'RAVE' seeking to reveal Galaxy's historyJun 04, 2003( taken from SpaceFlightNow ) |
 Modeler's view of our Milky Way Galaxy -- at the center -- in a lumpy halo with many satellites. Photo: NASA. Simulation: Stefan Gottlober/AIP |
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 spectroscopysurvey 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 enableastronomers to reconstruct the structure and formation history of ourGalaxy, they also need radial velocities - the movement of stars towardsor away from the observer. And before RAVE began only about 20,000stellar 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 ableto 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 6dFinstrument 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 andevolution of stars," said Professor Ulisse Munari of the PadovaObservatory 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 UKSchmidt telescopes on behalf of the astronomical communities of the UKand Australia. The Observatory is funded by the UK Government, throughthe Particle Physics and Astronomy Research Council, and the AustralianGovernment, through the Department of Education, Science and Training.