. In 1994, the IAU recommended that the dynamical reference\nsystem FK5 be replaced by the ICRS, which is a kinematical non-rotating system\ndefined by a set of remote radio sources. However the definition of the\ngalactic coordinate system was not updated. We consider that the present\ngalactic coordinates may be problematic due to the unrigorous transformation\nmethod from the FK4 to the FK5, and due to the non-inertiality of the FK5\nsystem with respect to the ICRS. This has led to some confusions in\napplications of the galactic coordinates. We tried to find the transformation\nmatrix in the framework of the ICRS after carefully investigating the\ndefinition of the galactic coordinate system and transformation procedures,\nhowever we could not find a satisfactory galactic coordinate system that is\nconnected steadily to the ICRS. To avoid unnecessary misunderstandings, we\nsuggest to re-consider the definition of the galactic coordinate system which\nshould be directly connected with the ICRS for high precise observation at\nmicro-arcsecond level.\n

The small orbiting observatory MOUSE is described in its essential features. Insights in the optical solution (a 2 mirrors 3 reflections telescope using pure hyperbolical surfaces, no aspherics) are given which fit such type of optical layout to scientific requirements. An in-flight recentering of the photons collected by a solar-blind photon counter device will allow for an equivalent angular resolution of 2-3 arcsec over a field-of-view exceeding one square degree. The capabilities of the proposed satellite (imaging, low resolution grisms, polarizers) are described. The choice of the selected sky areas (the two Galactic Poles, the galactic equator and some Bulge Windows) is justified in terms of forefront astrophysical scientific objectives requiring imaging in UV over large fields. The science comprises UV analysis of a complete sample of QSOs, stellar population in galaxies, White Dwarfs, Globular and Open Clusters and OB Associations. In addition a plan for the early UV detection of Supernova events is described.

\n Context. The global survey of star clusters in the Milky Way (MWSC) is a comprehensive list of 3061 objects that provides, among other parameters, distances to clusters based on isochrone fitting. The Tycho-Gaia Astrometric Solution (TGAS) catalogue, which is a part of Gaia data release 1 (Gaia DR1), delivers accurate trigonometric parallax measurements for more than 2 million stars, including those in star clusters.\n Aims. We compare the open cluster photometric distance scale with the measurements given by the trigonometric parallaxes from TGAS to evaluate the consistency between these values.\n Methods. The average parallaxes of probable cluster members available in TGAS provide the trigonometric distance scale of open clusters, while the photometric scale is given by the distances published in the MWSC. Sixty-four clusters are suited for comparison as they have more than 16 probable members with parallax measurements in TGAS. We computed the average parallaxes of the probable members and compared these to the photometric parallaxes derived within the MWSC.\n Results. We find a good agreement between the trigonometric TGAS-based and the photometric MWSC-based distance scales of open clusters, which for distances less than 2.3 kpc coincide at a level of about 0.1 mas with no dependence on the distance. If at all, there is a slight systematic offset along the Galactic equator between 30° and 160° galactic longitude. \n

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Brightest Stars in Open Clusters. Buscombe, William Abstract Johnson and others have shown that photoelectric photometry in three colors is necessary before accurate distances can be derived for galactic clusters, with proper allowance for interstellar reddening. It is found that the absolute magnitude of a cluster, based on its brightness over the area of sky subtended, is an important parameter for classification. The 150 clusters with photometric parallaxes have been grouped in seven groups of absolute photographic magnitude. A high degree of correlation is noted between the luminosity parameter for a cluster and the MK type of its brightest star. Due to observational selection, the average distance to which clusters have been surveyed declines steadily with their total luminosity. A similar decline in the mean linear di~meter indicates that angular diameter alone is not reliable for estimation of the distance of a cluster, unless other information on the type of cluster is available. Publication: The Astronomical Journal Pub Date: September 1963 DOI: 10.1086/109072 Bibcode: 1963AJ.....68R..70B full text sources ADS |

The distributions of meteor substance in the Galactic coordinate system according to the MARS radar database and SonotaCo's TV catalogue

Using the Gaia DR3 data sets, this work gives an analysis of nine open clusters: Dolidze 25, Kronberger 13, Kronberger 18, Majaess 99, NGC 7795, Ruprecht 139, Teutsch 55, S1, and FSR 0596, which are close to the Galactic plane of the Milky Way. The number of probable cluster members is found to be 81, 77, 120, 155, 108, 110, 160, and 116 respectively. Radii are determined as 5.40, 5.25, 4.80, 4.20, 4.28, 3.70, 4.30, 4.30, and 3.53 arcmin, respectively. With solar metallicity isochrones log ages of 7.70, 9.00, 8.35, 7.50, 9.00, 8.00, 7.50, 8.50, and 9.5 yr are determined for these clusters. The best fitting of the isochrone produced distances of 2.6, 1.27, 1.16, 1.16, 3.10, 1.64, 2.50, 2.44, and 0.98 kpc that are similar to the distances calculated from inverting median parallaxes. The mass function slopes are in agreement with the Salpeter value. The results of the total masses are found to be 116.07, 79.33, 141.24, 147.34, 145.76, 491.01, 155, 212.46, and 82.79 M☉.