This document describes the list of controlled terms used to build the
Unified Content Descriptors, Version 1+ (UCD1+).
The document describing the current proposal for a new set of UCD called UCD1+
can be found at the url: http://www.ivoa.net/Documents/PR/UCD/UCD-20040823.html.
Here we briefly recall the structure of the proposed UCD1+ and the origin of
the present lists.
Status of this document
This is an IVOA Working Draft for review by IVOA members and other
interested parties. It is a draft document and may be updated, replaced,
or obsoleted by other documents at any time. It is inappropriate to use
IVOA Working Drafts as reference materials or to cite them as other than
``work in progress''. A list of current IVOA Recommendations and other
technical documents can be found at http://www.ivoa.net/Documents/.
Acknowledgments
This document is based on the W3C documentation standards, but has been
adapted for the IVOA.
1 Definition of atoms and words
A UCD is a string which contains textual tokens called ``words'', separated
by semicolons(;). A word is composed of ``atoms'', separated by periods(.).
So the hierarchy is the following:
atoms --> words --> composed words
UCD1+ are either single words, or composed words.
UCDs should be "controlled" (through a process that is also indicated in the
PR referenced above). Control should be exercised at the level of words (ucd1+)
but also at the level of the vocabulary (atoms) used to form words.
A consistent list of atoms should be mantained, making sure that the same
atom means always the same thing, even if used in combination with different
other atoms.
1.1 Definition of atoms
Atoms were defined following these guidelines:
1. abbreviations are kept to a minimum, and only if the result is not
ambiguous (ra, dec are OK, but t is ambiguous: we use time and
temperature instead).
2. atoms are not hyphenated. The separation is
marked by a capital letter to help readability (position angle = posAng)
unless the composed word has a well known acronym (signal to noise ratio = snr)
or short form (standard deviation = stdev)
1.2 Definition of words
The list of UCD1+ words presented in this document was generated applying
the rules and recommendations of PR-UCD-20040823 to VizieR.
The original motivation was to transform UCD1 into an improved version,
trying to build a list of combinations of new words that could describe
all the existing UCD1 terms.
The procedure that was used was the following:
Step 1. Select a UCD1.
Step 2. Get summary information, e.g.:
UCD1 description
list of catalogues/tables using that UCD1
list of column names associated to UCD1
list of units used for those columns
Step 3. Assess the consistency of this summary information. If in doubt,
Step 4. Get detailed information on catalogues/tables/columns descriptions.
Step 5. Assign UCD1+.
If the consistency test at Steps 3 was positive, a new UCD1+ was defined, and
assigned to all columns described by old UCD1.
If detailed additional information was necessary (Step 4),
new UCD1+ were assigned to each column
and then the results were grouped into "n" new UCD1+s.
Eventually, all the columns in VizieR had a new UCD1+ assigned to them.
This is slightly different from saying:
``this column in this catalog is assigned this UCD1+''
because the result of a UCD1+ assignation procedure applied to all columns
could lead in some cases to more precise UCD1+ or to new ones.
2 The structure of the UCD1+ tree
All existing UCD1+ words are grouped into 12 main categories. These
categories are expressed by the first atom of the word, whose possible
values are:
arith (arithmetics)
We include in this section concepts involving or indicating some
mathematical operation performed on the primary ``concept'' or just
the presence of an arithmetic factor or operator.
em (electromagnetic spectrum)
This section describes the electromagnetic spectrum, either in a
monochromatic way or in predefined intervals. The complete list of
proposed bands (in seven classical regions of the e.m. spectrum: radio,
millimeter, infrared, optical, ultraviolet, x-ray and gamma-ray), can
be found in the document
Note-EMSpectrum-20040520
instr (instrument)
In this section we gather all the quantities related to astronomical
instrumentation, e.g. detectors (plates, CCDs, etc.), spectrographs,
telescopes (but also observatories or missions), etc.
meta (metadata)
This section includes all the information that is not coming directly
from a measure, and info that could not be included in other sections.
obs (observation)
In principle under this section should go all words describing an
observation (the name of the observer or PI, the observing conditions,
the name of the field). In practice, the section is very ``thin''
and could be deleted, if the sparse content could be housed elsewere.
phot (photometry)
All the words describing photometric measures are included in this section.
