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Astron. Astrophys. 355, 398-405 (2000)

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Definition of the Celestial Ephemeris Origin and of UT1 in the International Celestial Reference Frame *

N. Capitaine 1, B. Guinot 1 and D.D. McCarthy 2

1 Observatoire de Paris, DANOF/UMR8630-CNRS, 61, avenue de l'Observatoire 75014 Paris, France (capitain@danof.obspm.fr)
2 U.S. Naval Observatory, 3450 Massachussetts Avenue NW, Washington D.C. 20392-5420, USA (dmc@maia.usno.navy.mil)

Received 12 August 1999 / Accepted 7 December 1999


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). 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.

Key words: astrometry – ephemerides – reference systems – time

* Table 1 is only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/355/398 ( or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/355/398

Send offprint requests to: N. Capitaine

Correspondence to: capitain@danof.obspm.fr

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000