DivA: Fundamental Astronomy
IAU Division A gathers astronomers studying a wide range of problems related to fundamental physical phenomena, such as time, inertial reference frames, positions and proper motions of celestial objects and the precise dynamical computation of motions of celestial bodies in planetary, stellar and galactic systems. It is always concerned with the same basic problems, but the solutions are constantly being reconsidered and revised thanks to new observational data.
While this work may not seem particularly spectacular or newsworthy, it plays a fundamental contribution to astronomy — and it is often extremely challenging. The collection of new observations, improvements in standards, revisions of existing models and huge theoretical and computational simulations are only possible with an interdisciplinary approach and the collaboration of other IAU Divisions.
For Division A, the most spectacular and popular astrometry mission is certainly Gaia, involving a huge international team. But let’s not forget JASMINE (Japan Astrometry Satellite Mission for Infrared Exploration) and some other exciting missions in the works.
The observational activity of Division A is not limited to space missions; it also involves traditional ground-based observations, using telescopes and cameras that just keep getting better. Optical, infrared, and radio astrometry campaigns and systematic surveys are developed every year and contribute substantially to the flood of new ground-based data.
Besides collecting observations, Division A also develops models and theories and performs numerical simulations necessary to interpret data, improve our knowledge and to understand unexpected findings.
Organisation of Division A
Division A coordinates a wide range of scientific activity, mainly performed within the five Commissions:
- Three Commissions are intrinsically linked to the history and core of Division A: Commission A1, Astrometry; Commission A2, Rotation of the Earth and Commission A3, Fundamental Standards.
- Inter-Division Commission A4, Celestial Mechanics and Dynamical Astronomy, belongs primarily to Division A for its methodology and approach, but also to Division F, Planetary Systems and Bioastronomy, for the physical properties of the bodies involved in the models.
- Cross-Division Commission X2, Solar System Ephemerides, is a thoroughly interdisciplinary group, drawing again from the members of Divisions A and F.
Division A also hosts eight functional (permanent) Working Groups:
- Numerical Standards in Fundamental Astronomy (NSFA), Standards of Fundamental Astronomy (SOFA), Time Metrology Standards (TMS) and, again in partnership with Division F, Cartographic Coordinates and Rotational Elements (CCRE). These bodies are not linked to particular well-identified problems. Their mission is to improve standards, propose the adoption of more precise constants and inform the scientific community about those standards and their limits.
- Three classical Working Groups show the dynamism of the Commissions to propose thought-worthy discussions, to create international groups of experts and to deal with urgent questions and document their answers. This is the case for Third Realisation of the International Celestial Reference Frame (ICRF3), Astrometry by Small Ground-Based Telescopes (ASGB) and Multi-waveband Realisations of International Celestial Reference System (ICRS).
- Theory of Earth Rotation and Validation (TERV), is a joint Working Group of the IAU (organised under Commission A2) and the International Association of Geodesy (IAG).
All Division A Commissions and Working Groups have excellent Organising Committees and show, through their annual and triennial reports, their strong scientific activity and investment in modern astronomy.
General Assembly Scientific Programme for Division A
The scientific community, both within and beyond the membership of Division A, are invited to Symposium 348, 21st Century Astrometry: Crossing the Dark and Habitable Frontiers at the GA (28–31 August). Its challenge is to connect precisely all of the new celestial and terrestrial reference frames relevant to improving our understanding of Earth’s rotation. A new astrometry framework has to be designed that combines past and future data.
Division A will devote the scientific content of our Division Meeting to the topics covered by the two other proposals originally submitted for the GA. On 27 August we will welcome two sessions: one about the space mission Gaia and another about reference frames. Both sessions will feature experts in the fields: T. Prusti, A. Brown, L. Lindegren, P. Tanga and A. Vallenari for Gaia, and P. Charlot, F. Mignard, Z. Altamimi and R. Heinkelmann for reference frames. We’ll have a large common poster session associated with the talks.
A third topic was also proposed, concerning the dynamics of small bodies in the Solar System and in exoplanetary systems, in the framework of new models in celestial mechanics. However, rather than organising parallel and redundant sessions, Division A decided to join Division F on 24 August for a joint Planet Days session, with speakers representing both Divisions.
As a sign of the dynamism of Division A, almost all our Commissions and Working Groups will hold business meetings during the General Assembly. These are concentrated during the second week (27‒29 August), in parallel with Symposium 348, to allow maximum participation. Furthermore, the idea of a PhD prize to motivate young scientists to participate in IAU meetings and other Union activities was well received by Division A, and our first PhD prize, for 2017, goes to Gisela Ortiz Leon for her work on ultra-high-precision astrometry with centimetre- and millimetre-wavelength very-long-baseline interferometry. The prize will be presented to the laureate on 27 August, at the end of the scientific session.
ANNE LEMAÎTRE conducts research in celestial mechanics at the University of Namur, Belgium, where she is a professor in the Department of Mathematics and at the research institute naXys (Namur Institute for Complex Systems) as well as Dean of the Faculty of Sciences.