Basically we distinguish between a flux density (flux per unit frequency
interval), a flux density integrated over a given e.m. interval (flux
if expressed linearly, mag if expressed by a log), or a flux expressed in
counts/s (if the setup of the detector is photon counting observing mode).
We also include ``colors'', which are differences of magnitudes (i.e.
ratios of fluxes) measured in different e.m. bands.
In the present proposal we tried to simplify the PHOT section of old
UCD1, keeping only the most important (used, diffuse) colors.
phys (physics)
Atomic and molecular data (mainly used for spectroscopy) and basic
physical quantities (temperature, mass, gravity, luminosity, etc.)
pos (positional data)
All quantities related to the position of an object, in general on the sky.
Angular quantities, with the exception of projections from spherical to
rectangular systems.
Also angular measurements in general (the angular size of an object is
in this section, its linear size is in the phys section).
The WCS FITS keywords are placed here for the moment.
spect (spectral data)
For historical reasons, photometric data taken in narrow spectral bands
with instruments called spectrographs are classified as spectroscopic
data.
Don't miss up with ``em''. Bi-dimensionally speaking, em represents the x
axis, phot and spect the y axis.
src (source)
This is a rather generic section, mainly devoted to source classifications.
For no other than practical reasons, variability, orbital and velocity data
are also included in this section.
stat (statistics)
Statistical information on measurements.
time (time)
Quantities related to time (age, date, period, etc.)
A List of valid words
All words are preceded by a ``syntax'' code that can help in the process
of building composed UCD1+. The code "P" means that the word can only be
used as "primary" or first word, "S" stands for only secondary, code
"Q" means that the word can be used indifferently as first or secondary
word.
S arith Arithmetic quantities
S arith.diff Difference between two quantities described by the same UCD
P arith.factor Numerical factor
P arith.grad Gradient
P arith.rate Rate (per time unit)
S arith.ratio Ratio between two quantities described by the same UCD
S arith.zp Zero point
S em Electromagnetic spectrum
S em.IR Infrared part of the spectrum
S em.IR.15-30um Infrared between 15 and 30 micron
S em.IR.3-4um Infrared between 3 and 4 micron
S em.IR.30-60um Infrared between 30 and 60 micron
S em.IR.4-8um Infrared between 4 and 8 micron
S em.IR.60-100um Infrared between 60 and 100 micron
S em.IR.8-15um Infrared between 8 and 15 micron
S em.IR.H Infrared H band
S em.IR.J Infrared J band
S em.IR.K Infrared K band
S em.UV Ultraviolet part of the spectrum
S em.UV.10-50nm Ultraviolet between 10 and 50 nm
S em.UV.100-200nm Ultraviolet between 100 and 200 nm
S em.UV.200-300nm Ultraviolet between 200 and 300 nm
S em.UV.50-100nm Ultraviolet between 50 and 100 nm
S em.X-ray X-ray part of the spectrum
S em.X-ray.hard Hard X-ray
S em.X-ray.medium Medium X-ray
S em.X-ray.soft Soft X-ray
Q em.energy Energy value in the em frame
Q em.freq Frequency value in the em frame
S em.gamma Gamma rays part of the spectrum
S em.gamma.hard Hard gamma ray
S em.gamma.soft Soft gamma ray
S em.line Designation of major atomic and molecular lines
S em.line.21cm 21cm hydrogen line
S em.line.Brgamma Bracket gamma line
S em.line.Halpha H-alpha line
S em.line.Hbeta H-beta line
S em.line.Hgamma H-gamma line
S em.line.OIII [OIII] line
S em.mm Millimetric part of the spectrum
S em.mm.100-200GHz Millimetric between 100 and 200 GHz
