RAVE (survey)
Encyclopedia
RAVE is a multi-fiber spectroscopic astronomical survey of stars in the Milky Way
using the 1.2-metre UK Schmidt Telescope
of the Anglo-Australian Observatory
(AAO). The RAVE collaboration consists of researchers from over 20 institutions around the world and is coordinated by the Leibniz Institute for Astrophysics Potsdam (AIP).
As a southern hemisphere
survey covering 20,000 square degrees of the sky, RAVE's primary aim is to derive the radial velocity
of stars from the observed spectra. Additional information is also derived such as effective temperature
, surface gravity
, metallicity
, photometric parallax
and elemental abundance data for the stars.
Beginning in 2003, RAVE had obtained 450,000 observations of stars to mid-2010. It is expected to run to the end of 2012.
which exploits our position inside the Milky Way to study its formation and evolution in greater detail than is possible for other galaxies. RAVE focuses on obtaining stellar radial velocities to study the motions of stars in the Milky Way's thin and thick disk and stellar halo. The vast majority of stars in our Galaxy has no velocity measurements, and particularly no time-consuming radial velocity measurements. RAVE utilizes fiber optics to perform multiple, simultaneous spectroscopy on up to 150 stars in a single observation. In this way it can obtain a representative sample of the nearby stars in our Galaxy which are all around, over a wide area of the sky.
For the majority of RAVE stars proper motion
data is also available. Combining the proper motions with distances derived using the photometric parallax method
, the transverse velocity of these stars can be calculated. With the observed radial velocities the full 6D phase space
information for the stars is then obtainable.
RAVE is complementary to the SDSS
project's SEGUE program as it a southern hemisphere, wide-field, intermediate-depth, intermediate spectral resolution
survey with limited wavelength coverage. Conversely, SEGUE is a northern hemisphere survey with selected angular coverage, deep exposures, low-resolution but large wavelength coverage.
Most of the stars observed by RAVE are between 1500 and 13000 light years
from the sun and so RAVE surveys halfway to the Galactic center
and halfway to the edge of the Galaxy's disk.
in 2004, the UK Schmidt telescope at Siding Spring has been dedicated to the RAVE survey. This followed the first year of the pilot phase of the survey (April 2003 - April 2004), where RAVE observed around the full moon
period. RAVE exploits the wide field-of-view of the UK Schmidt (6 degrees on the sky) as well as the capabilities of the UK Schmidt's 6dF instrument.
The multi-object spectrograph 6dF (6 degree Field) utilizes interchangeable field plates with robot
-positional optical fibers, with 150 fibers each . Each fiber is attached to a `button' which is positioned by the robot (to a precision of 10 micrometres) in order to capture the light from one target star. Once the field plate is configured it matches the pattern of stars on the sky that it is observing. Three field plates are available, which means that one plate can be configured by the robot while another is being used in the telescope. From the telescope the light is sent down the optical fibers to the spectrograph unit to be dispersed through a diffraction grating
and then recorded on a 1056 X 1027 CCD
chip.
An initial quality check of the data is performed at Macquarie University
in Australia and the results are sent to the University of Padova, Italy for data reduction
. The reduced data is then sent to the Leibniz Institute for Astrophysics Potsdam in Germany for final extraction of the radial velocities and the other stellar parameters.
- which is currently merging with the Milky Way - in the vicinity of the sun yielded a null result
, which helps constrain the shape of the Milky Way's dark halo . Another study of the highest velocity stars was used to constrain the local Galactic escape velocity
and so the mass
of the dark halo .
RAVE is a precursor to ESA's Gaia mission and studies with RAVE show the science potential of this upcoming survey of stars in the Milky Way.
catalog . The catalog includes supplementary photometry
and astrometry
. Currently, the radial velocities and stellar parameters (temperatures, gravities, metallicities) are available in the catalog. Photometric parallaxes/distances are available separately derived from the stellar parameters and photometry.
