We present a catalogue of candidates in extragalactic objects -- the Northern Extragalactic WISExPan-STARRS (NEWS), which covers almost 3/4 of the sky in a broad optical-infrared spectral range, with a depth of up to 23mag in optical filter g. To create the NEWS catalogue, we used the mid-IR data of the WISE survey (W1,W2) paired up with photometric information of the Pan-STARRS DR1 survey in the optical and near-IR (g,r,i,z,y) spectral ranges. Our catalogue is the result of a classification of the WISExPan-STARRS objects with the SVM machine-learning algorithm. The classification was based solely on photometric information and the automatic creation of features that was carried out using an autoencoder neural network. NEWS catalogue contains 40,350,492 extragalactic objects (galaxies and quasars), identified with a high classification quality (>98%).
The present high accuracy of stellar positions and proper motions allows us to determine the positional accuracy of old stellar catalogues. This has already been done for the most important catalogues from before the 18th century. Our aim is to extend this study to several 18th century catalogues. To do this, I studied ten catalogues: those of Flamsteed and Romer, four catalogues of La Caille, and catalogues of Tobias Mayer, Bradley, Piazzi, and Lalande. A comparison with modern data, mostly from Hipparcos, compiled in the Simbad data base of the CDS allowed me to determine the position errors of these catalogues. I also compared the stellar visual magnitudes given in eight of these catalogues with photometric V magnitudes. Thanks to novel instruments, the r.m.s. positional accuracy improved from thousands to hundreds of arc seconds in older catalogues to less than one minute in that of Flamsteed, and to 2-6 arcseconds in the other catalogues I examined. These improvements allowed for the first time relatively accurate proper motions to be determined by 19th century astronomers.
NGC 2548 is a ~400-500Myr old open cluster with evidence of spatial substructures likely caused by its interaction with the Galactic disc. In this work we use precise astrometric data from the Carte du Ciel - San Fernando (CdC-SF) catalogue to study the clumpy structure in this cluster. We confirm the fragmented structure of NGC 2548 but, additionally, the relatively high precision of our kinematic data lead us to the first detection of substructures in the proper motion space of a stellar cluster. There are three spatially separated cores each of which has its own counterpart in the proper motion distribution. The two main cores lie nearly parallel to the Galactic plane whereas the third one is significantly fainter than the others and it moves towards the Galactic plane separating from the rest of the cluster. We derive core positions and proper motions, as well as the stars belonging to each core.
The halos of elliptical galaxies are faint and difficult to explore, but they contain vital clues to both structure and formation. We present the results of an imaging and spectroscopic survey for planetary nebulae (PNe) in the nearby elliptical NGC 5128. We extend the work of Hui and coworkers (Cat. <J/ApJ/449/592>) well into the halo of the galaxy - out to distances of 100 and 50kpc along the major and minor axes. We now know of 1141 PNe in NGC 5128, 780 of which are confirmed. Of these 780 PNe, 349 are new from this survey, and 148 are at radii beyond 20kpc. PNe exist at distances up to 80kpc (~15r_e_), showing that the stellar halo extends to the limit of our data.
This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8Gyr and masses close to the canonical 0.6M_{sun}_.
The Naval Observatory Merged Astrometric Dataset (NOMAD) contains astrometric and photometric data for over 1 billion stars derived from the Hipparcos (I/239), Tycho-2 (I/259), UCAC2 (I/289), and USNO-B1.0 (I/284) catalogs for astrometry and optical photometry, supplemented by 2MASS (II/246) near-infrared photometry. For each unique star the "best" astrometric and photometric data are chosen from the source catalogs and merged into a single dataset. A sequence of priorities is followed and NOMAD contains flags to identify the source catalogs and gives cross-reference identifications. This first release of NOMAD is not a compiled catalog; that is, if a star is identified in more than 1 of the above mentioned catalogs, only 1 catalog entry is chosen. Thus the local and global systematic errors of the various source catalogs will be present in this version of NOMAD. All source catalogs astrometric data are on the International Celestial Reference System within the limitations of the source catalogs. For more information, see https://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/nomad A dedicated remote query program can be downloaded from http://cdsweb.u-strasbg.fr/doc/cdsclient.html
In this article we study the N83-84-85 region of the inner wing of the SMC. Direct and low-dispersion objective prism plates taken with the 1.2m UK Schmidt Telescope have been digitized by the SuperCOSMOS machine. Star counts have been performed for our region in selected luminosity slices in the U filter and isodensity contours have been used to identify the structures with enhanced stellar number density. We find evidence of triggered star formation from massive stars of older to more recent OB associations. Circular arcs constructed by O and B stars have been detected. A study of the population places stars with more recent ages in the groups of the arcs than of their centers. These effects can be explained by supernova explosions. A catalogue of the non-saturated detected OB stars in this region is given.
Results of observations of the Galilean moons of Jupiter were carried out at the Normal Astrograph of the Pulkovo Observatory in 2018. We obtained 452 positions of the Galilean moons of Jupiter in the Gaia DR1 catalog system (ICRF, J2000.0) and 671 differential coordinates of the satellites relative to each other. The obtained mean errors in the satellites normal positions on the right ascension and declination, which demonstrate the intrinsic convergence of the observational results, are (eps)RA=0.003" and (eps)DE= 0.003", respectively, for the entire observational period. The errors of one difference are (sigm)RA=0.070", and (sigm)DE=0.067",respectively. The equatorial coordinates of the moons were compared to eight motion theories of planets and satellites. On average, the (O.C) residuals in the both coordinates relative to the motion theories are 0.014". The best agreement with observations is achieved by combination of all four motion theories of satellites with the planetary theory EPM2017, which yields average (O-C) residuals of approximately 0.01" for each of them. The new results were compared to those of the 2016-2017 observational season. As in the past, peculiarities in the behavior of the (O-C) residuals for Io and Ganymede have been noticed.
The prediction of stellar occultations by trans-Neptunian objects (TNOs) and Centaurs is a difficult challenge that requires accuracy both in the occulted star position and in the object ephemeris. Until now, the most used method of prediction, involving dozens of TNOs/Centaurs, has been to consider a constant offset for the right ascension and for the declination with respect to a reference ephemeris, usually the latest public version. This offset is determined as the difference between the most recent observations of the TNO/Centaur and the reference ephemeris. This method can be successfully applied when the offset remains constant with time, i.e. when the orbit is stable enough. In this case, the prediction even holds for occultations that occur several days after the last observations. This paper presents an alternative method of prediction, based on a new accurate orbit determination procedure, which uses all the available positions of the TNO from the Minor Planet Center database, as well as sets of new astrometric positions from unpublished observations. Orbits were determined through a numerical integration procedure called NIMA, in which we developed a specific weighting scheme that considers the individual precision of the observation, the number of observations performed during one night by the same observatory, and the presence of systematic errors in the positions.
Astrometric positions of the Neptunian Satellite Triton are given for the opposition of Neptune for the years 1996, 2003, 2005 and 2006. The 943 observed positions were obtained at the Cassegrain focus of a 156-cm reflector. In our reduction, the up-to-date catalogue of stars UCAC2 was chosen to ensure a proper astrometric calibration. Our observed positions are compared to theoretical positions provided from JPL and IMCCE ephemerides. The observed minus calculated residuals have s.d. values of the order of 0.04arcsec.
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