RAVE (RAdial Velocity Experiment) is a multi-fiber

spectroscopic Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter ...

astronomical survey An astronomical survey is a general map or image of a region of the sky (or of the whole sky) that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of images, spectra, or other observations of ob ...

of stars in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...

using the 1.2-metre

UK Schmidt Telescope The UK Schmidt Telescope (UKST) is a 1.24 metre Schmidt telescope operated by the Australian Astronomical Observatory (formerly the Anglo-Australian Observatory); it is located adjacent to the 3.9 metre Anglo-Australian Telescope at S ...

of the

Australian Astronomical Observatory The Australian Astronomical Observatory (AAO), formerly the Anglo-Australian Observatory, was an optical and near-infrared astronomy observatory with its headquarters in North Ryde in suburban Sydney, Australia. Originally funded jointly by the ...

(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 The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

of stars from the observed spectra. Additional information is also derived such as

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. Effective temperature is often used as an estimate of a body's surface temperature ...

surface gravity The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as ...

, photometric

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. Due to foreshortening, nearby object ...

and elemental abundance data for the stars. 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.

Description

RAVE is an observational program in the field of Near Field

Cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosophe ...

which exploits our position inside the Milky Way to study its formation and evolution in greater detail than is possible for other

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

. 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 stellar halo of a galaxy refers to the component of its galactic halo containing stars. The halo extends far outside a galaxy's brightest regions and typically contains its oldest and most metal poor stars. Observation history Early studies, in ...

. The vast majority of stars in our Galaxy have no velocity measurements, and particularly no time-consuming radial velocity measurements. RAVE utilizes

fiber optics An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means ...

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 is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

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 In dynamical system theory, a phase space is a space in which all possible states of a system are represented, with each possible state corresponding to one unique point in the phase space. For mechanical systems, the phase space usual ...

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 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. It is usually denoted by \Delta\lambda, and is closely related to the resolvi ...

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 and from the Sun and so RAVE surveys halfway to the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ...

and halfway to the edge of the Galaxy's disk.

Observations

Since the end of the 6dF Galaxy Survey in 2004, the UK Schmidt telescope at

Siding Spring Siding Spring may refer to: * Siding Spring Observatory, an astronomical observatory in Australia ** Siding Spring 2.3 m Telescope, the telescope at Siding Spring Observatory ** Siding Spring Survey, a near-Earth object search program * 2343 Sidin ...

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 The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic longitudes of the Sun and Moon differ by 180°). This mean ...

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 A robot is a machine—especially one programmable by a computer—capable of carrying out a complex series of actions automatically. A robot can be guided by an external control device, or the control may be embedded within. Robots may be ...

-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 In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structural ...

and then recorded on a 1056 X 1027 CCD chip. An initial quality check of the data is performed at

Macquarie University Macquarie University ( ) is a Public university, public research university based in Sydney, Australia, in the suburb of Macquarie Park, New South Wales, Macquarie Park. Founded in 1964 by the New South Wales Government, it was the third univer ...

in Australia and the results are sent to the

University of Padova The University of Padua ( it, Università degli Studi di Padova, UNIPD) is an Italian university located in the city of Padua, region of Veneto, northern Italy. The University of Padua was founded in 1222 by a group of students and teachers fro ...

, Italy for

data reduction Data reduction is the transformation of numerical or alphabetical digital information derived empirically or experimentally into a corrected, ordered, and simplified form. The purpose of data reduction can be two-fold: reduce the number of data reco ...

. The reduced data is then sent to the

Leibniz Institute for Astrophysics Potsdam Leibniz Institute for Astrophysics Potsdam (AIP) is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory Potsdam (AOP) founded in 1874. The latter was the world's first ...

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 This is a list of stellar streams. A stellar stream is an association of stars orbiting a galaxy that was once a globular cluster or dwarf galaxy that has now been torn apart and stretched out along its orbit by tidal forces. An exception in the ...

, some of which are remnants of

dwarf galaxies A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

that merged with the Milky Way during

galaxy formation The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have gen ...

. A search for a stellar stream from the

Sagittarius Dwarf Elliptical Galaxy The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters ...

- which is currently merging with the Milky Way - in the vicinity of the sun yielded a

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 res ...

, which helps constrain the shape of the Milky Way's

dark halo According to modern models of physical cosmology, a dark matter halo is a basic unit of cosmological structure. It is a hypothetical region that has decoupled from cosmic expansion and contains gravitationally bound matter. A single dark ma ...

. Another study of the highest velocity stars was used to constrain the local Galactic

escape velocity In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non- propelled object to escape from the gravitational influence of a primary body, thus reaching an infinite distance from it. It is typically ...

and so the

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...

of the dark halo. RAVE is a precursor to

ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1 ...

Gaia mission ''Gaia'' is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until 2025. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented preci ...

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

VizieR A vizier (; ar, وزير, wazīr; fa, وزیر, vazīr), or wazir, is a high-ranking political advisor or minister in the near east. The Abbasid caliphs gave the title ''wazir'' to a minister formerly called '' katib'' (secretary), who was ...

catalog. Th
RAVE 4th Data Release
includes the radial velocities, stellar parameters (temperatures, gravities, metallicities), individual abundances and photometric parallaxes/distances as well as supplementary

photometry Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electrom ...

and

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Histor ...

for roughly 500 000 stars.

References

External links

RAVE survey

Australian Astronomical Observatory UK Schmidt Telescope homepage
{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Astronomical surveys Observational astronomy Siding Spring Observatory