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Post Info TOPIC: RAVE
Blobrana


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Posts: 131433
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RAVE Survey
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The RAVE Survey
Going six-dimensional (and more): Astrometry is giving positions, distances and proper motions of stars. The final dimension to fully define the motion of stars in the Galaxy is provided by RAVE.

* 2003-2005: 100,000 stars
* 2006-2012: up to 1,000,000 stars
* accuracy of velocity determination ~2 km/s
* stellar parameters
* distance estimates

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Blobrana


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Posts: 131433
Date:
RAdial Velocity Experiment
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Title: Distance determination for RAVE stars using stellar models II: Most likely values assuming a standard stellar evolution scenario
Authors: T. Zwitter (1 and 2), G. Matijevi\v{c) (1), M. A. Breddels (3), M. C. Smith (3, 4), A. Helmi (3), U. Munari (5), O. Bienaym\'{e) (6), J. Binney (7), J. Bland-Hawthorn (8), C. Boeche (9), A. G. A. Brown (10), R. Campbell (11), K. C. Freeman (12), J. Fulbright (13), B. Gibson (14), G. Gilmore (15), E. K. Grebel (16), J. F. Navarro (17), Q. A. Parker (18), G. M. Seabroke (19), A. Siebert (6), A. Siviero (5, 9), M. Steinmetz (9), F. G. Watson (20), M. Williams (9), R. F. G. Wyse (13) ((1) University of Ljubljana, Faculty of Mathematics, Physics, Ljubljana, Slovenia} (2) Center of excellence SPACE-SI, Ljubljana, Slovenia, (3) Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands, (4) Kavli Institute for Astronomy, Astrophysics, Peking University, Beijing, China, (5) INAF Astronomical Observatory of Padova,
36012 Asiago (VI), Italy, (6) Observatoire de Strasbourg, Strasbourg, France, (7) Rudolf Peierls Centre for Theoretical Physics, University of Oxford, UK, (8) Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia, (9) Astrophysikalisches Institut Potsdam, Potsdam, Germany, (10) Leiden Observatory, Leiden University, Leiden, The Netherlands, (11) Western Kentucky University, Bowling Green, Kentucky, USA, (12) RSAA, Australian National University, Canberra, Australia, (13) John Hopkins University, Baltimore, Maryland, USA, (14) University of Central Lancashire, Preston, UK, (15) Institute of Astronomy, Cambridge, UK, (16) ARI, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany, (17) University of Victoria, Victoria, Canada, (18) Macquarie University, Sydney, Australia, (19) e2v Centre for Electronic Imaging, Planetary, Space Sciences Research Institute, The Open University, Milton Keynes, UK, (20) Anglo Australian Observatory, Sydney, Australia)
et al. (36 additional authors not shown)

The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of the Milky Way. We use the subsample of spectra with spectroscopically determined values of stellar parameters to determine the distances to these stars. The list currently contains 235,064 high quality spectra which show no peculiarities and belong to 210,872 different stars. The numbers will grow as the RAVE survey progresses. The public version of the catalogue will be made available through the CDS services along with the ongoing RAVE public data releases.
The distances are determined with a method based on the work by Breddels et al.~(2010). Here we assume that the star undergoes a standard stellar evolution and that its spectrum shows no peculiarities. The refinements include: the use of either of the three isochrone sets, a better account of the stellar ages and masses, use of more realistic errors of stellar parameter values, and application to a larger dataset. The derived distances of both dwarfs and giants match within ~21% to the astrometric distances of Hipparcos stars and to the distances of observed members of open and globular clusters. Multiple observations of a fraction of RAVE stars show that repeatability of the derived distances is even better, with half of the objects showing a distance scatter of \simlt 11%.
RAVE dwarfs are ~300 pc from the Sun, and giants are at distances of 1 to 2 kpc, and up to 10 kpc. This places the RAVE dataset between the more local Geneva-Copenhagen survey and the more distant and fainter SDSS sample. As such it is ideal to address some of the fundamental questions of Galactic structure and evolution in the pre-Gaia era. Individual applications are left to separate papers, here we show that the full 6-dimensional information on position and velocity is accurate enough to discuss the vertical structure and kinematic properties of the thin and thick disks.

