New astrometric reductions of the US Naval Observatory CCD Astrograph Catalog (UCAC) all-sky observations were performed from first principles using the TGAS stars in the 8 to 11 magnitude range as reference star catalog. Significant improvements in the astrometric solutions were obtained and the UCAC5 catalog of mean positions at a mean epoch near 2001 was generated. By combining UCAC5 with Gaia DR1 data new proper motions on the Gaia coordinate system for over 107 million stars were obtained with typical accuracies of 1 to 2mas/yr (R=11 to 15mag), and about 5mas/yr at 16th mag. Proper motions of most TGAS stars are improved over their Gaia data and the precision level of TGAS proper motions is extended to many millions more, fainter stars. External comparisons were made using stellar cluster fields and extragalactic sources. The TGAS data allow us to derive the limiting precision of the UCAC x, y data, which is significantly better than 1/100 pixel.
The U.S. Naval Observatory is in the process of making new reductions of the Astrographic Catalogue (AC) using a modern reference system, the ACRS, which represents the system of the FK5. The data from the Uccle Zone, whose plates are centered between declinations +34 and +35 degrees (eq. 1900), have been analyzed for scale, rotation, tilt, coma, magnitude equation, radial distortion and distortions introduced by the use of reseaux in the Carte du Ciel program. The result is a positional catalog of over 117,000 stars on eq. J2000.0, epoch of observation. Additionally, all stars have been matched with the Tycho Input Catalog (revised); those numbers have been added for additional identification purposes.
The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources. The resulting Hertzsprung-Russel diagram reveals fine structures throughout the mass range. This paper aims to investigate the content of Gaia DR2 at the low-mass end and to characterize ultra-cool and brown dwarfs. We first retrieved the sample of spectroscopically confirmed ultra-cool and brown dwarfs in Gaia DR2.We used their locus in the precise Hertzsprung-Russel diagram to select new candidates and to investigate their properties. The number of spectroscopically confirmed objects recovered in Gaia DR2 corresponds to 61% and 74% of the expected number of objects with an estimated Gaia magnitude G_est_<=21.5 and 20.3, respectively. This fills much of the gap to Gaia DR1. Furthermore, Gaia DR2 contains ~13000>=M7 and 631 new L candidates. A tentative classification suggests that a few hundred of them are young or subdwarf candidates. Their distance distribution shows that the solar neighborhood census is still incomplete. Conclusions. Gaia DR2 offers a great wealth of information on low-mass objects. It provides a homogeneous and precise catalog of candidates that is worthwhile to be further characterized with spectroscopic observations.
The catalog of hierarchical stellar systems with three or more components is an update of the original 1997 version (Tokovinin, 1997-1999, J/A+AS/124/75). For 2000 hierarchies, the new Multiple Star Catalog (MSC) provides distances, component masses and periods, and supplementary information (astrometry, photometry, identifiers, orbits, notes). The MSC content and format are explained, and its incompleteness and strong observational selection are stressed. Nevertheless, the MSC can be used for statistical studies and is a valuable source for planning observations of multiple stars. Rare classes of stellar hierarchies found in the MSC (with six or seven components, extremely eccentric orbits, planar and possibly resonant orbits, hosting planets) are briefly presented. High-order hierarchies have smaller velocity dispersion compared to triples and are often associated with moving groups. The paper concludes with an analysis of the ratio of periods and separations between inner and outer subsystems. In wide hierarchies, the ratio of semimajor axes, estimated statistically, is distributed between 3 and 300, with no evidence of dynamically unstable systems.