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
using the 1.2-metre UK Schmidt Telescope
UK Schmidt Telescope
The 1.2 metre UK Schmidt Telescope is operated by the Australian Astronomical Observatory , and located adjacent to the 3.9 metre Anglo-Australian Telescope at Siding Spring Observatory, Australia...
of the Anglo-Australian Observatory
Anglo-Australian Observatory
The Australian Astronomical Observatory , formerly the Anglo-Australian Observatory, is an optical/near-infrared astronomy observatory with its headquarters in suburban Sydney, Australia...
(AAO). The RAVE collaboration consists of researchers from over 20 institutions around the world and is coordinated by the Leibniz Institute for Astrophysics Potsdam (AIP).
As a southern hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
survey covering 20,000 square degrees of the sky, RAVE's primary aim is to derive the radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
of stars from the observed spectra. Additional information is also derived such as effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...
, surface gravity
Surface gravity
The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface. The surface gravity may be thought of as the acceleration due to gravity experienced by a hypothetical test particle which is very close to the object's surface and which, in...
, metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
, photometric parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...
and elemental abundance data for the stars.
Beginning in 2003, RAVE had obtained 450,000 observations of stars to mid-2010. It is expected to run to the end of 2012.
Description
RAVE is an observational program in the field of Near Field CosmologyCosmology
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...
which exploits our position inside the Milky Way to study its formation and evolution in greater detail than is possible for other galaxies. RAVE focuses on obtaining stellar radial velocities to study the motions of stars in the Milky Way's thin and thick disk and stellar halo. The vast majority of stars in our Galaxy has no velocity measurements, and particularly no time-consuming radial velocity measurements. RAVE utilizes fiber optics to perform multiple, simultaneous spectroscopy on up to 150 stars in a single observation. In this way it can obtain a representative sample of the nearby stars in our Galaxy which are all around, over a wide area of the sky.
For the majority of RAVE stars proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
data is also available. Combining the proper motions with distances derived using the photometric parallax method
Photometric parallax method
The photometric parallax method is a method of data analysis used in astronomy that uses the colours and apparent brightnesses of stars to infer their distances...
, the transverse velocity of these stars can be calculated. With the observed radial velocities the full 6D phase space
Phase space
In mathematics and physics, a phase space, introduced by Willard Gibbs in 1901, is a space in which all possible states of a system are represented, with each possible state of the system corresponding to one unique point in the phase space...
information for the stars is then obtainable.
RAVE is complementary to the SDSS
SDSS
SDSS may refer to:* Sloan Digital Sky Survey, a major multi-filter imaging and spectroscopic redshift survey* Social Democratic Party of Slovakia* Spatial Decision Support System, a GIS based decision aiding system...
project's SEGUE program as it a southern hemisphere, wide-field, intermediate-depth, intermediate spectral resolution
Spectral resolution
The spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum...
survey with limited wavelength coverage. Conversely, SEGUE is a northern hemisphere survey with selected angular coverage, deep exposures, low-resolution but large wavelength coverage.
Most of the stars observed by RAVE are between 1500 and 13000 light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
from the sun and so RAVE surveys halfway to the Galactic center
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
and halfway to the edge of the Galaxy's disk.
Observations
Since the end of the 6dF Galaxy Survey6dF Galaxy Survey
The 6dF Galaxy Survey , 6dF or 6dFGS is a redshift survey conducted by the Anglo-Australian Observatory with the 1.2m UK Schmidt Telescope between 2001 and 2009. The data from this survey were made public on 31 March 2009. The survey has mapped the nearby universe over nearly half the sky...
in 2004, the UK Schmidt telescope at Siding Spring has been dedicated to the RAVE survey. This followed the first year of the pilot phase of the survey (April 2003 - April 2004), where RAVE observed around the full moon
Full moon
Full moon lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. More precisely, a full moon occurs when the geocentric apparent longitudes of the Sun and Moon differ by 180 degrees; the Moon is then in opposition with the Sun.Lunar eclipses can only occur at...
period. RAVE exploits the wide field-of-view of the UK Schmidt (6 degrees on the sky) as well as the capabilities of the UK Schmidt's 6dF instrument.