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Blobrana


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Posts: 131433
Date:
Local Galactic Escape Speed
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Title: The RAVE Survey: Constraining the Local Galactic Escape Speed
Authors: M.C. Smith, G.R. Ruchti, A. Helmi, R.F.G. Wyse, J.P. Fulbright, K.C. Freeman, J.F. Navarro, G.M. Seabroke, M. Steinmetz, M. Williams, O. Bienayme, J. Binney, J. Bland-Hawthorn, W. Dehnen, B.K. Gibson, G. Gilmore, E.K. Grebel, U. Munari, Q.A. Parker, R.-D. Scholz, A. Siebert, F.G. Watson, T. Zwitter

We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high velocity stars from the RAVE survey and two previously published datasets. We use cosmological simulations of disk galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 498\kms < \ve < 608 \kms (90 per cent confidence), with a median likelihood of 544\kms. The fact that \ve² is significantly greater than 2\vc² (where \vc=220\kms is the local circular velocity) implies that there must be a significant amount of mass exterior to the Solar circle, i.e. this convincingly demonstrates the presence of a dark halo in the Galaxy. For a simple isothermal halo, one can calculate that the minimum radial extent is ~58 kpc. We use our constraints on \ve to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of 1.42^{+1.14}_{-0.54}\times10^{12}M_\odot and virial radius of 305^{+66}_{-45} kpc (90 per cent confidence). For this model the circular velocity at the virial radius is 142^{+31}_{-21}\kms. Although our halo masses are model dependent, we find that they are in good agreement with each other.

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Blobrana


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Posts: 131433
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RE: RAVE
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Title: The Radial Velocity Experiment (RAVE): first data release
Authors: M. Steinmetz, T. Zwitter, A. Siebert, F.G. Watson, K.C. Freeman, U. Munari, R. Campbell, M. Williams, G.M. Seabroke, R.F.G. Wyse, Q.A. Parker, O. Bienayme, S. Roeser, B.K. Gibson, G. Gilmore, E.K. Grebel, A. Helmi, J.F. Navarro, D. Burton, C.J.P. Cass, J.A. Dawe, K. Fiegert, M. Hartley, K.S. Russell, W. Saunders, H. Enke, J. Bailin, J. Binney, J. Bland-Hawthorn, C. Boeche, W. Dehnen, D.J. Eisenstein, N.W. Evans, M. Fiorucci, J.P. Fulbright, O. Gerhard, U. Jauregi, A. Kelz, L. Mijovic, I. Minchev, G. Parmentier, J. Penarrubia, A.C. Quillen, M.A. Read, G. Ruchti, R.-D. Scholz, A. Siviero, M.C. Smith, R. Sordo, L. Veltz, S. Vidrih, R. von Berlepsch, B.J. Boyle, E. Schilbach

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution spectra (median R=7,500) in the Ca-triplet region ($\lambda\lambda$ 8,410--8,795 \AA) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9<I<12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including re-observations). Those data were obtained on 67 nights between 11 April 2003 to 03 April 2004. The total sky coverage within this data release is about 4,760 square degrees. The average signal to noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km/s. Combining internal errors and zero-point errors, the mode is found to be 2 km/s. Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km/s. We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with colour or signal to noise. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2 and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogues (Tycho-2, USNO-B, DENIS and 2MASS).

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Blobrana


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An international team of astronomers has released the first public data from the Radial Velocity Experiment, a spectroscopic survey aimed at measuring the speed, temperature, surface gravity and composition of up to a million stars near the sun.