S em.mm.1500-3000GHz Millimetric between 1500 and 3000 GHz
S em.mm.200-400GHz Millimetric between 200 and 400 GHz
S em.mm.30-50GHz Millimetric between 30 and 50 GHz
S em.mm.400-750GHz Millimetric between 400 and 750 GHz
S em.mm.50-100GHz Millimetric between 50 and 100 GHz
S em.mm.750-1500GHz Millimetric between 750 and 1500 GHz
S em.opt Optical part of the spectrum
S em.opt.B Optical B band between 400 and 500 nm
S em.opt.I Optical I band between 750 and 1000 nm
S em.opt.R Optical R band between 600 and 750 nm
S em.opt.U Optical U band between 300 and 400 nm
S em.opt.V Optical V band between 500 and 600 nm
S em.radio Radio part of the spectrum
S em.radio.100-200MHz Radio between 100 and 200 MHz
S em.radio.12-30GHz Radio between 12 and 30 GHz
S em.radio.1500-3000MHz Radio between 1500 and 3000 GHz
S em.radio.20-100MHz Radio between 20 and 100 MHz
S em.radio.200-400MHz Radio between 200 and 400 MHz
S em.radio.3-6GHz Radio between 3 and 6 GHz
S em.radio.400-750MHz Radio between 400 and 750 MHz
S em.radio.6-12GHz Radio between 6 and 12 GHz
S em.radio.750-1500MHz Radio between 750 and 1500 MHz
Q em.wavenumber Wavenumber value in the em frame
Q em.wl Wavelength value in the em frame
Q em.wl.central Central wavelength
Q em.wl.effective Effective wavelength
S instr Instrument
Q instr.ang-res Angular resolution
Q instr.antenna-temp Antenna temperature
Q instr.area Collecting area of detector
Q instr.background Instrumental background
Q instr.bandpass Bandpass of instrument
Q instr.bandwidth Bandwidth of the instrument
Q instr.baseline Baseline for interferometry
Q instr.beam-width Radio beam width
Q instr.calib Calibration parameter
S instr.det Detector
Q instr.det.noise Instrument noise
Q instr.det.psf Point Spread Function
Q instr.det.qe Quantum efficiency
S instr.filter Filter
Q instr.filter.transm Filter transmission
Q instr.fov Field of view
S instr.obsty Observatory satellite mission
Q instr.obsty.site Observatory location
Q instr.obsty.site.seeing Seeing
Q instr.offset Offset angle respect to main direction of observation
Q instr.param Various instrumental parameters
S instr.pixel Pixel
S instr.plate Photographic plate
Q instr.plate.emulsion Plate emulsion
Q instr.precision Instrument precision
Q instr.saturation Instrument saturation threshold
Q instr.scale Instrument scale (for CCD, plate, image)
Q instr.sensitivity Instrument sensitivity, detection threshold
Q instr.setup Instrument configuration or setup
Q instr.sky-level Sky level
Q instr.sky-temp Sky temperature
S instr.spect Spectrograph
Q instr.spect.dispersion Dispersion of spectrograph
Q instr.spect.order Spectral order
Q instr.spect.resolution Spectral resolution
S instr.tel Telescope
Q instr.tel.focus Telescope focus
S meta Metadata
P meta.bib Bibliographic reference
P meta.bib.author Author name
P meta.bib.bibcode Bibcode
P meta.bib.fig Figure in a paper
P meta.bib.journal Journal name
P meta.bib.page Page number
P meta.bib.volume Volume number
P meta.code Code or flag
P meta.code.class Classification code
P meta.code.member Membership code
P meta.code.mime MIME type
P meta.code.multip Multiplicity or binarity flag
P meta.code.qual Quality code
P meta.cryptic Unknown or impossible to understand quantity
S meta.dataset Dataset
Q meta.file File
S meta.fits FITS standard
Q meta.fits.software Software used in generating FITS file
P meta.id Identifier, name or designation
P meta.id.assoc Identifier of associated counterpart
P meta.id.cross Cross identification
P meta.id.parent Identification of parent source
S meta.main Main value of something
S meta.modelled Quantity was produced by a model
