Galactic Archaeology: A Radial Velocity Experiment to Unveil the History of the Milky Way – RAVE

RAVE (RAdial Velocity Experiment) is an ongoing and ambitious program to measure precise radial velocities and chemical abundances of a million nearby stars, using the UK Schmidt Telescope and the 6dF multi-object fibre spectrometer at Siding Spring Observatory (Australia). RAVE will be a giant leap forward in our understanding of our Milky Way Galaxy, providing a vast database of stellar kinematics and chemical abundances, two orders of magnitude larger than any comparable survey. RAVE will offer the first truly representative inventory of stellar radial velocities for the disk and halo of the Galaxy. Its scope and homogeneity will make it an invaluable stand-alone resource, but its full potential will be realised when the radial velocities are combined with proper motions and parallaxes from other sources, including the European astrometric space mission GAIA (http://astro.estec.esa.nl/GAIA/). RAVE will also provide a huge database of stellar chemical properties, which will be invaluable for more detailed chemical investigations. The RAVE survey is the ideal resource for a large program to identify stars that formed in common aggregates or clusters as the galactic disk evolved, using the new methods of chemical tagging (Freeman & Bland-Hawthorn 2002). The sample of precise stellar velocities and chemical abundances from the RAVE survey will be large enough to identify, for the first time, the remains of the small galaxies and star clusters which were the ancient building blocks of our Galaxy but have in the meantime broken up and dispersed. This will be «near-field cosmology» in action. From the RAVE database of a million stars, we can also derive the definitive relationship between stellar age, random velocities and metallicity in the solar vicinity. This is crucial input for understanding how the Galaxy evolved chemically and dynamically. RAVE began in 2003 with a pilot survey. This pilot program, of 100,000 stars, was aimed at testing the adequacy of the instrument and determining the strategy for sample selection, observing, data analysis and archiving for the main RAVE survey, which is scheduled to run from 2006 to 2011. The pilot survey used 5 nights of telescope time per month for about 2.5 years and was very successful. The quality of the spectra and the accuracy of the stellar velocities (2 km/s) are fully up to expectation. In February 2006, the first public data release was made and the first scientific papers submitted. The pilot survey has already skimmed off some exciting scientific results, including discovery of many new stars in the Arcturus moving group (a likely remnant of a small galaxy which fell into the Milky Way), and a new estimate of the total mass of our Galaxy from new RAVE stars with extreme velocities (Williams et al 2005, Ruchti et al 2005). RAVE spectra also provide a spectacular demonstration of how the _ambda862 nm diffuse interstellar band can be used to measure the interstellar absorption to individual stars: this is an ever-present problem in stellar and galactic astrophysics (Munari et al 2005). Our first survey and science results were presented in a series of 8 papers under the RAVE banner at the American Astronomical Society meeting in January 2006. The RAVE pilot survey has demonstrated beyond doubt the feasibility and scientific opportunities of the main RAVE survey. The scientific opportunities became obvious to many, and RAVE rapidly evolved into a large collaboration of astronomers from Australia, Canada, France, Germany, Italy, The Netherlands, Slovenia, Switzerland, UK and US (see www.aip.de/RAVE). To hold our place in this exciting collaboration and maintain our influential role on its scientific directions, the french RAVE team members need to remain in all aspects of the RAVE program. Due to the substantial foreign investment, RAVE acquired full-time use of the telescope at cost and made the transition from the pilot survey to the main survey of one million stars. (The main RAVE survey will now be done with the existing robotic positioner 6dF). The international RAVE consortium pays the AAO for telescope time and technical support and contributes postdocs and students. This proposal is to fund one postdoc to support share of the technical and scientific effort.