|
Bright plate |
One of two plates centered on a particular direction in the sky.
Each bright plate is exposed for about 45 minutes (similar to SDSS survey).
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|
Bulge |
Galactic component of high stellar density at the
center of the Milky Way.
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|
CAS |
Catalog Archive Server
-- provides access to the object catalogs and related
data from the Sloan Digital Sky Survey.
|
|---|
|
CWD |
Cool white dwarf -- white dwarf star with temperature below
about 5000K.
CWDs exhibit a unique spectral signature due to collisionally-induced
absorption.
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|
dwarf galaxy |
Small, low luminosity galaxy. SEGUE/SDSS has discovered
several new dwarf galaxies in orbit about the Milky Way
(see SEGUE publications).
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|
Faint Plate |
One of two plates centered on a particular direction in the sky.
Each faint plate is exposed for about 1.5 hours.
|
|---|
| globular cluster |
Gravitationally bound clusters of hundreds of thousands of stars,
found in orbit about the Milky Way. SEGUE is targeting several globular
clusters as part of its
special plate category.
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|---|
| Halo |
The Milky Way is embedded in an enormous
halo of dark matter, which
extends far beyond the visible portions of the Galaxy.
|
|---|
| l-color |
Principle component color:
l = -0.436u + 1.129g - 0.119r - 0.574i + 0.1984
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| line index |
Line index, or equivalent width, is a measure
of the intensity of an absorption line in the spectrum.
The SSPP measures 77 atomic and molecular lines, which
are used in estimating
stellar parameters.
Line indices are
calculated from SEGUE spectral data by integrating a continuum normalized
flux over the specified wavelength region of each line band.
A list of indices for DR7 SEGUE SSPP can be found on
|
|---|
| metallicity |
Metallicity is a measurement of the heavy element
(anything heavier than Helium)
abundance in a star. It is often expressed in the
relative abundance
of iron to hydrogen, normalized to the solar metallicity on a logarithmic
scale: [Fe/H].
Stars with solar metallicity have [Fe/H] = 0; a star with [Fe/H] = -1 has
one-tenth solar metallicity.
Details of SEGUE methods to determine metallicities can be found
in Lee et al.
2007a.
|
|---|
| open cluster |
A cluster of stars which is assumed to have formed from the same
giant molecular cloud. Open clusters are loosely bound gravitationally,
and are at approximately the same distance from us, with similar chemical
compositions. SEGUE has observed the open cluster
NGC 2420.
|
|---|
| P1(s) color |
Principle component color:
Color perpendicular to s-color (and thus perpendicular to the stellar locus).
P1(s) = P1 = 0.91(u-g) + 0.415(g-r) -1.280
|
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| photometric metallicity |
Estimation of metallicity from photometric data.
|
|---|
| photometric parallax |
Method for estimating the distance to stars based on
their colors and apparent luminosity.
|
|---|
| pipeline |
see SSPP
|
|---|
|
Principle Component Color Analysis |
Parametrization of stellar locus in color space,
which can be used
to separate stellar populations based on properties such as
metallicity, surface gravity or temperature.
See
Newberg & Yanny 1997 ApJS 113, 89;
Lenz, D., Newberg, H., Rosner, R.,
Richards, G. & Stoughton, C. 1998 ApJS 119, 121; and
Helmi, Ivezic et al 2003 ApJ 586, 195.
|
|---|
| Principle Component
classification of galaxies |
Automated method for objective
classification of large numbers of galaxies using spectral data.
See for example
Yip et al 2004
and referenences therein.
|
|---|
| proper motion |
Observed motion of an object on the sky; often given
in arcsec/year for stars. SEGUE compares the positions of objects with
their position in previous surveys such as USNO-B to derive
proper motions. See
Munn et al. 2004
|
|---|
| Pop I |
Traditional classification of stars: Pop I stars are relatively
young and metal-rich. The Sun is a member of this category.
|
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| Pop II |
Pop II stars are older, more metal-poor than Pop I.
Pop II include the oldest observed stars.
|
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| Pop III |
Pop III are metal-free or extremely low
metallicity stars proposed to represent the first stars in the Universe.
|
|---|
| radial velocity |
The observed motion of an object along the line-of-sight.
Radial velocities are inferred from a shift in the spectral features. See
SEGUE radial velocity determination or
Yee et al 2007a for
details.
|
|---|
| resolution |
A measure of how well details can be distinguished. SEGUE/SDSS
spectral resolution, λ/ δλ ≈ 1800.
|
|---|
| SSPP |
SEGUE Stellar Parameter Pipeline.