The multi-object spectrograph 6dF (6 degree Field) utilizes interchangeable field plates with robot
Robot
A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
-positional optical fibers, with 150 fibers each . Each fiber is attached to a `button' which is positioned by the robot (to a precision of 10 micrometres) in order to capture the light from one target star. Once the field plate is configured it matches the pattern of stars on the sky that it is observing. Three field plates are available, which means that one plate can be configured by the robot while another is being used in the telescope. From the telescope the light is sent down the optical fibers to the spectrograph unit to be dispersed through a diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
and then recorded on a 1056 X 1027 CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
chip.
An initial quality check of the data is performed at Macquarie University
Macquarie University
Macquarie University is an Australian public teaching and research university located in Sydney, with its main campus situated in Macquarie Park. Founded in 1964 by the New South Wales Government, it was the third university to be established in the metropolitan area of Sydney...
in Australia and the results are sent to the University of Padova, Italy for data reduction
Data reduction
Data Reduction is the transformation of numerical or alphabetical digital information derived empirical or experimentally into a corrected, ordered, and simplified form....
. The reduced data is then sent to the Leibniz Institute for Astrophysics Potsdam in Germany for final extraction of the radial velocities and the other stellar parameters.
Results
Studies from RAVE either concentrate on peculiar stars and objects or overall trends for the different components of our Galaxy, with a main focus of the structure and formation of the Milky Way. For example, RAVE is suited to searching for stellar streams, some of which are remnants of dwarf galaxies that merged with the Milky Way during galaxy formation. A search for a stellar stream from the Sagittarius Dwarf Elliptical GalaxySagittarius Dwarf Elliptical Galaxy
The Sagittarius Dwarf Elliptical Galaxy is an elliptical loop-shaped satellite galaxy of the Milky Way Galaxy. It consists of four globular clusters, the main cluster being discovered in 1994...
- which is currently merging with the Milky Way - in the vicinity of the sun yielded a null result
Null result
In science, a null result is a result without the expected content: that is, the proposed result is absent. It is an experimental outcome which does not show an otherwise expected effect. This does not imply a result of zero or nothing, simply a result that does not support the hypothesis...
, which helps constrain the shape of the Milky Way's dark halo . Another study of the highest velocity stars was used to constrain the local Galactic escape velocity
Escape velocity
In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
and so the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the dark halo .
RAVE is a precursor to ESA's Gaia mission and studies with RAVE show the science potential of this upcoming survey of stars in the Milky Way.
Data access
RAVE data is available from the RAVE web server or from the VizieRVizieR
The VizieR Catalogue Service is an astronomical catalog service provided by Centre de données astronomiques de Strasbourg.The origin of the ViZieR Catalogue Service dates back to 1993 as the ESA European Space Information System Catalogue Browser...
catalog . The catalog includes supplementary photometry
Photometry
Photometry can refer to:* Photometry , the science of measurement of visible light in terms of its perceived brightness to human vision...
and astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
. Currently, the radial velocities and stellar parameters (temperatures, gravities, metallicities) are available in the catalog. Photometric parallaxes/distances are available separately derived from the stellar parameters and photometry.
See also
- Milky WayMilky WayThe Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
- SDSSSDSSSDSS may refer to:* Sloan Digital Sky Survey, a major multi-filter imaging and spectroscopic redshift survey* Social Democratic Party of Slovakia* Spatial Decision Support System, a GIS based decision aiding system...
- Gaia mission
- UK Schmidt TelescopeUK Schmidt TelescopeThe 1.2 metre UK Schmidt Telescope is operated by the Australian Astronomical Observatory , and located adjacent to the 3.9 metre Anglo-Australian Telescope at Siding Spring Observatory, Australia...
Further reading
- RAVE-ING Success As Generations Of Astronomers Survey The Stars, physorg.com
- Galactic archaeology: Overcoming great barriers by Timothy C. Beers & Daniela Carollo, Nature