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- ID:
- ivo://CDS.VizieR/J/A+A/355/398
- Title:
- Celestial Ephemeris Origin definition
- Short Name:
- J/A+A/355/398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The adoption of the International Celestial Reference System ICRS, and of the corresponding Frame, ICRF, by the 23rd General Assembly of the International Astronomical Union, calls for a redefinition of the departure point on the true equator. Several possibilities have been suggested. This paper considers the use of the non-rotating origin (Guinot, 1979, In: McCarthy D.D., Pilkington J.D. (eds.) Time and the Earth's Rotation. D. Reidel Pub. Co, p. 7). The ``Celestial Ephemeris Origin'' (CEO) is defined here as the non-rotating origin on the equator of the Celestial Ephemeris Pole (CEP). Developments valid at the microarcsecond, based on the best model for precession, nutation and pole offset at J2000.0 with respect to the pole of ICRF, are provided for computing the CEP coordinates and the position of the CEO. It is shown that an operational definition of UT1 based on the CEO leads to values which are insensitive at the microarcsecond level to future improvements of this model.
- ID:
- ivo://CDS.VizieR/J/A+A/400/1145
- Title:
- Celestial Intermediate Pole & Ephemeris Origin
- Short Name:
- J/A+A/400/1145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Expressions for the position of the Celestial Intermediate Pole (CIP) and the Celestial Ephemeris Origin (CEO) in the Geocentric Celestial Reference System (GCRS) have been computed using the IAU 2000A precession-nutation. These expressions are for use in the new transformation between the GCRS and the International Terrestrial Reference System (ITRS) which is recommended by IAU Resolution B1.8. Various comparisons and numerical checks have been performed between the classical and the new transformations based on the IAU 2000A precession-nutation. These comparisons revealed necessary improvements to be applied to the classical form of the transformation in order to achieve the required level of accuracy. Once these improvements are applied, the consistency between the positions of the CIP in the GCRS corresponding to the classical and the new transformations is at a level of a few microarcseconds after one century. This work has demonstrated that the new method, in addition to providing an explicit separation between precession-nutation of the equator from Earth rotation, is more simple, compact and direct than the classical one, achieving accuracies at the level of a few microarcseconds with greatly reduced scope for accidental misuse. The resulting expressions for X, Y and s have been included in the IERS Conventions 2000.
- ID:
- ivo://CDS.VizieR/VI/63
- Title:
- Earth Orbit, Precession and Insolation -20Myr to +10Myr
- Short Name:
- VI/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- La93 is a program for computing the precession and obliquity of the Earth for various values of 1) the tidal effect of the Moon (CMAR) 2) the dynamical ellipticity of the Earth (FGAM) The nominal solution La90 corresponds to (CMAR = 0., FGAM = 1). The general solution will be called La93(CMAR,FGAM), thus La90 = La93(0.,1.) and La93(1.,1.) is obtained with the same tidal effect as in Quinn, Tremaine, Duncan (1991), although these solutions are not completely identical (see Laskar, Joutel, Boudin, 1993) The files and software of this package can be used in three different manners: 1) Contruction and Use of the nominal solution La93(0,1) The ASCII files ORBEL*.ASC contain the nominal orbital solution. The ASCII files PREC0*.ASC contain the nominal precession solution. The ASCII files CLIVAR0*.ASC contain the nominal climatic solution. The files PREC*.ASC and CLIVAR*.ASC can also be generated from the enclosed files (see section 2) For the computation of insolation quantities, the user will execute the 'prepinsol' step, and then 'insola'. 2) Construction of a parametrized La93(CMAR, FGAM) new solution The user reconstructs a complete La93(CMAR, FGAM) solution. The compilation of all required programs is obtained by running the command 'make' on a Unix machine. The preparation step 'prepa' needs to be done once, in order to prepare the necessary binary files. Then 'integ' will construct the new solutions for the given parameters (CMAR, FGAM). Alternatively, change in the Makefile the values of CMAR and FGAM before running the 'make clean' command (removes the files computed using the preceding values of CMAR and FGAM), and 'make La93'. 3) Changes in the model of precession, for example to take into account some feedback resulting from redistribution of the ice on the Earth resulting from climate changes. In this case, and in this case only, the user needs to edit the FORTRAN file integ.f More precisely, the subroutines which can be eventually modified are SUBROUTINE INIPRE(IPT) SUBROUTINE PRECES(t,AK,AH,AQ,AP,DK,DH,DQ,DP,AKI,DKI) The users may also want to adapt the driver INTEG to his specific needs
- ID:
- ivo://CDS.VizieR/J/A+A/531/A6
- Title:
- Evolution of solar irradiance during Holocene
- Short Name:
- J/A+A/531/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Long-term records of solar radiative output are vital for understanding solar variability and past climate change. Measurements of solar irradiance are available for only the last three decades, which calls for reconstructions of this quantity over longer time scales using suitable models. We present a physically consistent reconstruction of the total solar irradiance for the Holocene.
