Australia Telescope National Facility

Responsibility for the definition of time scales left the astronomical community some 40 years ago when, in 1967, the second became defined by an atomic transition in the International System of units SI and when TAI was defined as the primary international time scale in 1971. Atomic time is now 107 times more stable than the Earth rotation and some 104 times more stable than the planetary orbital motions that were used to define time until 1967.

But time still interacts with astronomy in many ways: as the independent variable for the description of all dynamical systems, its stability allows one to study these systems and their perturbations. Time is therefore of major importance for astronomers, with time scales based on the SI second for practical applications and coordinate time scales for theoretical developments. Precise timing of the rotational and orbital periods of pulsars has the potential to contribute to the long-term stability of International Atomic Time (TAI), thereby returning some aspects of time keeping to astronomy. Furthermore, since observational techniques rely on the measurement of the time of propagation of electromagnetic signals, astronomy provides an important testing ground for relativity.

Although universal time is not used any more to provide the official time, it still reflects the Earth rotation and dictates the leap seconds and hence UTC, the international reference for time and frequency. The future of leap seconds is presently still a subject of debate led by the ITU-R Special Rapporteur Group. In parallel, the knowledge of UT1 is needed for any coordinate transformation between terrestrial and celestial reference systems. Together with the atomic time, UT1 serves precise orbit determination for both space research and Earth studies. The recent measurements of multiple space geodetic techniques, individually or in combination, provide high precision monitoring of LOD and UT1, and allow predictions as needed for real time applications. This improved accuracy on the UT1/LOD measurements also brings a new set of constraints for geophysical models.

The present realizations of the Terrestrial Time TT are the International Atomic Time TAI provided by the BIPM on a monthly basis, and TT(BIPM) based on the reprocessing using all primary frequency standard measurements. TT(BIPM) is presently the best reference to estimate the long-term stability of any other time scale, and in particular the long-term stability of pulsars. Thanks to the recent development of new frequency standards, and to the parallel progress in time scale algorithms and in time transfer techniques, the present atomic time scale stabilities and accuracies has been significantly improved.

Pulsars are incredibly stable clocks with a stability that rivals the best atomic clocks. Many pulsars are members of a binary system, enabling very precise measurement of the gravitational interactions between massive bodies and tests of gravitational theories. Such measurements have already given the most precise verification of Einstein's general relativity in the strong-field case. Future observations will reveal higher-order gravitational perturbations, providing even more stringent tests of gravitational theories. Recent developments of "pulsar timing arrays", in which a large sample of millisecond pulsars are regularly timed, have the potential to establish a time scale which is more stable than the best atomic timescales over long time intervals and hence to investigate the stability of these time scales.

They also are sensitive to errors or omissions in the planetary ephemeredes used to model the Earth's motion and hence to improve those ephemeredes. Finally, they have the potential to make a direct detection of gravitational waves from astronomical sources. Such measurements would open up a new window on the Universe and provide important constraints on models for the early Universe and galaxy evolution.

• UT1/LOD realization and accuracy
• Geophysical impact on UT1
• Short- and long-term variations of UT1
• Use of UT1 for astro-geodetic studies
• UT1 prediction

• Stability of TAI, TT(BIPM)
• Impact of new frequency standards on SI time scales
• GNSS time scales
• Time transfer
• Recent Developments with Leap Seconds

• Techniques of precision pulsar timing
• Pulsar time scales
• Pulsar tests of gravitational theories
• Pulsar Timing Arrays and detection of gravitational waves
• Improving solar-system ephemeredes
• Pulsar Timing Noise

The abstracts must be submitted before March 1st, 2009, via the website of the IAU General Assembly: http://www.astronomy2009.com.br/
sub-menu “Instructions for Presenters”

