77 research outputs found
The Milky Way Tomography With SDSS. III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.NSF AST-615991, AST-0707901, AST-0551161, AST-02-38683, AST-06-07634, AST-0807444, PHY05-51164NASA NAG5-13057, NAG5-13147, NNXO-8AH83GPhysics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationMarie Curie Research Training Network ELSA (European Leadership in Space Astrometry) MRTN-CT-2006-033481Fermi Research Alliance, LLC, United States Department of Energy DE-AC02-07CH11359Alfred P. Sloan FoundationParticipating InstitutionsJapanese MonbukagakushoMax Planck SocietyHigher Education Funding Council for EnglandMcDonald Observator
The Milky Way Tomography with SDSS: III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence
stars with r<20 and proper-motion measurements derived from SDSS and POSS
astrometry, including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric parallax relation, covering a distance range from ~100 pc to 10 kpc
over a quarter of the sky at high Galactic latitudes (|b|>20 degrees). We find
that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the
rotational velocity for disk stars smoothly decreases, and all three components
of the velocity dispersion increase, with distance from the Galactic plane. In
contrast, the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the probed
volume. The velocity distribution of nearby ( kpc) K/M stars is complex,
and cannot be described by a standard Schwarzschild ellipsoid. For stars in a
distance-limited subsample of stars (<100 pc), we detect a multimodal velocity
distribution consistent with that seen by HIPPARCOS. This strong
non-Gaussianity significantly affects the measurements of the velocity
ellipsoid tilt and vertex deviation when using the Schwarzschild approximation.
We develop and test a simple descriptive model for the overall kinematic
behavior that captures these features over most of the probed volume, and can
be used to search for substructure in kinematic and metallicity space. We use
this model to predict further improvements in kinematic mapping of the Galaxy
expected from Gaia and LSST.Comment: 90 pages, 26 figures, submitted to Ap
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
The Milky Way Tomography with SDSS: II. Stellar Metallicity
Using effective temperature and metallicity derived from SDSS spectra for
~60,000 F and G type main sequence stars (0.2<g-r<0.6), we develop polynomial
models for estimating these parameters from the SDSS u-g and g-r colors. We
apply this method to SDSS photometric data for about 2 million F/G stars and
measure the unbiased metallicity distribution for a complete volume-limited
sample of stars at distances between 500 pc and 8 kpc. The metallicity
distribution can be exquisitely modeled using two components with a spatially
varying number ratio, that correspond to disk and halo. The two components also
possess the kinematics expected for disk and halo stars. The metallicity of the
halo component is spatially invariant, while the median disk metallicity
smoothly decreases with distance from the Galactic plane from -0.6 at 500 pc to
-0.8 beyond several kpc. The absence of a correlation between metallicity and
kinematics for disk stars is in a conflict with the traditional decomposition
in terms of thin and thick disks. We detect coherent substructures in the
kinematics--metallicity space, such as the Monoceros stream, which rotates
faster than the LSR, and has a median metallicity of [Fe/H]=-0.96, with an rms
scatter of only ~0.15 dex. We extrapolate our results to the performance
expected from the Large Synoptic Survey Telescope (LSST) and estimate that the
LSST will obtain metallicity measurements accurate to 0.2 dex or better, with
proper motion measurements accurate to ~0.2 mas/yr, for about 200 million F/G
dwarf stars within a distance limit of ~100 kpc (g<23.5). [abridged]Comment: 40 pages, 21 figures, emulateApJ style, accepted to ApJ, high
resolution figures are available from
http://www.astro.washington.edu/ivezic/sdss/mw/astroph0804.385
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