The measurements, released at an astrophysics workshop at the Aspen Centre for Physics in Colorado, US, is available online.
It includes examination of old "fossil" stars that were born when our Milky Way galaxy was in its infancy. The data may eventually provide evidence to back up theories that our galaxy has -- over time -- "cannibalised" other, smaller galaxies and is "digesting" them.

http://www.rave-survey.aip.de/

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Blobrana


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Posts: 131433
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An international team of astronomers at The Johns Hopkins University, have announced the first results from the Radial Velocity Experiment (RAVE), an ambitious all-sky spectroscopic survey aimed at measuring the speed, temperature, surface gravity and composition of up to a million stars passing near the sun.

Those first results from the project, confirm that dark matter dominates the total mass of our home galaxy, the Milky Way. The full survey promises to yield a new, detailed understanding of the origins of the galaxy.

The results were released at the American Astronomical Society's 207th meeting in Washington, D.C.



The team is using the "six-degree field" multi-object spectrograph on the 1.2-m UK Schmidt Telescope at the Anglo-Australian Observatory, located at Siding Spring Observatory in New South Wales, Australia. The instrument is capable of obtaining spectroscopic information for as many as 150 stars at once.
RAVE includes members from the United States, Germany, Australia, Canada, the Netherlands, the United Kingdom, Slovenia, Italy, Switzerland and France.

"One important early application of RAVE aims to measure just how much stuff there is in our Milky Way galaxy — the collection of stars, gas and dark matter that is the home of our sun. Newton's Law of Gravity allows us to figure out from the orbital motions of stars how much mass is holding them together. Faster motions need more mass. We know from analysing the motions in other galaxies that there is a lot more mass than we can see and this dark matter appears to dominate. But we are not sure exactly how much dark matter is needed in our own galaxy, and we don't know what the dark matter is made up of. That information is important, and the RAVE survey is going to help us answer some of those questions" - Rosemary Wyse, professor in the Henry A. Rowland Department of Physics and Astronomy in Johns Hopkins' Krieger School of Arts and Sciences and a member of the RAVE team.

"The project needs large samples of very fast stars, and the unprecedented scope of the survey is ideal to find these rare objects. I'm really excited about being part of the RAVE team" -Greg Ruchti, graduate student in physics and astronomy at Johns Hopkins who also is a member of the RAVE team

With more data and more modelling, the RAVE team plans to ascertain the Milky Way's overall mass, which, at present, is poorly understood. The team has what it considers a "better approach" to the problem: a model that makes very definite predictions about the way mass varies as a function of distance from the centre of the Milky Way. If the team adopts this model, it can then estimate the overall mass from just the local "escape velocity," (500km/sec).

Escape velocity is the speed at which a star would have to be moving to leave the galaxy. The value of this special speed depends on the mass of the galaxy: the higher the mass, the higher the speed necessary to escape. Thus, researchers can estimate the weight of the Milky Way galaxy by measuring how fast objects must move to leave it.
Current RAVE limits show that stars would need to move faster than around 500 km/second to escape, more than twice as fast as the sun is moving around the galactic centre. At that escape speed, it would take less than eight seconds to travel from Baltimore to Los Angeles.

"Some groups believe that our neighbour, the Andromeda Galaxy — also known as M31 — is the most massive galaxy in our local group. But we suspect from our early results that our Milky Way is actually the local heavyweight. We are, with RAVE, on the verge of an answer" - Martin Smith of the University of Groningen in the Netherlands.

Funding for RAVE is provided by the National Science Foundation, for Johns Hopkins, and by the national research councils of other team members' countries as well as by private sources.

"RAVE will run for several more years, and the full RAVE survey will provide a vast resource of stellar motions and chemical abundances, allowing us to answer fundamental questions about the formation and evolution of our galaxy" - Matthias Steinmetz, director of the Astrophysical Institute Potsdam, and leader of the RAVE collaboration.

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-- Edited by Blobrana at 20:14, 2006-01-11

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