We have used high-cadence radial velocity (RV) measurements from the Hobby-Eberly Telescope with existing velocities from the Lick, Elodie, Harlan J. Smith, and Whipple 60" telescopes combined with astrometric data from the Hubble Space Telescope Fine Guidance Sensors to refine the orbital parameters and determine the orbital inclinations and position angles of the ascending node of components {upsilon} And A c and d. With these inclinations and using M*=1.31M_{sun}_ as a primary mass, we determine the actual masses of two of the companions: {upsilon} And A c is 13.98^+2.3^_-5.3_M_Jup_, and {upsilon} And A d is 10.25^+0.7^_-3.3_M_Jup_. These measurements represent the first astrometric determination of mutual inclination between objects in an extrasolar planetary system, which we find to be 29.9+/-1{deg}. The combined RV measurements also reveal a long-period trend indicating a fourth planet in the system. We investigate the dynamic stability of this system and analyze regions of stability, which suggest a probable mass of {upsilon} And A b. Finally, our parallaxes confirm that u And B is a stellar companion of {upsilon} And A.
Astrometric positions of the five largest Uranian satellites from 750 CCD frames taken at the oppositions of 1995 through 1998 are presented. The images were obtained over 35 nights. Observed positions are compared with the calculated positions from GUST86. The standard deviations are better than 0.05" for the four largest satellites and 0.08" for Miranda.
In this paper, we publish measurements of 864 positions of the major satellites of Uranus made in 1995-1997 using CCD (1024"*1024") detectors attached to the 1.56-metre Astrometric Telescope at the Sheshan station near Shanghai. Analysis of the data as inter-satellite positions shows that the observations of Ariel, Umbriel, Titania and Mirand relative to Oberon have root-mean-square residuals of 0.03"-0.05", except for the innermost and faintest satellite Miranda, whose residuals exceeded 0.08" due to the proximity of Uranus.
Catalogs of 145 astrometric positions of Uranus and 4 its moons U1-U4 and 62 positions of Neptune and Triton have been compiled with Tycho-2 as a reference frame from photographic observations obtained at the Main Astronomical Observatory, National Academy of Sciences of Ukraine, in 1963-1990. Astronegatives have been digitized with an Epson Expression 10000XL commercial scanner in 16-bit grayscale with a resolution of 1200 dpi. Reduction has been performed in the LINUX-MIDAS-ROMAFOT software supplemented with additional modules for the precise positional determination. The internal positional accuracy of the reduction is 0.04-0.25" for both coordinates and 0.21-0.65m for photographic magnitudes of the Tycho-2 catalog. Gallery of plate images used for catalogs: http://gua.db.ukr-vo.org/catalog_gallery.php?catn=neptun_1963_1990 http://gua.db.ukr-vo.org/catalog_gallery.php?catn=uran_1963_1990
URAT is a follow-up project to the successful UCAC project using the same astrograph but with a much larger focal plane array and a bandpass shifted further to the red. Longer integration times and more sensitive, backside CCDs allowed for a substantial increase in limiting magnitude, resulting in about 4-fold increase in the average number of stars per square degree as compared to UCAC. Additional observations with an objective grating largely extend the dynamic range to include observations of stars as bright as about 3rd magnitude. Multiple sky overlaps per year result in a significant improvement in positional precision as compared to UCAC. A URAT1 release paper for the Astronomical Journal is in preparation. URAT1 is an observational catalog at a mean epoch between 2012.3 and 2014.6; ot covers the magnitude range 3 to 18.5 in R-band, with a positional precision of 5 to 40 mas. It covers most of the northern hemisphere and some areas down to -24.8{deg} in declination.