	9:00- 9:30		Invited		D. Gambis, C. Bizouard		Monitoring UT1 from astro-geodetic techniques. State of the art and prospective.
	9:30- 9:45				V. Zharov		Instability of the celestial reference frame and effect on UT1
	9:45-10:00				S. Klioner		On the Relativistic Theory of Earth Rotation
	10:00-10:15				J. Vondrak , C. Ron , V. Stefka		New solution of Earth Orientation Parameters in 20th century
	10:15-10:30				N. Capitaine , P. Wallace		Implementation of the IAU 2000 definition of UT1 in astronomy

	11:00-11:30		Invited		R. Gross		Impact of Geophysical Fluids on UT1 Variations
	11:30-11:45				S. Englich , H. Schuh , R. Weber		Short-term tidal variations in UT1: compliance between modelling and observation
	11:45-12:00				H. Schuh , J. Boehm , S. Englich , A. Nothnagel		Determination of UT1 by VLBI
	12:00-12:15				A. Brzezinski, N. Capitaine		Semidiurnal signals in UT1/LOD due to the influence of tidal gravitation on the triaxial structure of the Earth
	12:15-12:30				W. Wooden , B. Luzum , N. Stamatakos		Current Status and Future Directions for IERS RS/PC Predictions of UT1

	14:00-14:15				T. Fukushima		Time Ephemeris
	14:15-14:25				D. D. McCarthy		The Future of the Leap Second
	14:25-15:30						POSTER SESSION

	16:00-16:25		Invited		G. Petit		Atomic time scales TAI and TT(BIPM): present performances and prospects
	16:25-16:45		Invited		D. Matsakis		Algorithms for UTC and TT
	16:45-17:00				P. Uhrich , P. Tuckey		The use of Galileo signals for time transfer metrology
	17:00-17:15				E.F. Arias , G. Panfilo		Impact of new frequency standards on the international time scales
	17:15-17:30				H. Takiguchi , Y. Koyama , R. Ichikawa , T. Gotoh , A. Ishii , T. Hobiger , M. Hosokawa		VLBI Measurements for Frequency Transfer

	9:00- 9:30		Invited		S. Kopeikin		Stability of pulsar rotational and orbital periods
	9:30- 9:45				J.O. Urama , A.E. Chukwude		Large glitches, small glitches and timing noise
	9:45-10:00				N. Wang		Pulsar glitches detected at Urumqi Observatory
	10:00-10:15				A. Rodin		Pulsar timing array
	10:15-10:30				M. Pshirkov		Investigating ultra-long gravitational waves with measurements of pulsars rotational parameters

	11:00-11:30		Invited		M. Kramer		Binary pulsar tests of gravitational theories
	11:30-11:45				Y. Ilyasov , V. Zharov , M. Sekido		Impact of Pulsar Giant Pulses on Distant Clocks Comparison
	11:45-12:00				R. Manchester		Detecting Gravitational Waves with Pulsar Timing
	12:00-12:15				V. Potapov , S. Kopeikin		Timing of binary pulsars and the search for the low-frequency gravitational waves.

The instructions for presenters can be found on the IAU website : http://www.astronomy2009.com.br/instrpres.html

The proceedings will be published in
HIGHLIGHTS OF ASTRONOMY, Volume 15
Editor-in-Chief: Ian F Corbett
Publisher: Cambridge University Press (CUP, UK)

The proceedings must be written in Latex. You can find the author's style file as well as a number of sample and ‘readme’ files to create your paper, on the IAU website, at the following address: http://www.iau.org/static/scientific_meetings/authors_proceedings/

Your contribution should be send to p.defraigne@oma.be by email no later than the September 15, 2009, so that we can assemble all the papers and send the complete volume to the IAU in the deadline. As we receive only a maximum of 30 pages, only summaries can be proposed. These should be of 2 pages for invited talks and 1 page for oral contributions. There is unfortunately no possibility to include a paper for the poster presentations. All Authors are also requested to download the IAU Copyright Form from the IAU website, to complete it and to send it to Pascale Defraigne (see the contact info above), as the Editor of the JD. She will then send the complete set of IAU Copyright Forms, together with the complete manuscript of the JD Proceedings, to the IAU.