scholarly journals Corrections of proper motions in declination by using ILS data

2006 ◽  
pp. 95-99 ◽  
Author(s):  
G. Damljanovic ◽  
N. Pejovic
Keyword(s):  
Earth Rotation ◽  
Sufficient Accuracy ◽  
Proper Motions ◽  
Satellite Mission ◽  
Earth Orientation ◽  
The Earth ◽  
Hipparcos Catalogue ◽  
Order Of Magnitude ◽  
Astronomical Satellite ◽  
Good Agreement

There are nowadays numerous astrometric ground{based observations of some stars referred to Hipparcos Catalogue, made at many observatories during the last century. We used the data on latitude variations, covering the period 1899.7 - 1979.0, of visual Zenith Telescopes (ZT) of International Latitude Service (ILS), to improve the Hipparcos proper motions in declination for stars observed at seven ILS stations: Carloforte, Cincinnati, Gaithersburg Kitab, Mizusawa, Tschardjui and Ukiah. About 15 years elapsed since the HIPPARCOS ESA mission (ESA 1997) observations (1991.25 is the epoch of this catalogue), and with the errors of the Hipparcos proper motions close to 1 mas/yr, the error of apparent places of stars is now more than 15 mas; so that it exceeds the error of the Hipparcos positions by one order of magnitude (which is about 1 mas). Also, for some Hipparcos stars, the errors of proper motions are much larger than the averaged value itself, even not realistic at all (Vondr?k et al. 1998); the Hipparcos astronomical satellite mission lasted less than four years, not enough to get a sufficient accuracy of the proper motions. To improve the accuracy of the proper motions for some Hipparcos stars, the ground-based data were used and some new catalogues were published (such as ARIHIP, EOC-2, etc) during the last decade. Our investigations are in accordance with the Earth Orientation Catalogue - EOC (Vondr?k and Ron 2003) one, based on the Earth rotation programmes ground{based data, but we used different method here. Our results yield better proper motions in declination for stars common to ILS and HIPPARCOS and a good agreement with those from EOC-2.

scholarly journals Improvement of Hipparcos proper motions in declination

2006 ◽  
pp. 41-51 ◽  
Author(s):  
Goran Damljanovic ◽  
N. Pejovic ◽  
B. Jovanovic
Keyword(s):  
Optical Observations ◽  
Proper Motions ◽  
Satellite Mission ◽  
Hipparcos Catalogue ◽  
Astronomical Satellite ◽  
Good Agreement

More than a decade elapsed after the HIPPARCOS ESA mission (ESA 1997) observations have been collected. This first astronomical satellite mission was less than 4 years long so that 1991.25 is the epoch of the HIPPARCOS Catalogue. Many other projects have checked or improved HIPPARCOS data. Also, a long series of ground - based optical observations of some stars included in HIPPARCOS Catalogue, made with Photographic Zenith Tubes (PZT) are useful for the task of improving the proper motions of these stars. The ARIHIP Catalogue (after ACT, TYCHO - 2, FK6, GC+HIP, TYC2+HIP) is a combination of the HIPPARCOS and some ground - based data, and the ARIHIP proper motions are more accurate than the HIPPARCOS ones. Here we present a new step of our procedure of calculation; between PZT data we added the HIPPARCOS position with suitable weight - the point with the coordinates (1991:25, 0 . 00 0) in our case. The method was applied to 202 stars observed at Richmond PZTs in the course of a few decades. The result is better proper motions in declination for these HIPPARCOS stars, and a good agreement with ARIHIP proper motions (we found 128 common Richmond and ARIHIP stars to check our result). Also, we present the result for other 74 Richmond stars which are not found in ARIHIP.

scholarly journals Corrected μβ for stars of Hipparcos catalogue from independent latitude observations over many decades

2011 ◽  
pp. 35-41 ◽  
Author(s):  
G. Damljanovic ◽  
I.S. Milic
Keyword(s):  
International Organizations ◽  
Sufficient Accuracy ◽  
Proper Motions ◽  
Earth Orientation Parameters ◽  
Method Of Calculation ◽  
The Earth ◽  
Hipparcos Catalogue ◽  
International Polar ◽  
The Common ◽  
Orientation Parameters