The URAT Parallax Catalog (UPC) consists of 112177 parallaxes. The catalog utilizes all Northern Hemisphere epoch data from the United States Naval Observatory (USNO) Robotic Astrometric Telescope (URAT). This data includes all individual exposures from April 2012 to June 2015 giving a larger epoch baseline for determining parallaxes over the 2-year span of the First USNO Robotic Astrometric Telescope Catalog (URAT1) (Zacharias et al., 2015, Cat. I/329) published data. The URAT parallax pipeline is custom code that utilizes routines from (Jao, C.-W., 2004, PhD thesis Georgia Stat), the JPL DE405 ephemeris and Green's parallax factor (Green, R.M., 1985, Spherical Astronomy) for determining parallaxes from a weighted least-squares reduction. The relative parallaxes have been corrected to absolute by using the distance color relation described in (Finch et. al, 2014, Cat. J/AJ/148/119) to determine a mean distance of all UCAC4 reference stars (R=8-16 mag) used in the astrometric reductions. Presented here are all significant parallaxes from the URAT Northern Hemisphere epoch data comprising of 2 groups: a) URAT parallax results for stars with prior published parallax, and b) first time trigonometric parallaxes as obtained from URAT data of stars without prior published parallax. Note, more stringent selection criteria have been applied to the second group than the first in order to keep the rate of false detections low. For specific information about the astrometric reductions please see 'The First U.S. Naval Observatory Robotic Astrometric Telescope Catalog' published paper (Zacharias et al., 2015AJ....150..101Z, Cat. I/329). For complete details regarding the parallax pipeline please see 'Parallax Results From URAT Epoch Data' (Finch and Zacharias, 2016, AJ, in press). This catalog gives all positions on the ICRS at Epoch J2014.0; it covers the magnitude range 6.56 to 16.93 in the URAT band-pass, with an average parallax precision of 4.3mas for stars having no known parallax and 10.8mas for stars matched to external parallax sources. This catalog covers the sky from about North of -12.75{deg} declination. This catalog was matched with the Hipparcos catalog, Yale Parallax Catalog, (Finch & Zacharias, 2016, AJ, in press), MEarth (Dittmann et. al., 2014ApJ...784..156D) and the SIMBAD database to obtain known parallax and star names. For stars matched to SIMBAD using the automated search feature, only the parallaxes are given so no information on the parallax errors or source for the parallax are reported for those stars in this catalog. A flag is included to show which catalog or database the URAT parallax was matched with. Only the data from the first catalog that was matched is reported here according to the following priority list. This means for example, if a star was matched with Hipparcos, that information was used while possible other catalog data are not listed here. -------------------------------------------------------- # stars flg catalog -------------------------------------------------------- 53500 0 no catalog match 55549 1 Hipparcos 254 2 Yale Parallax Catalog 1041 3 Finch and Zacharias 2016 (UPM NNNN-NNNN) 1431 4 MEarth parallaxes 402 5 SIMBAD Database (w/parallax) -------------------------------------------------------- 112177 total number stars in catalog -------------------------------------------------------- Not all parallaxes from the URAT epoch data are included in this catalog. Only those data meeting the following criteria have been included. For the epoch data we only used data having a FWHM<=7.0pixel; amplitude between 500 and 30000ADU; sigma x,y <=90.0mas; number of observations >=20 and epoch span>=1.0 years. The limits imposed on individual image amplitude, image profile width (FWHM) and position fit errors (sigma) are set to not allow saturated stars, stars with too few photons or poorly determined positions to be used in the parallax solution. We present all URAT parallax solutions having a known parallax from an external data source regardless of the quality of the solution (srcflg=1-5). This was done for the user to better understand the limitations for determining parallaxes with the current URAT epoch data. For the remaining URAT parallaxes without a match to any published trigonometric parallax (srcflg=0) we only present a parallax solutions having: 1) a parallax error <=10mas 2) a parallax error <=1/4 the relative parallax 3) epoch span >=1.5 years 4) number of observations used >=30 5) fit sigma<=1.4 (unit weight) 6) average image elongation <1.1. All of these cuts have been implemented in an attempt to lower the number of possible erroneous parallax solutions entering our catalog. However, the URAT reduction process does not take provisions for close doubles (blended images) of arcsecond-level separations. Many of the parallaxes, particularly those with large mean elongation, large parallax error, large fit sigma and many rejected observations are possibly blended images leading to a higher chance of an erroneous parallax solutions. A visual inspection of all residual plots and real sky images would not be practical for the entire catalog. However, we have included information in the catalog to help the user to determine if a solution should be investigated further.
