scholarly journals Densifying the Optical Reference Frame: The Tycho-2 Catalog of 2.5 Million Stars

2000 ◽  
Vol 180 ◽  
pp. 75-79
Author(s):  
S.E. Urban ◽  
G.L. Wycoff
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Proper Motions ◽  
Naval Observatory ◽  
Optical Reference ◽  
The Mean ◽  
The U.S

AbstractSince the establishment of the Hipparcos Catalog as the defining source of the optical reference frame, densification beyond its ≈ 120,000 stars has been made possible by the utilization of the Tycho-1 Catalog. The ACT, combining the old Astrographic Catalog (AC) data with the Tycho-1 positions, is the best known example of this. The Tycho-2 consortium, led by E. Høg, has performed new reductions on the Tycho data. This not only has increased the astrometric and photometric accuracies of the original 1 million Tycho-1 stars, but also has added an additional 1.5 million stars. The U.S. Naval Observatory led the effort to compute the proper motions of these 2.5 million stars. They are based not only on the AC data but also include over 140 other ground-based catalogs, all directly reduced to the Hipparcos system. The result of these efforts is the Tycho-2 Catalog, available since February 2000. Positions, proper motions, and BT and VT magnitudes are given for 2.5 million stars. The catalog is 99% complete to V=11.0, and 90% complete to V=11.5. Positional accuracies at the mean epochs vary from < 10 mas for stars V < 9 to just under 100 mas for V > 12. Proper motion accuracies are estimated to be 1.3 mas/year to 3.0 mas/year for the same magnitude ranges. Photometric accuracies range from 0.02 magnitudes for the brightest stars to 0.25 magnitudes for the faintest.

scholarly journals Dense optical reference frames: UCAC and URAT

2007 ◽  
Vol 3 (S248) ◽  
pp. 310-315
Author(s):  
N. Zacharias
Keyword(s):  
Reference Frame ◽  
Focal Plane ◽  
Reference Frames ◽  
Field Of View ◽  
Radio Sources ◽  
Proper Motions ◽  
Naval Observatory ◽  
Optical Reference ◽  
Celestial Reference Frame ◽  
The U.S

AbstractA series of ground-based, dedicated astrometric, observational programs have been performed or are in preparation which provide a dense and accurate optical reference frame. Integral to all these programs are new observations to link the Hipparcos Celestial Reference Frame (HCRF) to the International Celestial Reference Frame (ICRF), based on compact, extragalactic radio sources.The U.S. Naval Observatory CCD Astrograph Catalog (UCAC) 3rd release is in preparation. A pixel re-reduction is in progress to improve astrometric and photometric accuracy as well as completeness of this all-sky reference catalog to 16th magnitude. Optical counterparts of ICRF radio sources have been observed with 0.9-meter telescopes contemporaneously. Scanning of over 5000 early-epoch astrograph plates on StarScan has been completed. These data will improve the proper motions of stars in the 10 to 14 mag range for the UCAC3 release.A 111 million-pixel CCD was successfully fabricated in 2006 and test observations at the USNO astrograph are underway. Four of such detectors will be used for the USNO Robotic Astrometric Telescope (URAT) focal plane assembly. Phase I of URAT will use the astrograph to reach 18th magnitude, while the new 0.85-meter telescope with a 4.5 deg diameter field of view will reach 21st magnitude. The URAT primary mirror has been fabricated.

scholarly journals On the Correction to Precession from Proper Motions Referred to Galaxies

1971 ◽  
Vol 9 ◽  
pp. 163-170 ◽  
Author(s):  
S. Vasilevskis ◽  
A. R. Klemola
Keyword(s):  
Proper Motion ◽  
Direct Relationship ◽  
Fundamental System ◽  
Direct Reference ◽  
Meridian Circle ◽  
Proper Motions ◽  
Obvious Advantage ◽  
Naval Observatory ◽  
Cooperative Project ◽  
The U.S