During the last century, there were many so-called independent latitude (IL) stations with the observations which were included into data of a few international organizations (like Bureau International de l'Heure - BIH, International Polar Motion Service - IPMS) and the Earth rotation programmes for determining the Earth Orientation Parameters - EOP. Because of this, nowadays, there are numerous astrometric ground-based observations (made over many decades) of some stars included in the Hipparcos Catalogue (ESA 1997). We used these latitude data for the inverse investigations - to improve the proper motions in declination ?? of the mentioned Hipparcos stars. We determined the corrections ??? and investigated agreement of our ?? and those from the catalogues Hipparcos and new Hipparcos (van Leeuwen 2007). To do this we used the latitude variations of 7 stations (Belgrade, Blagoveschtschensk, Irkutsk, Poltava, Pulkovo, Warsaw and Mizusawa), covering different intervals in the period 1904.7 - 1992.0, obtained with 6 visual and 1 floating zenith telescopes (Mizusawa). On the other hand, with regard that about two decades have elapsed since the Hipparcos ESA mission observations (the epoch of Hipparcos catalogue is 1991.25), the error of apparent places of Hipparcos stars has increased by nearly 20 mas because of proper motion errors. Also, the mission lasted less than four years which was not enough for a sufficient accuracy of proper motions of some stars (such as double or multiple ones). Our method of calculation, and the calculated ?? for the common IL/Hipparcos stars are presented here. We constructed an IL catalogue of 1200 stars: there are 707 stars in the first part (with at least 20 years of IL observations) and 493 stars in the second one (less than 20 years). In the case of ?? of IL stars observed at some stations (Blagoveschtschensk, Irkutsk, Mizusawa, Poltava and Pulkovo) we find the formal errors less than the corresponding Hipparcos ones and for some of them (stations Blagoveschtschensk and Irkutsk) even less than the new Hipparcos ones.

scholarly journals The Observations of the Earth Rotation and the Stellar System

1986 ◽  
Vol 109 ◽  
pp. 133-141
Author(s):  
Koichi Sato ◽  
Koichi Yokoyama ◽  
Kiyotaka Tanikawa ◽  
Yukio Goto
Keyword(s):  
Coordinate System ◽  
Earth Rotation ◽  
Stellar System ◽  
Proper Motions ◽  
Earth Orientation Parameters ◽  
Reference Coordinate System ◽  
Earth Orientation ◽  
The Earth ◽  
Orientation Parameters ◽  
Fundamental Reference

The fundamental reference of the Earth rotation observation by the method of optical astrometry, such as VZT, PZT, astrolabe, transit instrument and so on, relies upon the stellar system. Hence the stellar positions and proper motions, and the celestial reference coordinate system are essential to preserve the system of the Earth orientation parameters determined by the optical astrometry.

scholarly journals Earth Orientation Parameters 1899.7-1992.0 In The Hipparcos Reference Frame

1998 ◽  
Vol 11 (1) ◽  
pp. 553-553
Author(s):  
J. Vondrák ◽  
C. Ron ◽  
I. Pešek ◽  
A. Čepek
Keyword(s):  
Polar Motion ◽  
Universal Time ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
The Earth ◽  
Hipparcos Catalogue ◽  
Time Variations ◽  
Celestial Reference System ◽  
Orientation Parameters ◽  
Made In

The optical astrometry observations of latitude/universal time variations made with 48 instruments at 31 observatories are used to determine the Earth orientation parameters (EOP) since the beginning of the century. The Hipparcos Catalogue is used to bring more than four million individual observations, made in the interval 1899.7-1992.0, into the International Celestial Reference System. The Earth orientation parameters (polar motion, celestial pole offsets and, since 1956.0, also universal time UT1) are determined at 5-day intervals, with average uncertainties ranging from 8 mas (in the eighties) to about 40 mas (in the forties). Making use of very long series of ground-based observations, the solution also leads to the improvement of proper motions of about ten per cent of the observed Hipparcos stars, with precision of ±0.2 — 0.5 mas/yr. In addition, 474 auxiliary parameters, describing the rheological properties of the Earth and seasonal deviations of the observations at contributing observatories, are found. The new solution provides the EOP series suitable for further analyses, e.g., for studying long-periodic polar motion, length-of-day changes or precession/nutation.

scholarly journals Corrections to the Hipparcos proper motions in declination for 807 stars

2008 ◽  
pp. 109-113 ◽  
Author(s):  
G. Damljanovic ◽  
N. Pejovic
Keyword(s):  
Accurate Determination ◽  
Annual Number ◽  
Time Interval ◽  
Proper Motions ◽  
Hipparcos Catalogue ◽  
Time Variations ◽  
Better Than ◽  
Good Agreement