P meta.note Note or remark (longer than a code or flag)
P meta.number Number (of things; e.g. nb of object in an image)
P meta.record Record number
P meta.ref Reference, or origin
Q meta.ref.url URL, web address
Q meta.table Table or catalogue
Q meta.table.axis Table axis
P meta.title Title or explanation
P meta.ucd UCD
P meta.unit Unit
S obs Observation
S obs.air Atmosphere
Q obs.air.extinction Atmospheric extinction
Q obs.air.mass Airmass
Q obs.field Region covered by the observation
Q obs.image Image
Q obs.observer Observer, discoverer
Q obs.param Various observation or reduction parameter
S phot Photometry
Q phot.calib Photometric calibration
Q phot.color Color index or magnitude difference
Q phot.color.Cous Color index in Cousins system
Q phot.color.Gen Color index in Geneva system
Q phot.color.Gunn Color index in Gunn system
Q phot.color.JHN Color index in Johnson 65+ system
Q phot.color.STR Color index in Stroemgren system
Q phot.color.STR.c1 c1 Stroemgren color
Q phot.color.STR.b-y b-y Stroemgren color
Q phot.color.STR.m1 m1 Stroemgren
Q phot.color.excess color excess
Q phot.color.reddFree Dereddened color
Q phot.count Flux expressed in counts(/s)
Q phot.fluence fluence
Q phot.flux Photon flux
Q phot.flux.bol Bolometric flux
Q phot.fluxDens Flux density (per wl/freq/energy interval)
Q phot.fluxDens.sb Flux density surface brightness
Q phot.limbDark Limb-darkening coefficients
Q phot.mag Photometric magnitude
Q phot.mag.bc Bolometric correction
Q phot.mag.bol Bolometric magnitude
Q phot.mag.distMod Distance modulus
Q phot.mag.reddFree Dereddened magnitude
Q phot.mag.sb Surface brightness magnitude
Q phot.sb Surface brightness
S phys Physical quantities
Q phys.SFR Star formation rate
Q phys.absorption Extinction or absorption
Q phys.absorption.coeff Absorption coefficient
Q phys.absorption.gal Galactic extinction
Q phys.absorption.gf Gaunt factors
Q phys.absorption.opticalDepth Optical depth
Q phys.abund Abundance
Q phys.abund.Fe Fe/H abundance
Q phys.abund.X Hydrogen abundance
Q phys.abund.Y Helium abundance
Q phys.abund.Z Metallicity abundance
Q phys.acceleration Acceleration
Q phys.albedo Albedo or reflectance
Q phys.angMomentum Angular momentum
S phys.at Atomic physics
Q phys.at.branchingRatio Branching ratio
Q phys.at.collStrength Collisional strength
Q phys.at.crossSection Atomic cross-section
Q phys.at.einstein Einstein coefficient
Q phys.at.lande Lande factor
S phys.at.level Atomic level
Q phys.at.lineBroad Line broadening coefficient
Q phys.at.lineShift Line shifting coefficient
Q phys.at.moment Atomic momentum
Q phys.at.moment.electric Electric momentum
Q phys.at.moment.magnetic Magnetic momentum
Q phys.at.number Atomic number Z
Q phys.at.oscStrength Oscillator strength
Q phys.at.qn Atomic quantum number
Q phys.at.qn.I Nuclear spin quantum number
Q phys.at.qn.S Electronic spin quantum number
Q phys.at.qn.L Electronic L quantum number
Q phys.at.qn.J Coupling of S and L qn
Q phys.at.qn.F Coupling of J and I qn
Q phys.at.term Atomic term
Q phys.at.wOscStrength Weighted oscillator strength
S phys.atmol Atomic and molecular physics (shared properties)
S phys.atmol.coll Related to collisions
Q phys.atmol.configuration Configuration
S phys.atmol.element Element
S phys.atmol.ion Ion
S phys.atmol.ionization Related to ionization
Q phys.atmol.parity Parity
S phys.atmol.state.final Quantity refers to final state
S phys.atmol.state.initial Quantity refers to initial state
Q phys.atmol.sweight Statistical weight
S phys.atmol.trans Transition between states
Q phys.columnDensity Column density
Q phys.density Density (of mass, electron, energy...)