SSPP uses a
combination of techniques to extract reliable estimates of stellar
parameters from the SEGUE spectroscopic data.
|
|---|
| s-color |
Principle component color:
s-color is a linear combination of (u-g), (g-r) and (r-i)
that runs parallel to the
stellar locus.
s = -0.249u + 0.794g - 0.555r + 0.234
|
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| S/N |
Signal to noise ratio.
|
|---|
| Spheroid |
Sometimes referred to as the stellar halo, the spheroid is
composed mainly of older stars and
is one of the main components of the Galaxy.
The exact shape and density distribution of the spheroid is still not
known (see for example
Newberg & Yanny
2005) although in general the density falls off more steeply than
the dark matter halo.
|
|---|
| Stellar stream |
Several streams of stars have been identified within the halo
of the Galaxy. These streams correspond to disrupted satellites of the
Milky Way.
SEGUE has already been instrumental in mapping
the substructure within the Galactic halo; finding new streams and
identifying their progenitors. A better understanding of stellar
streams and tidal debris within the halo will lead to a more complete
picture of the shape of the halo and the merger history of the Galaxy.
See the SEGUE
publications page for several recent references.
|
|---|
| surface gravity |
Surface gravity = log g.The surface gravity of a star
is related to its absolute luminosity class. Stars with lower surface
gravity are, in general, larger (giant stars), whereas stars with higher
surface gravity are in general, small, more compact (dwarf) stars.
Estimates of
log g are calculated from stellar spectra via the
SSPP.
|
|---|
| Target Selection |
Objects in the SEGUE photometric database are selected for
spectral observation based on a specific
target selection algorithm.
|
|---|
| Target type |
Segue targets objects for spectral observation using the
following abbreviations:
|
|---|
|
| AGB |
Asymtotic Giant Branch candidate star
|
| BHB |
Blue Horizontal Branch candidate star
|
| CVR |
Cool White Dwarf candidate star
|
| FTO |
F turnoff candidate star
|
| GAL |
SDSS main survey or LRG GALAXY candidate
|
| GD |
G Dwarf candidate star
|
| HOT |
HOT standard star (main SDSS Survey, g-r < 0)
|
| KD |
K Dwarf candidate star
|
| KG |
K Giant candidate star
|
| LOW |
Low metallicity candidate star
|
| MD |
M Dwarf candidate star
|
| PHO |
Photometric Standard star (usually brighter F dwarf)
|
| QA |
Quality Assurance target (in SEGUE, duplicates another fiber)
|
| QSO |
SDSS main survey QSO candidate
|
| RED |
Reddening Standard star (usually fainter F dwarf)
|
| ROS |
may be F/G dwarf or MS/WD or low lat target
|
| SER |
Serendip. Manual (1. globular/open cluster 2. High Prop motion)
|
| STA |
Main SDSS survey STAR (not GAL or QSO or Standard)
|
| SKY |
Sky fiber, should have no object flux
|
| WD |
White Dwarf candidate
|
|
|---|
| Teff
|
Effective temperature: Teff is estimated
from the spectral data, and also from g - r colors
(see
Yee et al 2007a.) |
|---|
| Thick Disk |
One of the major stellar components of the Galaxy, the
thick disk (with a scale height on the order of 1 kpc) extends beyond the
thin disk but
lies well within the dark matter halo.
The thick disk contains roughly 10% of the mass of the thin disk,
and its stars are in general older and more metal-poor.
SEGUE
will greatly extend our understanding of the shape, kinematics, composition
and origin of the thick disk.
SEGUE will also target the thick disk/halo
boundary and substructure.
|
|---|
| Thin Disk |
The thin disk (scale height ~ 0.3 kpc)
contains the vast majority of the stars in the
Milky Way. SEGUE's low latitude observations will help to disentangle
the stars of the thin and thick disk. SEGUE will also study the warp
and flare of the outer portion of the Galactic disk.
|
|---|
| vGSR |
Velocity (in km/s) corrected to the
Galactic Standard of Rest, assuming a solar velocity of
16.6 km/s toward α(J2000.0) = 17h49m58.7,
δ(J2000.0) = +28o07'04" and a motion of the local standard
of rest of 220 km/s toward α(J2000.0) = 21h12m01.1,
δ(J2000.0) = +48o19'47" .
|
|---|
| velocity dispersion |
Veocity dispersion σ is a measure of the spread in
velocities of individual objects within a larger structure. σ is
often used
to refer to the velocity dispersion of an integrated galaxy spectrum,
which probes the gravitational potential of the galaxy. SEGUE
will also study the velocity dispersions of Galactic components and
substructures.
|
|---|
| w-color |
Principle component color:
w = -0.227g+0.792r-0.567i+0.040
|
|---|
| wavelength coverage |
SEGUE and SDSS spectroscopy covers the wavelength range from
3,800 Å - 9,200 Å.
|
|---|