We used the data on latitude variations obtained from observations with 10 classical photographic zenith tubes (PZT) in order to improve the Hipparcos proper motions in declinations ?? for 807 stars. Part of observing programmes, carried out during the last century for the purpose of studying the Earth's rotation, were realized by using PZT instruments. These observations were performed within in the intervals (tens of years) much longer than that of the Hipparcos mission (less than 4 years). In addition, the annual number of observations for every PZT programme star is several hundreds on the average. Though the accuracy of the star coordinates in the Hipparcos Catalogue is by two orders of magnitude better than that of the star coordinates from the PZT observations, the large number of observations performed a much longer time interval makes it possible to correct the Hipparcos proper motions and to improve their accuracy with respect to the accuracy given in the Hipparcos Catalogue. Long term examinations of latitude and time variations were used to form the Earth Orientation Catalogue (EOC-2), aimed at a more accurate determination of positions and proper motions for the stars included. Our method of calculating the corrections of the proper motions in declination from the latitude variations is different from the method used in obtaining the EOC-2 Catalogue. Comparing the results we have established a good agreement between our ?? and the EOC-2 ones for the star sample used in the present paper.

scholarly journals Astrometric star catalogues as combination of Hipparcos/Tycho catalogues with ground-based observations

2004 ◽  
pp. 1-8 ◽  
Author(s):  
J. Vondrák
Keyword(s):  
Universal Time ◽  
Optical Observations ◽  
Proper Motions ◽  
Earth Orientation ◽  
Optical Wavelength ◽  
Primary Representation ◽  
Hipparcos Catalogue ◽  
Time Variations ◽  
Celestial Reference System ◽  
Better Than

The successful ESA mission Hipparcos provided very precise parallaxes positions and proper motions of many stars in optical wavelength. Therefore it is a primary representation of International Celestial Reference System in this wavelength. However, the shortness of the mission (less than four years) causes some problems with proper motions of the stars that are double or multiple. Therefore, a combination of the positions measured by Hipparcos satellite with ground-based observations with much longer history provides a better reference frame that is more stable in time. Several examples of such combinations are presented (ACT, TYCHO-2, FK6, GC+HIP, TYC2+HIP, ARIHIP) and briefly described. The stress is put on the most recent Earth Orientation Catalogue (EOC) that uses about 4.4 million optical observations of latitude/universal time variations (made during the twentieth century at 33 observatories in Earth orientation programmes), in combination with some of the above mentioned combined catalogues. The second version of the new catalogue EOC-2 contains 4418 objects, and the precision of their proper motions is far better than that of Hipparcos Catalogue.

scholarly journals The CEP and Geophysical Interpretation of Modern Earth Rotation Observations

2000 ◽  
Vol 178 ◽  
pp. 585-594 ◽  
Author(s):  
Aleksander Brzeziński
Keyword(s):  
Earth Rotation ◽  
Earth Orientation Parameters ◽  
Earth Orientation ◽  
Conceptual Definition ◽  
The Earth ◽  
Geophysical Interpretation ◽  
Definition Of ◽  
Geophysical Fluids ◽  
Orientation Parameters ◽  
Excitation Parameters

AbstractThe definition of the Celestial Ephemeris Pole (CEP) which is the pole of reference for precession and nutation, should be revised taking into account recent advances in observation and theory. This paper reviews the current realization of the CEP and discusses possible extensions of both the conceptual definition and the realization of the CEP. Attention is focused on the corresponding connections between the Earth orientation parameters describing rotational variations and the related excitation parameters expressing dynamics of the geophysical fluids.

scholarly journals Combination of VLBI Intensive Sessions with GNSS for generating Low latency Earth Rotation Parameters

2019 ◽  
Vol 50 ◽  
pp. 49-56
Author(s):  
Hendrik Hellmers ◽  
Daniela Thaller ◽  
Mathis Bloßfeld ◽  
Alexander Kehm ◽  
Anastasiia Girdiuk
Keyword(s):  
Time Series ◽  
Earth Rotation ◽  
Normal Equation ◽  
Laser Ranging ◽  
Low Latency ◽  
Lunar Laser Ranging ◽  
Earth Orientation ◽  
The Earth ◽  
Earth Rotation Parameters ◽  
Rotation Parameters