One of the principal aims of the Lick proper motion program, as conceived and initiated by Wright (1950), was to derive the correction to precession. Ideally, proper motions of stars from a fundamental catalogue should be measured with respect to galaxies. Unfortunately, these stars are too bright for a direct reference to faint galaxies, even with an objective grating and two systems of exposures (2 h and 1 min) on every plate, as employed at Lick. For this reason a cooperative project with the U.S. Naval Observatory was initiated in 1953 (Scott, 1954; Vasilevskis, 1954), with an intention to establish a direct relationship between meridian circle and Lick observations. When Heckmann (1954) proposed the formation of the AGK3, it was agreed to discontinue the cooperation mentioned, so as to make the resources of the U.S. Naval Observatory available for observing the AGK3 reference stars, and then to use the AGK3 as an intermediary for relating the Lick proper motions to a fundamental system. An obvious advantage of this change was offered by the abundance of AGK stars for measurement on Lick plates; a disadvantage is the absence of the AGK3 data south of declination –2.°5.

scholarly journals Extension of The Optical Reference Frame: Ground Based

1998 ◽  
Vol 11 (1) ◽  
pp. 300-303
Author(s):  
N. Zacharias
Keyword(s):  
Reference Frame ◽  
Radio Sources ◽  
Proper Motions ◽  
Magnitude Range ◽  
Optical Reference ◽  
Hipparcos Catalogue ◽  
Optical Wavelengths ◽  
The Mean ◽  
Celestial Reference System ◽  
Celestial Reference Frame

The International Celestial Reference Frame (ICRF) is realized by the positions of 608 compact extragalactic radio sources (Ma & Feissel 1997) with milliarcsecond (mas) and sub-mas accuracy, all being on the same system, the International Celestial Reference System (ICRS). The Hipparcos Catalogue (ESA 1997) is the practical realization of the ICRF at optical wavelengths, giving accurate positions (≈ 1 mas) at the mean epoch of 1991.25 and proper motions (≈ 1 mas/yr) for 117995 stars. This is about 2.5 stars per square degree, most being in the 7 to 9 magnitude range and a few as faint as 12. However, for many astronomical applications the Hipparcos Catalogue is not dense enough and does not reach faint enough magnitudes. The Tycho Catalogue (ESA 1997) provides accurate positions (≈ 25 mas) for about one million stars to magnitude 11, but lacks precise proper motions. Ground-based observations are an efficient way to complement the Hipparcos mission and to extend the optical reference frame to fainter magnitudes and yield a denser grid of astrometric standard stars. New reductions of early epoch photographic data will be used to provide highly accurate proper motions for stars to about magnitude 12. Current and new observational projects will extend the optical reference frame to even fainter magnitudes.

The proper motions of the AGK 3 R and SRS Stars

1978 ◽  
Vol 48 ◽  
pp. 505-514 ◽  
Author(s):  
T. E. Corbin
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Proper Motions ◽  
Naval Observatory ◽  
The Mean ◽  
Work First ◽  
The U.S

The AGK3R and SRS are lists of reference stars containing, respectively, 21,499 stars in the Northern Hemisphere and about 20,500 stars in the Southern Hemisphere. Eleven transit circles contributed to the observations of the AGK3R. The program was a differential one based on theFK4, and the average mean epoch of observation is 1959.0. The compilation of the SRS is still in progress at the U.S. Naval Observatory. As Dr. Hughes has just explained, the SRS positions also will be referred to the system of the FK4, and the mean epochs of observation will be in the latter part of the 1960’s. My task has been to compute the proper motions for these two groups of stars that will permit the use of the observed positions away from the epochs of observation. Since the proper motions of the AGK3R stars have been completed, I will report on that work first.

scholarly journals Linking the FK5 to the ICRF

1998 ◽  
Vol 11 (1) ◽  
pp. 313-316
Author(s):  
F. Mignard ◽  
M. Froeschile
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Harmonic Functions ◽  
Optical Reference ◽  
Precessional Motion ◽  
Precession Constant

Abstract The Hipparcos optical reference frame is compared to the basic FK5 in order to determine the orientation at T0 = 1991.25 and the global spin between the two frames. The components of the spin are significant and suggest a correction the IAU76 value of the precession constant and to a possible non-precessional motion of the equinox of the FK5. The regional errors are analysed with harmonic functions and found to be as large as 150 mas in position and 3 mas/yr in proper motion.

scholarly journals Proper Motions With Respect to the Extragalactic Reference Frame

1990 ◽  
Vol 141 ◽  
pp. 407-417
Author(s):  
A. R. Klemola
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Milky Way ◽  
Proper Motions ◽  
Stellar Proper Motions

The Lick proper motion program, one of several using galaxies as a reference frame, is summarized with a statement of work accomplished for the non-Milky Way sky. The problem of identifying relatively transparent regions at low galactic latitudes is discussed, with tabular results presented for 41 windows from the literature having observable galaxies. These fields may be helpful for attaching stellar proper motions directly to the extragalactic frame.

