‘RAVE’ to reveal Galaxy's history

Clues to how galaxies formed in the early Universe lie right under ournose - in our own Galaxy. The Galaxy formed by the accretion ofinfalling satellite galaxies, many astronomers think. Theoretical modelsof the formation of galaxies predict such a scenario.

But not all astronomers are convinced yet and the topic is stillcontroversial.

Now researchers from eleven countries have launched an ambitious projectto reconstruct our Galaxy's history by gathering key components ofmotion and chemical compositions for its apparently brightest 50 millionstars.

RAVE (RAdial Velocity Experiment) is an all-sky stellar spectroscopy survey just started on the 1.2-m UK Schmidt telescope in eastern Australia.

Projects such as Hipparcos and Tycho have accurately measured thepositions and proper motions - movement across the sky - of more than2.5 million stars.

But to get a complete picture of stellar motions, and thus to enable astronomers to reconstruct the structure and formation history of our Galaxy, they also need radial velocities - the movement of stars towards or away from the observer. And before RAVE began only about 20,000 stellar radial velocities were in the archives.

RAVE will be able to achieve velocities accurate to within 2 kms-1 -about 1% of the speed at which stars typically move in the Galaxy.

"With this accuracy and this number of radial velocities we will be able to identify dozens, perhaps hundreds, of streams of stars in the solarvicinity. The streams represent debris from disrupted old satellitegalaxies now engulfed by our Galaxy," said Professor Matthias Steinmetz,Director at the Astrophysical Institute Potsdam and leader of the RAVEscience team.

Even after plunging into our Galaxy, the stars of a satellite galaxycontinue to move as a coherent group, and can be identified by theircommon velocity even after billions of years. However, only a very fewof those disrupted satellites have been identified to date.

RAVE will also gather the chemical compositions of stars. These shouldhelp show which widely separated stars were formed at a common site. They should also determine whether these stars have been formed beforeor after the satellite galaxy of which they were a part broke up.

"RAVE will help us decide between competing models for the formation ofthe various structures of the Galaxy, such as the central bulge of starsand the so-called 'thick disk'," said Steinmetz.

"For a survey such as this, field of view is more important thanaperture. The UK Schmidt telescope is a perfect tool for this work,"said Professor Brian Boyle, Director of the Anglo-AustralianObservatory, which operates the telescope. The field of view of the UKSchmidt telescope covers an area more than 100 times larger than that ofthe Moon.

RAVE's initial pilot phase is being carried out with the 6dF (six-degreefield) instrument on the UK Schmidt. Designed and built by theAnglo-Australian Observatory, the 6dF instrument is a 'pick and place'robot that positions 150 fibres on the telescope's focal plane.

Using 6dF, astronomers can collect up to 600 stellar spectra per night.And by 2005 they plan to have 100,000 - five times as many as have beenmeasured since Hermann Carl Vogel started such work at the AstrophysicalObservatory Potsdam in 1888.

In 2006 the pace of data collection will pick up even further, when 6dF instrument is replaced by a radical new instrument from the AAO -UKidna, with 2250 fibres mounted on independently movable spines.

"With UKidna we'll be taking up to 22,000 spectra on a clear night,"said Boyle.

"Then we'll be able to push beyond our local Galactic neighbourhood, outinto the furthest corners of the Milky Way," said Professor Rosie Wyseof Johns-Hopkins University in Baltimore.

As well as uncovering the history of our Galaxy, RAVE will establish ahuge database of stellar spectra - by far the largest to date.

"This will be a vast resource for studies of the properties and evolution of stars," said Professor Ulisse Munari of the Padova Observatory in Asagio.

With its large database of stellar spectra RAVE will also provide anideal training set for the design of future space missions such as theEuropean Space Agency's cornerstone mission GAIA, which will attempt tomeasure positions and velocities of up to a billion stars in the Milky Way.


The Anglo-Australian Observatory operates the Anglo-Australian and UK Schmidt telescopes on behalf of the astronomical communities of the UK and Australia. The Observatory is funded by the UK Government, throughthe Particle Physics and Astronomy Research Council, and the Australian Government, through the Department of Education, Science and Training.






Helen Sim
Public Relations and Media Liaison
Anglo-Australian Observatory, Australia
Phone: +61 2-9372-4251   

Matthias Hassenpflug
Public Outreach
Astrophysikalisches Institut Potsdam, Germany
Phone: +49 331-7499-366

Brian Boyle
Anglo-Australian Observatory, Australia
Phone: +61 2-9372-4812   

Rosie Wyse
Johns-Hopkins University Baltimore, USA
Phone: +1 410-516-5392

Matthias Steinmetz
Astrophysikalisches Institut Potsdam, Germany
Phone: +49 331-7499-381   

Ulisse Munari
Padova Astronomical Observatory in Asiago, Italy
Phone: +39 0424-6000-33


The RAVE project involves researchers from:

Anglo-Australian Observatory, Mt-Stromlo Observatory, Swinburne
University, Macquarie University

University of Victoria

Observatoire de Strasbourg

Astrophysical Institute Potsdam, Astronomisches Rechen-Institut Heidelberg

Astronomical Observatory of Padova

National Astronomical Observatories of Japan, University of Tokyo

Kapteyn Astronomical Institute, University of Groningen

University of Ljubljana

University of Basel

United Kingdom
University of Cambridge, University of Oxford, University of Edinburgh

United States of America
University of Arizona, Johns-Hopkins University Baltimore, University of

Helen Sim
Public Relations and Media Liaison
CSIRO Australia Telescope National Facility (email: Helen.Sim@csiro.au)
Anglo-Australian Observatory (email: hsim@aaoepp.aao.gov.au)
National Organising Committee, IAU 25th General Assembly
Tel: +61-2-9372-4251
Mob: +61-419-635-905