Abstract. The Earth Orientation Parameters (EOPs) are published by the Earth Orientation Centre of the International Earth Rotation and Reference Systems Service (IERS). They are provided as the low-latency Bulletin A and the 30 d latency long-term EOP time series IERS 14 C04. The EOPs are a combined product derived from different geodetic space techniques, namely Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) and Very Long Baseline Interferometry (VLBI). Since not all techniques are equally sensitive to every EOP, several parameters rely on specific observation techniques. As an example, dUT1 can only be estimated from VLBI observations. This means VLBI is an essential part of the estimation procedure for consistent EOPs. Within this paper, we are performing a combination of two low-latency space geodetic techniques as they enable the estimation of the full set of Earth Rotation Parameters (ERPs; polar motion, dUT1 and the corresponding rates). In particular, we focus on the development of a robust combination scheme of 1 h VLBI Intensive sessions with so-called GNSS Rapid solutions on the normal equation level of the Gauß-Markov model. The aim of the study is to provide highly accurate low-latency ERPs. So far, a latency of approximately only 1–3 d cold be reached since the main limiting factor is still the latency of the input data. The mathematical background of the applied algorithm is discussed in detail and evaluated by numerical results of empirical investigations. The combination yields a numerical stabilization of the equation system as well as an improvement (reduction) of the corresponding root mean square deviation of the epoch-wise estimated parameters w.r.t. the IERS 14 C04 reference time series.

scholarly journals Tycho Astrometry from 30 Months of Satellite Mission

1995 ◽  
Vol 166 ◽  
pp. 61-68
Author(s):  
E. Høg
Keyword(s):  
Data Processing ◽  
Systematic Errors ◽  
Proper Motions ◽  
Satellite Mission ◽  
Satisfactory Accuracy ◽  
Transit Times ◽  
Hipparcos Catalogue ◽  
Spectral Channels ◽  
Astrometric Data

The Hipparcos satellite's star mapper gives photon counts in two spectral channels simultaneously, close to Johnson B and V. The transit times and the signal amplitudes for each star across two groups of four slits are derived and used for astrometry and photometry, respectively, and this constitutes the Tycho project. The present paper describes results of Tycho astrometric data processing, leading from the transit times to the astrometric parameters of the Tycho stars.Some 30 months of Tycho observations, i.e. about 80 percent of the Hipparcos-Tycho mission, have been used to produce a working catalogue of Tycho positions, proper motions and parallaxes of a million stars. The external errors of this preliminary catalogue have been determined by comparison of 98 000 stars common with a preliminary, but much more accurate Hipparcos catalogue. External systematic errors of positions and annual proper motions are less than 0.5 milliarcsecond (mas) and the accidental errors per star are about 30 mas rms at V = 10.5 mag, the median magnitude of the catalogue. It is concluded that a satisfactory accuracy has been achieved.

scholarly journals Accurate radiometry from space: an essential tool for climate studies

2011 ◽  
Vol 369 (1953) ◽  
pp. 4028-4063 ◽  
Author(s):  
Nigel Fox ◽  
Andrea Kaiser-Weiss ◽  
Werner Schmutz ◽  
Kurtis Thome ◽  
Dave Young ◽  
...  
Keyword(s):  
Climate Models ◽  
Causal Attribution ◽  
International System ◽  
Primary Standard ◽  
Sufficient Accuracy ◽  
Time Base ◽  
Satellite Mission ◽  
The Earth ◽  
System Of Units ◽  
Si Traceability

The Earth's climate is undoubtedly changing; however, the time scale, consequences and causal attribution remain the subject of significant debate and uncertainty. Detection of subtle indicators from a background of natural variability requires measurements over a time base of decades. This places severe demands on the instrumentation used, requiring measurements of sufficient accuracy and sensitivity that can allow reliable judgements to be made decades apart. The International System of Units (SI) and the network of National Metrology Institutes were developed to address such requirements. However, ensuring and maintaining SI traceability of sufficient accuracy in instruments orbiting the Earth presents a significant new challenge to the metrology community. This paper highlights some key measurands and applications driving the uncertainty demand of the climate community in the solar reflective domain, e.g. solar irradiances and reflectances/radiances of the Earth. It discusses how meeting these uncertainties facilitate significant improvement in the forecasting abilities of climate models. After discussing the current state of the art, it describes a new satellite mission, called TRUTHS, which enables, for the first time, high-accuracy SI traceability to be established in orbit. The direct use of a ‘primary standard’ and replication of the terrestrial traceability chain extends the SI into space, in effect realizing a ‘metrology laboratory in space’.

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