RAVE (survey)
The RAdial Velocity Experiment ( RAVE ) is a spectroscopic survey of the southern sky. To this end, a multi-object spectrograph on the 1.2 m UK Schmidt Telescope of the Anglo - Australian Observatory (Australia) is being used. RAVE is a joint project of scientists from over 20 institutions around the world, led by the Leibniz Institute for Astrophysics Potsdam ( AIP).
The main objective of RAVE is to measure the radial velocities of a representative number of stars of almost the entire southern hemisphere taking advantage of the Doppler effect. Also further properties of the stars are obtained from the recorded spectra, namely the effective temperature, surface gravity and metallicity. Furthermore, photometric parallax (distance measurements) and frequencies were determined by individual chemical elements.
The project started in 2003 and until the end of the data collection phase on April 5, 2013 574 630 483 330 spectra of stars were recorded.
Description
RAVE is a monitoring program as part of the so-called near-field cosmology (also: Galactic Archaeology ). This branch of astrophysics is concerned with the formation and evolution of galaxies in the example of our home galaxy, the Milky Way. This exploits the fact that the earth is to be examined within the system and thus allows the large-scale structures dissolve into individual stars. For the vast majority of the speeds star but are unknown, and in particular there is no time-consuming radial velocity measurements. The RAVE project tries to fill this gap. For an optical fiber is used to take each observation run up to 150 stellar spectra simultaneously. In this way in a relatively short time, a representative sample of nearby stars for almost half of the celestial sphere are measured. Most of the stars of the catalog are 1500-13000 light years away from the Sun, which corresponds to about half the distance to the Galactic center and the edge of the Galactic disk.
For the majority of the measured RAVE stars and proper motion data is available. If the distance to a star known (eg via a photometric parallax by means of the RAVE spectra ), one can calculate the transverse velocity of the proper motion and thus knows all six phase space coordinates. These are needed for many questions about the history of our Milky Way.
Similar projects
RAVE is complementary to the SEGUE project, a sub-program of the Sloan Digital Sky Survey (SDSS ). While RAVE screened the southern sky, with an average depth of observation ( exposure) and medium spectral resolution SEGUE watched the northern sky (more precisely selected portions thereof) with long exposure times and low spectral resolution for this but with high spectral bandwidth.
RAVE can also be viewed as a precursor of the satellite mission Gaia, which demonstrates the scientific potential of this milestone project of the European Space Agency ( ESA).
The observations
Since the conclusion of 6dF Galaxy Survey in 2004, the UK Schmidt telescope is fully dedicated to the RAVE survey. Before that there was already a pilot phase ( April 2003-April 2004 ) in the was available only during the nights around full moon time of observation. The telescope is particularly suitable for spectroscopic sky surveys such as RAVE as through the wide field of view ( 6 -degree beam angle) comparatively large parts of the sky can be observed simultaneously and with the multi-object spectrograph " 6dF " ( " 6 degree field" ) is already a suitable detector is available.
The 6dF instrument is operated with three (initially two) interchangeable so-called field plates. These are introduced for each observation runs in the focal plane of the telescope. Before the robot has positioned the ends of up to 150 optical fibers of the plate and in each case so that the light from a single star is directed into the selected optical fiber. The robot achieves a positioning accuracy of 10 micrometers. Because multiple field plates are present, each plate can be reconfigured by the robot while watching another.
The light of the selected stars is headed by the glass fibers in the actual spectrograph where it is split by a diffraction grating to be recorded ( 1027 pixels x 1056 ) and ending of a CCD chip.
The detected spectra are then subjected at Macquarie University in Australia a first quality test. If this were they will continue to be sent to the University of Padua (Italy ) where the data reduction ( extracting the actual star spectrum from the digital "photography" ) takes place. The final product of this procedure eventually ends up at the Astrophysical Institute Potsdam, where the actual data analysis, ie, the extraction of the radial velocity and the other characteristic parameters of the star, is performed.
Results
Studies that use the RAVE data usually deal either with unusual stars or objects or with large-scale trends in the various components of our galaxy. In the latter, the main interest is on the structure and formation of the Galaxy.
An important example is the search for star streams. One suspects for a portion of this that they are remnants of dwarf galaxies that are fused during the development phase of the Milky Way with her. A search of the stellar stream from the Sagittarius dwarf galaxy, which is currently in the merger process led to no result, but this helped to better demarcate the shape of the dark halo of the Milky Way a.
Another study used the fastest stars in the RAVE catalog to the local Galactic escape velocity and thus to determine the mass of the Milky Way.
Data Access
The RAVE data are accessible via the RAVE Web server or the Vizier catalog. In both sources, additional information such as photometry and astrometry data are included. In a separate catalog and photometric parallaxes (distances so ) are available.