PZT Observations Research Articles

Error analysis of proper motions in decination obtained for 807 Hipparcos stars from PZT observations over many decades

AbstractAfter publication of the Hipparcos catalogue (in 1997), a few new astrometric catalogues have appeared (TYCHO‐2, ARIHIP, etc.), as a good combination of the Hipparcos satellite and ground‐based data, to get more accurate coordinates and proper motions of stars than the Hipparcos catalogue ones. There are also investigations on improving the Hipparcos coordinates and proper motions by using the astrometric observations of latitude and universal time variations (via observed stars referred to Hipparcos catalogue), together with Hipparcos data, carried out during the last few years. These kind of ground‐based data were collected at the end of the last century by J. Vondrák. There are about 4.4 million optical observations made worldwide at 33 observatories and with 47 instruments during 1899.7–1992.0; our Belgrade visual zenith telescope data (for the period 1949.0‐1986.0) were included. First of all, these data were used to determine the Earth Orientation Parameters – EOP, but they are also useful for the opposite task – to check the accuracy of coordinates and proper motions of Hipparcos stars which were observed from the ground over many decades. Here, we use the latitude part of ten Photographic Zenith Tubes – PZT data (more than 0.9 million observations made at 6 observatories during the time interval 1915.8–1992.0), and combine them with the Hipparcos catalogue ones, with suitable weights, in order to check the proper motions in declination for 807 common PZT/Hipparcos stars (and to construct the PZT catalogue of μδ for 807 stars). Our standard errors in proper motions in declination of these stars are less than or equal to the Hipparcos ones for 423 stars. The mean value of standard errors of 313 stars observed over more than 20 years by PZT is 0.40 mas/yr. This is 53% of 0.75 mas/yr (the suitable value from the Hipparcos catalogue). We used the Least Squares Method – LSM with the linear model. Our results are in good agreement with the Earth Orientation Catalogue – EOC‐2 and the new Hipparcos ones. The main steps of the method and the investigations of systematic errors in determined proper motions (the proper motion differences with respect to the Hipparcos values, the EOC‐2 ones and the new Hipparcos ones, as a function of α, δ, and magnitude) are presented here. A comparison of the four catalogues by pairs shows that there is no significant relationship between the differences of their μδ values and magnitudes and color indices of the common 807 stars. All catalogues have relatively small random and systematic errors which are close to each other. However, the comparison shows that our formal errors are too small. They are underestimated by a factor of nearly 1.7 (for EOC‐2, it is 2.0) if we take the new Hipparcos (or Hipparcos) data as reference (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Periodic fluctuations at frequency of the nearly diurnal free wobble in Ondřejov PZT observations

The regular astronomical determinations of the geographic latitude and UT from Ondřejov PZT observations were used to estimate the fluctuations with a frequency of 1.00217 of the sidereal day, corresponding to the theoretical value of the frequency of the nearly diurnal free wobble of the pole. The combined polar wobble and nutation as reflected in astronomical observations was analysed, and a method of estimating the amplitudes of the periodic components, based on observing changes of latitude and time during the separate observation nights, is proposed. The numerical solution indicates that fluctuations which can be considered a manifestation of retrograde free nutation with an amplitude of approximately 0.02″, are present in the PZT observations.

(α−2L) Terms as Obtained from PZT Observations

Periodic terms with arguments such as (α−2L) and (2α−2L) etc. which appear via various phenomena in the results of time and latitude observations by PZT are summarized in analytical forms in order to clarify their mutual relation. Numerical values in time and latitude for these terms to be expected at the Tokyo PZT are also given. From the data of time observations obtained by the Tokyo PZT during the past 15 years, amplitudes of the terms, cos(α−2Lα) and sin(2α−2Lα) in time, are obtained as +0.72 and 1.21 ms, respectively. These results give the value of (l+k-ℓ) as 1.14, and the values of nutation coefficients for 2L, and

Polar Coordinates and UT1 - UTC from PZT Observations

Use of new techniques (Doppler, laser, VLBI) has yielded such results that many astronomers believe that in the near future these techniques will replace classical instruments for observations of the Earth's rotation. None of the modern techniques has furnished observational series which demonstrate that systematic errors in the polar coordinates and UT1 are stable over sufficiently long intervals. Investigations of known phenomena such as sudden changes of the secular term in UT1 - UTC (Munk and MacDonald, 1960), changes of the amplitude and phase of the seasonal irregularities (Fliegel and Hawkins, 1967; Pavlov and Staritzin, 1962), secular motion of the mean pole (Mihailov, 1971; Markowitz, 1960), continental drift (Stoyko, 1938; Djurovic, 1976), quasi-diurnal nutation of Molodenskij (Popov, 1963; Toomre, 1974; Rochester et al., 1974), etc., are complicated by the existence of systematic error variations (accuracy), and to a smaller degree, on the accidental errors (precision). The BIH and IPMS make use of individual series of astronomical latitude. ϕi, and (UTO - UTC)i from up to 82 classical instruments (Guinot, 1976). If the systematic errors in these series are independent, the polar coordinates and UT1 - UTC determined from a combination of observational series would result in an improvement of accuracy by at least one order of magnitude through the mutual compensation of the variation in systematic errors. At present, however, it is uncertain whether mutual independence of modern observations (a basic condition for mutual compensation of errors) will be better than that of the classical instruments.

Polar Motion and Earth Rotation Monitoring in Canada

PZT observations of the Earth's rotation and polar motion have been carried out from observatories near Ottawa and Calgary since 1952 and 1968 respectively. A comprehensive re-evaluation and analysis of the PZT data is currently under way, using a new self-contained computer program which can easily accommodate changes of astronomical constants as well as modifications of the star catalogue.

Environmental Systematics and Astronomical Refraction, I

The first results of a planned continuing investigation of astronomical refraction are reported in this paper. Pure and anomalous refraction are investigated using meteorological data and environmental models. Numerical methods based upon Chebyshev polynomials are developed. Applications are made to Winslow, Arizona (which is somewhat similar to El Leoncito, Argentina), and to results of PZT observations made in Washington, D.C.

Fortnightly terms in PZT observations

view Abstract Citations (5) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fortnightly terms in PZT observations O'Hora, N. P. J. Abstract Analysis of the latitude and time observations of the Herstmonceux PZT support Atkinson's hypothesis that "dynamical variations" in transit observations have their origin in the conventional method of correcting for nutation. Periodogram solutions, over the range 13.5-14.9 days have disclosed three well defined periodic terms. The term with period 14.19 days agrees closely in phase and in duration with that of the alias cycle of the diurnal nutation term computed by Atkinson. Values obtained for the other two fortnightly terms confirm the results of earlier investigations. Publication: The Astronomical Journal Pub Date: December 1973 DOI: 10.1086/111515 Bibcode: 1973AJ.....78.1115O full text sources ADS |

On the Results of the Mizusawa PZT Observations

On the Results of the Mizusawa PZT Observations