Comments to the UCD RFC
Patricio F. Ortiz
pfo at star.le.ac.uk
Tue Sep 20 09:45:51 PDT 2005
Some comments about the official list of UCD words:
* file http://vizier.u-strasbg.fr/UCD/ucd1-ucd1p.txt has one typo in
It should be spect.line.eqWidth.
* The following deprecated terms still appear in the list:
phot.fluxDens still in the list
phot.fluxDens.sb still in the list
phys.massYield still in the list
* The definition of arith.ratio can be used with quantities with different
UCDs, eg, axis ratio: semi-major and semi-minor axes have different UCDs.
Although the new UCD phys.size;arith.ratio doesn't make it clear that we're
dealing with an axis ratio, we could be comparing planet sizes... worrisome
* em.line... drop molecular, so far only atomic lines are mentioned, unless
molecular lines are to be added to the list.
S | instr.pixel | Pixel
S | instr.plate | Photographic plate
could be better off as Q
* pos.resolution... despite that most astronomical resolution is angular,
there are other resolutions in distance, eg, solar and planetary
phenomenae, and quite possibly a resolution in the distance scale.
Simplifying too much could be dangerous in the long run. Furthermore, the
angular resolution seems to me a quantity more related to the instrument
than an intrinsic property of the object position in space.
* seems to me that instr.seeing should become part of the obs.atmos family...
* S | obs.field | Region covered by the observation
Does the explanation encompass field of view? The equivalences with UCD1
doesn't seem to show that.
* I agree with Pierre that the section on polarization has been oversimplified
* phys.gravity: gravity is more than surface gravity, as it could be
measured around any * objcted at any distance from the surphace, and the
ones doing gravitational waves experiments may find this too limiting.
* Are numbers permitted in atoms? This: phys.mass.light may look much
better as phys.mass2ligth or phys.massToLight, light is not a property of
* People still quote "major axis" and "minor axis"... how do we fit this
with phys.size.smajAxis and phys.size.sminAxis ?
* temperature: people modelling interiors might want a few more flavours of
* Q | pos.earth.altitude | Altitude, height above the Earth's surface
Do we really mean Earth's surface, as in an airborne apparatus or above sea
level (to quote how high an observatory is?)
* time.x.start, and time.x.end . exposure is fine, observation is fine,
what about a phenomenon? eg, a solar flare? What about start and end of a
phenomenon at different levels of intensity/importance?
* in the area of photometry and color indices, how would I assign a UCD,
and later on recognize without having to sort through a ton of meta-data
a color index formed with two HST filters? Or Gunn filters? Just to name
two of the commonly used systems today and left out of the list.
If it's felt that there are too many UCDs in the phot field, at least leave
the root of the different photometric systems to avoid sorting irrelevant
data when one is digging a registry for Cousins V-I!!
P.S. the comments above also appear in the wiki page
Patricio F. Ortiz pfo at star.le.ac.uk
Department of Physics & Astronomy Phone: +44 (0)116 252 2015
University of Leicester
Leicester, LE1 7RH, UK
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