Q phys.dielectric Complex dielectric function
Q phys.dispMeas Dispersion measure
Q phys.distance Distance (not angular)
Q phys.distance.compon Component of distance vector
Q phys.distance.gc Galactocentric distance
Q phys.electField Electric field
S phys.electron Electron
Q phys.electron.degen Electron degeneracy parameter
Q phys.electron.energy Electron energy
Q phys.emissMeasure Emission measure
Q phys.emissivity Emissivity
Q phys.energy Energy
Q phys.eos Equation of state
Q phys.excitParam Excitation parameter U
Q phys.extension Angular extension, width, diameter
Q phys.gravity Surface gravity
Q phys.ionizParam Ionization parameter
Q phys.ionizParam.coll Collisional ionization
Q phys.ionizParam.rad Radiative ionization
Q phys.luminosity Luminosity
Q phys.luminosity.fun Luminosity function
Q phys.magAbs Absolute magnitude
Q phys.magAbs.bol Bolometric absolute magnitude
Q phys.magField Magnetic field
Q phys.mass Mass
Q phys.mass.fraction Mass fraction
Q phys.mass.light Mass to light ratio
Q phys.mass.loss Mass loss
Q phys.massYield Mass yield
Q phys.mol Molecular data
Q phys.mol.dipole Molecular dipole
Q phys.mol.dipole.magnetic Magnetic molecular dipole
Q phys.mol.dipole.electric Electric molecular dipole
Q phys.mol.formationHeat Formation heat for molecules
Q phys.mol.qn Molecular quantum numbers
Q phys.mol.quadrupole Molecular quadrupole
Q phys.mol.quadrupole.magnetic Magnetic molecular quadrupole
Q phys.mol.quadrupole.electric Electric molecular quadrupole
S phys.mol.rotation Molecular rotation
S phys.mol.vibration Molecular vibration
Q phys.polarization Polarization
Q phys.polarization.posAng Polarization angle
Q phys.polarization.rotMeas Rotation measure polarization
Q phys.polarization.stokes Stokes polarization
Q phys.pressure Pressure
Q phys.refraction Refraction
Q phys.size Size (not angular)
Q phys.size.area Area
Q phys.size.diameter Diameter
Q phys.size.radius Radius
Q phys.temperature Temperature
Q phys.temperature.effective Effective temperature
Q phys.temperature.electron Electron temperature
S pos Position and coordinates
Q pos.ang Angular distance
Q pos.ang.separation Angular separation
Q pos.az Position in alt-azimutal frame
Q pos.az.alt Alt-azimutal altitude
Q pos.az.ha Alt-azimutal hour-angle
Q pos.az.zd Alt-azimutal zenith distance
S pos.barycenter Barycenter
Q pos.det Position on instrument detector
Q pos.dirCos Direction cosine
S pos.earth Coordinates related to Earth
Q pos.earth.lat Latitude on Earth
Q pos.earth.lon Longitude on Earth
Q pos.earth.nutation Earth nutation
Q pos.ec Ecliptic coordinates
Q pos.ec.lat Ecliptic latitude
Q pos.ec.lon Ecliptic longitude
Q pos.ee Position ellipse error
Q pos.ephem Ephemeris
Q pos.eq Equatorial coordinates
Q pos.eq.dec Declination in equatorial coordinates
Q pos.eq.dec.arcsec Arcsec of declination
Q pos.eq.ra Right ascension in equatorial coordinates
Q pos.eq.ra.minutes Minutes of right ascension
Q pos.eq.ra.seconds Seconds of right ascension
Q pos.frame Reference frame used for positions
Q pos.gal Galactic coordinates
Q pos.gal.compon Cartesian component of galactic coordinates
Q pos.gal.lat Latitude in galactic coordinates
Q pos.gal.lon Longitude in galactic coordinates
Q pos.lunar Lunar coordinates
Q pos.lunar.occult Occultation by lunar limb
Q pos.parallax Parallax
Q pos.parallax.dyn Dynamical parallax
Q pos.parallax.phot Photometric parallaxes
Q pos.parallax.spect Spectroscopic parallax
Q pos.parallax.trig Trigonometric parallax
Q pos.pm Proper motion
Q pos.pm.dec Proper motion in declination
Q pos.pm.ra Proper motion in right ascension
Q pos.posAng Position angle
Q pos.precess Precession
Q pos.precess.dec Precession in declination
Q pos.precess.ra Precession in right ascension
Q pos.proj Projected coordinates
Q pos.sg Supergalactic coordinates
Q pos.sg.compon Cartesian component of supergalactic coordinates
Q pos.sg.lat Latitude in supergalactic coordinates
Q pos.sg.lon Longitude in supergalactic coordinates
S pos.wcs WCS keywords
P pos.wcs.cdmatrix WCS CDMATRIX
P pos.wcs.crpix WCS CRPIX
P pos.wcs.crval WCS CRVAL
P pos.wcs.ctype WCS CTYPE
P pos.wcs.naxes WCS NAXES
P pos.wcs.naxis WCS NAXIS
P pos.wcs.scale WCS scale or scale of an image
S spect Spectroscopy
Q spect.doppler Doppler parameter b
Q spect.index Spectral index
S spect.line Spectral line
Q spect.line.asymmetry Line asymmetry
Q spect.line.broad Spectral line broadening
Q spect.line.broad.Zeeman Zeeman broadening
Q spect.line.eqwidth Line equivalent width
Q spect.line.intensity Line intensity
Q spect.line.profile Line profile
Q spect.line.veloc Spectral line radial velocity
Q spect.line.width Spectral line fwhm
S src Source
Q src.class Source classification (star, galaxy, cluster...)