scholarly journals Correction to Absolute Proper Motion Using the IAS-Galaxy Model

1990 ◽  
Vol 141 ◽  
pp. 427-429
Author(s):  
Kavan U. Ratnatunga
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Theoretical Models ◽  
Galactic Structure ◽  
Coordinate Frame ◽  
Proper Motions ◽  
Software Interface ◽  
The Galaxy ◽  
Galaxy Model ◽  
Star Catalogs

The IAS-Galaxy model (Ratnatunga, Bahcall and Casertano 1989) is a software interface between theoretical models of the Galaxy and observed kinematic distributions. It has been developed for analysis of many kinematic catalogs to study global galactic structure. In addition, the IASG model can be used to estimate corrections needed to derive absolute parallax and absolute proper motion by evaluating, on a star-by-star basis, the expected mean motion of the reference stars.A theoretical Galaxy model is defined on an inertial coordinate frame. Proper motions are measured in a reference frame defined by a fundamental catalog. The observed distribution of proper motions in star catalogs can be directly compared with the expected distributions evaluated using IASG to check the accuracy of the adopted reference frame in realizing the inertial coordinate frame in the sky.

scholarly journals Globular clusters in the era of precision astrometry

2019 ◽  
Vol 14 (S351) ◽  
pp. 412-415
Author(s):  
Paolo Bianchini
Keyword(s):  
Formation Mechanism ◽  
Proper Motion ◽  
Measurement Errors ◽  
Globular Clusters ◽  
Tangential Component ◽  
Proper Motions ◽  
The Mean ◽  
Motion Measurements ◽  
Precision Astrometry

Abstracthe study of the kinematics of globular clusters (GCs) offers the possibility of unveiling their long term evolution and uncovering their yet unknown formation mechanism. Gaia DR2 has strongly revitalized this field and enabled the exploration of the 6D phase-space properties of Milky Way GCs, thanks to precision astrometry. However, to fully leverage on the power of precision astrometry, a thorough investigations of the data is required. In this contribution, we show that the study of the mean radial proper motion profiles of GCs offers an ideal benchmark to assess the presence of systematics in crowded fields. Our work demonstrates that systematics in Gaia DR2 for the closest 14 GCs are below the random measurement errors, reaching a precision of ∼0.015 mas yr−1 for mean proper motion measurements. Finally, through the analysis of the tangential component of proper motions, we report the detection of internal rotation in a sample of ∼50 GCs, and outline the implications of the presence of angular momentum for the formation mechanism of proto-GC. This result gives the first taste of the unparalleled power of Gaia DR2 for GCs science, in preparation for the subsequent data releases.

scholarly journals The Asteroid Mass Determination Project at The U.S. Naval Observatory

1999 ◽  
Vol 172 ◽  
pp. 361-362
Author(s):  
James L. Hilton ◽  
Ronald C. Stone
Keyword(s):  
High Precision ◽  
Mass Determination ◽  
Mean Motion ◽  
Naval Observatory ◽  
Before And After ◽  
Change In The Mean ◽  
The Mean ◽  
The Masses ◽  
The U.S ◽  
Better Than

Asteroid masses are the largest source of unmodeled forces in current planetary ephemerides research. Williams (1984) showed that the asteroids produce km size perturbations in the position of Mars. However, the masses of only three asteroids are known to better than 10%, and only six other asteroid masses have been determined at all.Detecting the mass of an asteroid is difficult because the observed quantity is the change in the mean motion of a second, perturbed asteroid. Asteroid masses are small, so the change in the mean motion is typically on the order of 0."015 yr−1. Thus, excellent orbit determinations are needed both before and after the perturbing encounter. This requires high precision observations over as many oppositions as possible.Hilton (1997) determined the mass of 15 Eunomia to within 25% by detecting perturbations of 1313 Berna. The greatest source of uncertainty in determining the mass of Eunomia was the very poor coverage and accuracy of pre-encounter observations. Hilton (1998) has determined the masses of 1 Ceres, 2 Pallas and 4 Vesta, all based on mutual interactions. The uncertainties in the masses are 1% for Ceres, 3% for Pallas, and 7% for Vesta. The masses of Ceres and Pallas are the best so far, and the mass for Vesta corroborates previous determinations of its mass.

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