RSAA News of the Month: June 2003
Galactic Archaeology
Digging through the Fossil Record of the Milky Way
First light has been achieved for one of the most ambitious astronomy
projects ever undertaken on Australian soil. RAVE - the RAdial
Velocity Experiment - is an international consortium of twenty-one
astronomers from eleven countries. They will observe 100 nights per
year for the next two years at the 1.2m UK Schmidt Telescope,
located at Siding Spring Observatory, to
unveil the mysteries of how our Milky Way Galaxy formed. Professors
Ken Freeman (Mount Stromlo Observatory at
the Australian National
University), Brian Boyle (Anglo-Australian Observatory), and
Brad Gibson (Swinburne
University), are heading this ground-breaking research in
Australia.
Left: Siding Spring Observatory near Coonabarabran, NSW.
The site is owned and operated by the ANU. The ANU telescopes are
in the foreground. The largest dome houses the 3.9m Anglo-Australian
telescope; the UK Schmidt is in the left background. Since this image
was taken (in 1985) the University of NSW has also built a patrol
telescope on the site.
Right: The dome and offices of the UK Schmidt.
(Images: RSAA and UKSTU)
This unprecedented experiment will see radial
(i.e. line-of-sight) velocities and chemical compositions measured
for more than 100,000 stars - more than five times the number obtained
throughout the entire history of astronomy. These measurements carry
the tell-tale signatures of how our Milky Way Galaxy formed and how
the chemical elements were built. Excavating the history of the
Galaxy by carefully sifting through the wealth of RAVE data is like
archaeologists sifting through eons of historical data" notes
Prof Gibson. Galactic archaeology is perhaps the most important area
of astronomical research for the 21st century, guiding the development
of billion dollar facilities such as the European Space Agency's GAIA mission " states
Prof Boyle. Prof Freeman, the Australian representative on the RAVE
Executive Board, says that "Australia is uniquely poised to lead
the world in this cutting-edge research field".
The team will, for the first time, undertake a star-by-star
reconstruction of our Milky Way Galaxy. While surveys of the
extragalactic Universe have been undertaken before, no comparable
survey of our own Galaxy has ever been attempted, due to the
difficulty of sampling vast numbers of stars over the whole sky in a
reasonable allotment of observing time.
The halo of our Milky Way galaxy contains hundreds of smaller
satellite galaxies (image 1).
These have flown in along "spaghetti-like" tracks
(image 2), some surviving and some being torn apart
by the strong tides.
Searching the local environs of the Milky Way for the remains of
"cannibalized" satellite galaxies (image 3)
is the aim of the RAVE survey.
Images: computer simulations by Swinburne University
By combining the radial velocities with transverse (i.e. across the
line-of-sight) motions already measured from space by the Hipparcos satellite,
the RAVE science team will be able to identify hundreds of streams of
stars that represent disrupted old satellite galaxies now engulfed by
our Galaxy the fossil remains of the fundamental building blocks of
the Milky Way. Even after taking the plunge, the stars of the
now-disrupted building blocks retain some memory of their origin - the
memory can be extracted from the common velocities, movements and
chemical compositions possessed by the now-scattered stars. This
memory is retained even after billions of years. RAVE will be the
first survey of its kind to tap into this archaeological
record.
Left: Optical-fibre technician, Kristin Fiegert,
operating the robotic fibre-positioning system for 6dF.
Right: Prof Ken Freeman, Australian representative
on the RAVE Executive Board.
Images: UKSTU and Matthew Colless
Thanks to technological advances pioneered by engineers and
astronomers at the Anglo-Australian Observatory, the instrument
required to undertake such an all-sky survey is now a reality. Using
the unique 6dF (6-Degree
Field) Facility on the Schmidt Telescope at Siding Spring, near
Coonabarabran, NSW, the RAVE Team can now collect velocities for 150
stars simultaneously within a region of sky about 100 times the
apparent size of the full moon. This wide field capability allows the
RAVE Team to sample more than 100,000 stars over the whole sky in less
than three years. No other telescope on Earth is capable of
undertaking such an unprecedented survey. This latter statement is
all the more remarkable considering the modest size of the 1.2-metre
diameter Schmidt Telescope. In an era of giant telescopes, the UK
Schmidt Telescope and its wide field spectrometer provide a critical
opportunity for astronomers to exploit.
RSAA Contact: Prof Ken
Freeman, Research School of Astronomy and
Astrophysics, ANU
Astronomers participating in the RAVE project come from:
Australia:
The Research School of Astronomy and Astrophysics, ANU @
Mt Stromlo Observatory
Anglo-Australian Observatory
Swinburne University
Canada:
University of Victoria
France:
Observatoire de Paris
Germany:
Astrophysical Institute Potsdam
Astronomisches Rechen-Institut Heidelberg
Italy:
Astronomical Observatory of Padova
Japan:
National Astronomical Observatories of Japan
University of Tokyo
The Netherlands:
Utrecht University
Slovenia:
University of Ljubljana
Switzerland:
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 Rochester
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