Dear Roy,
On Wed, 24 Nov 2004, Roy Williams wrote:
> >>I find Section 3.4 confusing...does anyone else? phot.color is a
difference
> >>of two magnitudes, but does NOT have the associated word arith.diff.
>
> In this case there is a special semantic concept for the difference of
magnit$
> is called color. It would be equally correct to say "arith.diff;
phot.magnitu$
> is more efficient to use one word than two.
Yes, this is exactly the reason for using phot.color
> >> A temperature ratio is not a temperature, so
phys.temperature;arith.ratio $
> >> backwards to me.
>
> I agree. This should be "arith.ratio: phys.temperature"
arith.ratio also means "normalized", and a normalized temperature to me
is closer to the concept of "temperature" than to an anodin "ratio".
By the way, also "temperature in units of .... " is expressed by the two
words "arith.ratio" and "phys.temperature".
In this respect I dare say that absolute, non-relative values do not exist
in our context
(please, don't open a debate on this particular case!!)
>> >> If phot.color;em.opt.B;em.opt.V means B-V and
phot.color;em.opt.V;em.opt.B
> >>means V-B, then order is clearly important. The concern this all
raises for
> >>me is that the construction rules for new UCDs are not very clear, and
that
> >>the existing UCD1+s have a certain (large) amount of arbitrariness.
>
> Yes that is true. But not because of the UCD construction, rather
because of
> "color". Perhaps I can ask those mor knowledgeable than myself how
exactly color is
> defined? If I say "BV color" or "VB color", do they have opposite sign?
Or do$
> subtract the highest wavelength magnitude from the lowest wavelength?
>
B-V color means (Bmag - Vmag), so B-V = -(V-B)
so there is no arbitrariness in the order of em-bands when colors are
concerned.
Any way, we are testing an "ucd1+ builder" that will help
in building correct ucds from a list of words.
Example:
>From a description like: "Optical V magnitude" you can get from an
assignation tool the words: em.opt, em.opt.V, phot.mag .
The buider will propose: phot.mag;em.opt.V
>From a description like: "Optical to infrared color" the builder will
propose: phot.color;em.opt;em.IR
To Bob:
The reason for "Q" quantities is twofold:
1. Q is between P and S in the alphabet, as in ucd1+s
2. Q stands for "quantity", while P/S-words are usually not quantities
Andrea
Andrea Preite Martinez andrea-at-rm.iasf.cnr.it Istituto di Astrofisica Spaziale Tel.:+39.06.4993.4641 Area di Ricerca di Tor Vergata Fax.:+39.06.2066.0188 Via del Fosso del Cavaliere 100 Cell: 339.3817355 00133 Roma CDS: +33.3.90242448 ==============================================================================Received on 2004-11-24Z18:00:55