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Commission 4 was among the first set of commissions formed within the IAU at its founding in 1919. (Commissions were originally called “Standing Committees.”) During its 96 years of service to the IAU and astronomical community in general, the commission has been fortunate to have been led by many distinguished scientists — see the list of presidents below.
The triennial meeting of Commission 4 was attended by 16 people. All of the presentations from the meeting are provided on the commission website at http://www.iaucom4.org/c4docs.html, so this report provides only summaries.
The Commission 4 Organizing Committee began its work for the 2009-2012 triennium by revising the commission's terms of reference, which serve as our “mission statement.” The new terms of reference are:
(a) Maintain cooperation and collaboration between the national offices providing ephemerides, prediction of phenomena, astronomical reference data, and navigational almanacs.
(b) Encourage agreement on the bases (reference systems, time scales, models, and constants) of astronomical ephemerides and reference data in the various countries. Promote improvements to the usability and accuracy of astronomical ephemerides, and provide information comparing computational methods, models, and results to ensure the accuracy of data provided.
(c) Maintain databases, available on the Internet to the national ephemeris offices and qualified researchers, containing observations of all types on which the ephemerides are based. Promote the continued importance of observations needed to improve the ephemerides, and encourage prompt availability of these observations, especially those from space missions, to the science community.
(d) Encourage the development of software and web sites that provide astronomical ephemerides, prediction of phenomena, and astronomical reference data to the scientific community and public.
Promote the development of explanatory material that fosters better understanding of the use and bases of ephemerides and related data.
Dr. George Kaplan, the current Vice-President of the Commission was nominated to be the new President. Dr. Catherine Hohenkerk was elected to be the next Vice-President of the Commission. As for the Membership of the Organizing Committee, Dr. Vondrak stepped down and Drs William Folkner of JPL and Steve Bell of HMNAO have been added. In the below, we present summaries of the reports from various institutions presented at the business session.
A continuation of this WG was voted for at the IAU GA 2006 in Prague. The International Celestial Reference Frame (ICRF) is defined by the positions of 212 distant quasars at radio wavelengths. The primary, optical reference frame is the Hipparcos Celestial Reference Frame (HCRF), which is the Hipparcos Catalog without astrometric ‘problem’ stars (in: H. Rickman (ed.) 2001, Proceedings IAU XXIV General Assembly, Transactions IAU XXIVB (San Francisco: ASP), Resolution B1.2). The Tycho-2 catalog with its 2.5 million brightest stars forms the first step in the densification of the optical reference frame. However, the limiting magnitude of about V = 12 of the Tycho-2 catalog is not sufficient for most applications in astronomy and the goal of this IAU Working Group is to further extend the grid of highly accurate positions and motions toward more and fainter stars. The web site of this WG is at <ad.usno.navy.mil/dens_wg/>.
JPL planetary ephemeris development has been very active assimilating measurements from current planetary missions and supporting future missions. The NASA Mars Science Laboratory (MSL) mission with launch in 2009 requires knowledge of the Earth and Mars ephemerides with 30m accuracy. By comparison, the accuracy of the Mars ephemeris in the widely used DE405 ephemeris was about 3 km. Meeting the MSL needs requires an ongoing program of range and very-long baseline interferometry measurements of Mars orbiting spacecraft. The JPL ephemeris DE421 was released three months before the landing of the Phoenix mission on Mars, and has met the 300m requirement. Continued measurements are planned to support the MSL landing.
At the 2003 Sydney IAU meeting, Marion Schmitz (Caltech, USA) took over the chair of the Commission 5 Working Group Designations, succeeding Helene Dickel. The Working Group Designations of IAU Commission 5 clarifies existing astronomical nomenclature and helps astronomers avoid potential problems when designating their sources. The most important function of WG Designations during the period 2003-2005 was overseeing the IAU REGISTRY FOR ACRONYMS (for newly discovered astronomical sources of radiation: see the website <http://cdsweb.u-strasbg.fr/cgi-bin/DicForm>) which is sponsored by the WG and operated by the Centre de Données de Strasbourg (CDS). The Clearing House, a subgroup of the WG, screens the submissions for accuracy and conformity to the IAU Recommendations for Nomenclature (<http://cdsweb.u-strasbg.fr/iau-spec.html>). From its beginning in 1997 through August 2006, there have been 132 submissions and 111 acceptances. Attempts to register asterisms, common star names, and suspected variable stars were rejected. The past three years saw 61 acronyms submitted with 50 of them being accepted. (GIRL - yes; WOMEN - no).
This business meeting was held from 16:00 to 17:30. Toshio Fukushima and George Kaplan were welcomed as the next president and vice-president, respectively. The following, in no particular order, are the summary reports from the various offices. The full versions will be made available on the Commission 4 website at <http://iau-comm4.jpl.nasa.gov/>.
The Full-sky Astrometric Mapping Explorer (FAME) is designed to perform an all-sky, astrometric survey with unprecedented accuracy. It will create a rigid astrometric catalog of 4 × 107 stars with 5 < mV < 15. For bright stars, 5 < mV < 9, FAME will determine positions and parallaxes accurate to < 50 μas, with proper motion errors < 50 μas/yr. For fainter stars, 9 < mV < 15, FAME will determine positions and parallaxes accurate to < 500 μas, with proper motion errors < 500 μas/yr. It will also collect photometric data on these 4 × 107 stars in four Sloan Digital Sky Survey colors. NASA selected FAME to be one of five MIDEX missions funded for a concept study. In October 1999, NASA selected FAME for launch in 2004 as the MIDEX-4 mission in its Explorer program.
The Astrographic Catalogue (AC) measures are being reduced at the U.S. Naval Observatory to provide early epoch positions for approximately 5 million stars. The data, when combined with recent observations, provide a baseline of about 100 years with which to compute proper motions. Due to the inhomogeneity of telescopes and measuring techniques used in the AC program, each of the 22 zones is being reduced independently with the Astrographic Catalog Reference Stars (ACRS). The data are analyzed and corrected for radial distortions, tilt, magnitude-dependent terms, coma, and distortions based on reseaux and measuring apparatus. To date, eleven zones have been reduced and are available on the WWW (http://aries.usno.navy.mil/ad/ac.html) or the international data centers. Mean errors of the positional data vary from zone to zone, but are generally in the 190-320 mas range per each image.
The newly reduced AC data are being combined with the USNO’s Twin Astrograph Catalog (TAC) in support of the Sloan Digital Sky Survey. This catalog should be available by the end of 1996. When the Tycho data are released, the AC positions will be used to improve the proper motions of the Tycho stars. In order to aid this work, the AC zones released by USNO have Tycho identifications, where applicable.
Three major reference star projects have been completed recently at the USNO: the Southern International Reference Stars (SIRS − 19, 827 stars) the southern part of the Faint Fundamentals (1,169 stars) and the Astrographic Catalog Reference Stars (ACRS - 325,416 stars). The compilation of the mean positions and proper motions of each is discussed. Reports on the progress of the USNO's Pole-to-Pole Fundamental Program and the Working Group on Star Lists are also presented.
A high density reference star catalog is being compiled at the U. S. Naval Observatory for the purpose of making new reductions of the Astrographic Catalog. The catalog will be a replacement to the SAO catalog and will be derived from the large photographic catalogs and the modern meridian circle catalogs. It is expected that the final catalog will contain 346, 000 stars, with proper motion mean errors generally or less, on a uniform system, the data having been reduced first to FK4 and then to FK5 using the International Reference Stars (IRS).
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