Q src.class.color Color classification
Q src.class.distance Abell distance class
Q src.class.luminosity Luminosity class
Q src.class.richness Richness Abell class
Q src.class.star-galaxy Star/galaxy discriminator
Q src.class.struct Bautz-Morgan structure classification
Q src.density Density of sources
Q src.ellipticity Source ellipticity
Q src.fwhm Source FWHM angular size
Q src.impactParam Impact parameter
Q src.morph Morphology structure
Q src.morph.param Morphological parameter
Q src.morph.scLength Scale length for a galactic component (disc or bulge)
Q src.morph.type Hubble morphological type (galaxies)
Q src.orbital Orbital parameters
Q src.orbital.eccentricity Orbit eccentricity
Q src.orbital.energy Orbital energy
Q src.orbital.inclination Orbit inclination
Q src.orbital.meanAnomaly Orbit mean anomaly
Q src.orbital.node Ascending node
Q src.orbital.periastron Periastron
Q src.orbital.separation Separation between orbital components
Q src.orbital.size Size of orbit major axis
Q src.orbital.veloc Orbital velocity
Q src.redshift Redshift
Q src.sample Sample
Q src.separation Separation between sources
Q src.spType Spectral type MK
Q src.var Variability of source
Q src.var.amplitude Amplitude of variation
Q src.var.index Variability index
Q src.var.pulse Pulse
Q src.veloc Radial velocity
Q src.veloc.ang Angular velocity
Q src.veloc.cmb CMB velocity
Q src.veloc.compon Component velocity
Q src.veloc.dispersion Velocity dispersion
Q src.veloc.escape Escape velocity
Q src.veloc.expansion Expansion velocity
Q src.veloc.gc Galactocentric radial velocity
Q src.veloc.geoc Geocentric radial velocity
Q src.veloc.hc Heliocentric radial velocity
Q src.veloc.lg Local Group radial velocity
Q src.veloc.lsr Local Standard of Rest radial velocity
Q src.veloc.microTurb Microturbulence velocity
Q src.veloc.pulsat Pulsational velocity
Q src.veloc.rotat Rotational velocity
S stat Statistical parameters
Q stat.Fourier Fourier coefficient
Q stat.Fourier.amplitude Amplitude Fourier coefficient
P stat.covariance Covariance between two parameters
P stat.error Statistical error
P stat.error.sys Systematic error
Q stat.fit Fit
Q stat.fit.chi2 Chi2
Q stat.fit.dof Degrees of freedom
Q stat.fit.goodness Goodness or significance of fit
Q stat.fit.omc Observed minus computed
Q stat.fit.param Parameter of fit
Q stat.fit.residual Residual fit
Q stat.likelihood Likelihood
S stat.max Maximum or upper limit
S stat.mean Mean, average value
S stat.median Median value
S stat.min Minimum or lowest limit
Q stat.param Parameter
P stat.snr Signal to noise ratio
P stat.stdev Standard deviation
Q stat.value Miscellaneous value
P stat.variance Variance
P stat.weight Statistical weight
Q time Time
Q time.age Age
Q time.crossing Crossing time
Q time.epoch Epoch, julian date
Q time.equinox Equinox
Q time.expo Exposure time
Q time.expo.end end exposure
Q time.expo.start start exposure
Q time.interval Interval
Q time.period Period
Q time.phase Phase
Q time.relax Relaxation time
Q time.resolution Time resolution
Q time.scale Timescale
B Changes from previous versions
Changes from v0.1
Descriptions of the words were improved.
Designation of commonly used lines have been moved to em.line.*. As a consequence,
terms like em.IR.K.Brgamma or spect.index.Hbeta have been removed.
phys.at and phys.mol have been completely reorganized to improve
the overall description of this domain. A new branch phys.atmol has been introduced
to group concepts shared between phys.at and phys.mol.
The phot.color section was significantly simplified.
Missing nodes of the tree were added (e.g. em.gamma, em.mm, pos.sg).
Creation of new words: em.wavenumber, meta.ucd, stat.error.sys
Typos were corrected in em.opt.* units and a few other descriptions.