- ID:
- ivo://CDS.VizieR/VIII/107
- Title:
- GLEAM sources ionospheric position shifts
- Short Name:
- VIII/107
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Nearly 200 hours of observing with the Murchison Widefield Array (MWA) radio telescope during the Galactic and Extra-galactic All-sky MWA (GLEAM) survey were used to assemble images of ionospheric structure. These images cover a nearly 50 degree-wide area on the sky at a cadence of 10 minutes over many 5-7 hours-long observing runs. They are generated by tracking the apparent motions of ~200-800 cosmic radio sources caused by changes in the transverse gradient of the ionospheric total electron content. Spectral analysis of these images revealed that the dataset was dominated by three distinct signatures. The first is consistent with field-aligned structures within the topside ionosphere/lower plasmasphere previously imaged with the MWA. The second are structures that are relatively large and aligned nearly east/west. Regional weather data implies that these are preferentially detected when there is a noticeable shear within the sub- tropical jet stream, which passes near the MWA. This suggests that this signature may be related to gravity waves launched by jet stream shear. The final signature is consistent with the properties of so-call electro-buoyancy waves that are known to occur at midlatitudes at night. Detections of these were more common when regional sporadic-E was present, supporting a proposed connection between these waves and polarization electric fields that may arise within sporadic-E. We discuss the implications for future observations with the Square Kilometer Array.
- ID:
- ivo://CDS.VizieR/J/A+A/532/A89
- Title:
- La2010: orbital solution for long term Earth motion
- Short Name:
- J/A+A/532/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here a new solution for the astronomical computation of the orbital motion of the Earth spanning from 0 to -250Myr. The main improvement with respect to our previous numerical solution La2004 is an improved adjustment of the parameters and initial conditions through a fit over 1Myr to a special version of the highly accurate numerical ephemeris INPOP08 (Integration Numerique Planetaire de l'Observatoire de Paris). The precession equations have also been entirely revised and are no longer averaged over the orbital motion of the Earth and Moon. This new orbital solution is now valid over more than 50Myr in the past or into the future with proper phases of the eccentricity variations. Owing to the chaotic behavior, the precision of the solution decreases rapidly beyond this time span, and we discuss the behavior of various solutions beyond 50Myr. For paleoclimate calibrations, we provide several different solutions that are all compatible with the most precise planetary ephemeris. We have thus reached the time where geological data are now required to discriminate between planetary orbital solutions beyond 50Myr.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A102
- Title:
- Mesospheric sodium properties
- Short Name:
- J/A+A/565/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The performance of laser guide star adaptive optics (AO) systems for large optical and infrared telescopes is acted by variability of the sodium layer, located at altitudes between 80 and 120km in the upper mesosphere and lower thermosphere. The abundance and density structure of the atomic sodium found in this region is subject to local and global weather ects, planetary and gravity waves and magnetic storms, and is variable on time scales down to tens of milliseconds, a range relevant to AO. It is therefore important to characterize the structure and dynamical evolution of the sodium region on small, as well as large spatial and temporal scales. Parameters of particular importance for AO are the mean sodium altitude, sodium layer width and the temporal power spectrum of the centroid altitude. We have conducted a three-year campaign employing a high-resolution lidar system installed on the 6-m Large Zenith Telescope (LZT) located near Vancouver, Canada. During this period, 112 nights of useful data were obtained.
- ID:
- ivo://CDS.VizieR/J/A+A/450/855
- Title:
- Methods for CIP and CIO localisation
- Short Name:
- J/A+A/450/855
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The precession-nutation transformation describes the changing directions on the celestial sphere of the Earth's pole and an adopted origin of right ascension. The coordinate system for the celestial sphere is the geocentric celestial reference system, and the two directions are the celestial intermediate pole (CIP) and the celestial intermediate origin (CIO), the latter having supplanted the equinox for this purpose following IAU resolutions in 2000. The celestial coordinate triad based on the CIP and CIO is called the celestial intermediate reference system; the prediction of topocentric directions additionally requires the Earth rotation angle (ERA), the counterpart of Greenwich sidereal time (GST) in the former equinox based system. The purpose of this paper is to review the different ways of calculating the CIP and CIO directions to precisions of a few microarcseconds over a time span of several centuries, meeting the requirements of high-accuracy applications.
- ID:
- ivo://CDS.VizieR/J/A+AS/116/473
- Title:
- Nutation modeling and VLBI observations
- Short Name:
- J/A+AS/116/473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using geodetic and astrometric VLBI acquired between 1984-1994, we have determined coefficients in the nutation series with uncertainties of 10microarcseconds. This level of accuracy is quite sufficient to differentiate between alternate theories of nutation. We show that small terms predicted using the Kinoshita & Souchay (1990) rigid Earth theory of nutation revised by Souchay & Kinoshita (1996), agree well with the VLBI results at periods where the non rigid Earth corrections are reliable. These terms are different or absent from the Kinoshita (1977) theory that is the basis for the standard IAU 1980 model. We propose a nutation series based on the Kinoshita & Souchay theory using the Wahr (1979) transformation for a non rigid Earth that can be useful where the physical interpretation of the smaller terms is important. This series, called VKSNRE95.1, includes corrections to the nine largest terms derived from VLBI observations.
