RAdial Velocity Experiment

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The Radial Velocity Experiment ( RAVE ) is a spectroscopic survey of the southern sky . For this one is multi-object - spectrograph on the 1.2-meter UK Schmidt Telescope of the Anglo-Australian Observatory ( Australia used). RAVE is a joint project of scientists from over 20 institutions worldwide under the leadership of the Leibniz Institute for Astrophysics Potsdam (AIP).

The main objective of RAVE is to measure the radial velocities of a representative number of stars from almost the entire southern hemisphere using the Doppler effect . Other properties of the stars are also obtained from the recorded spectra, namely the effective temperature , surface gravity and metallicity . In addition, photometric parallaxes ( distance measurements ) and frequencies of individual chemical elements were determined.

The project started in 2003 and by the end of the data collection phase on April 5, 2013, 574,630 spectra of 483,330 stars had been recorded.

description

RAVE is an observation program within the so-called near-field cosmology (also: galactic archeology). This branch of astrophysics deals with the formation and development of galaxies using the example of our home galaxy, the Milky Way . This makes use of the fact that the earth is located within the system to be investigated and thus the large-scale structures can be broken down into individual stars. For the vast majority of stars, however, the velocities are unknown and, in particular, there are no time-consuming radial velocity measurements. The RAVE project tries to close this gap. For this purpose, fiber optics are used to simultaneously record up to 150 star spectra per observation run . In this way, in a relatively short time, a representative sample of nearby stars can be measured for almost half of the celestial sphere. Most of the stars in the catalog are between 1,500 and 13,000 light-years from the Sun, which is roughly half the distance from the galactic center and the edge of the galactic disk .

Self- motion data is also available for the majority of the stars measured by RAVE . If the distance to a star is also known (e.g. via a photometric parallax using the RAVE spectra), the transverse velocity can be calculated from the proper movement and thus all six phase space coordinates are known . These are needed for many questions about the history of our Milky Way galaxy.

Similar projects

RAVE is complementary to the SEGUE project, a sub-program of the Sloan Digital Sky Survey (SDSS). While RAVE scans the southern sky with medium observation depth (exposure times) and medium spectral resolution, SEGUE observes the northern sky (more precisely: selected parts of it) with long exposure times and low spectral resolution, but with a high spectral bandwidth.

RAVE can also be seen as the forerunner of the Gaia satellite mission , which shows the scientific potential of this milestone project of the European Space Agency (ESA).

The observations

Since the completion of the 6dF Galaxy Survey ("6dF" from 6 degree field '6 degree field' ) in 2004, the UK Schmidt telescope has been fully dedicated to RAVE surveys. Before that there was already a pilot phase (April 2003 to April 2004) in which observation time was only available during the nights around the full moon . The telescope is particularly suitable for spectroscopic sky surveys such as RAVE, as the wide field of view (opening angle of 6 °) allows comparatively large parts of the sky to be observed at the same time and the multi-object spectrograph "6dF" already has a suitable detector.

The 6dF instrument is operated with three (initially two) exchangeable so-called field plates. These are brought into the focal plane of the telescope for the individual observation runs. Previously, a robot positioned the ends of up to 150 optical fibers on the plate, each in such a way that the light from a single selected star is guided into the optical fiber. The robot achieves a positioning accuracy of 10 micrometers. Since there are several field plates, one plate at a time can be reconfigured by the robot while another is being observed.

The light from the selected stars is guided by the glass fibers into the actual spectrograph, where it is split up by a diffraction grating and finally picked up by a CCD chip (1056 × 1027 pixels).

The detected spectra are then subjected to an initial quality test at Macquarie University in Australia. If this is passed, they are sent to the University of Padua (Italy) where the data reduction (extraction of the actual star spectrum from the digital "photography") takes place. The end product of this procedure ends up at the Astrophysical Institute in Potsdam, where the actual data evaluation, i.e. the extraction of the radial velocity and the other characteristic parameters of the stars, is carried out.

Results

Studies using the RAVE data mostly deal either with unusual stars or objects or with large-scale trends in the various components of our galaxy. In the latter case, the main interest lies in the structure and formation of the Milky Way.

Another important example is the search for star currents . Some of these are believed to be the remains of dwarf galaxies that merged with the Milky Way during the formation phase. A search for the star stream from the Sagittarius dwarf galaxy, which is currently in the merger process, did not lead to any result, but this helped to better narrow down the shape of the dark halo of the Milky Way.

Another study used the fastest stars in the RAVE catalog to determine the local galactic escape speed and thus the mass of the Milky Way.

Data access

The RAVE data can be accessed via the RAVE web server or via the VizieR catalog. Both sources also contain additional information such as photometry and astrometry data. Photometric parallaxes (i.e. distances) are also available in a separate catalog.

See also

Web links

Individual evidence

  1. ^ RAVE - the Radial Velocity Experiment. In: rave-survey.aip.de. Retrieved on April 12, 2013 (English): "April 2013: on April 5, 2013 RAVE concluded its phase of data taking. In an almost ten year observing campaign, a total of 574,630 spectra have been obtained on 483,330 individual stars by a small team of AAO observers, with other observers making occasional visits from RAVE participating institutions. "
  2. ↑ Steinmetz et al .: RAVE fist data release . In: The Astronomical Journal . 2006. bibcode : 2006AJ .... 132.1645S .
  3. ↑ Seabroke et al .: Is the sky falling? Searching for stellar streams in the local Milky Way disc in the CORAVEL and RAVE surveys . In: Monthly Notices of the Royal Astronomical Society . 2008. bibcode : 2008MNRAS.384 ... 11S .
  4. ^ Smith et al .: The RAVE survey: constraining the local Galactic escape speed . In: Monthly Notices of the Royal Astronomical Society . 2007. bibcode : 2007MNRAS.379..755S .
  5. ↑ RAVE data access . Retrieved September 18, 2010.
  6. ↑ RAVE data on VizieR . Retrieved September 18, 2010.
  7. ↑ Breddels et al .: RAVE DR2 distance catalog . In: VizieR On-line Data Catalog . 2010. bibcode : 2010yCat..35119090B .