relative fluxes

Derriere Sebastien derriere at newb6.u-strasbg.fr
Mon Jun 22 04:46:03 PDT 2009

```> RELATIVE and NORMALIZED fluxes are dimensionless quantities: they are
> an ABSOLUTE flux divided by some reference flux value. Therefore the
> unit should be and empty string.

Hi all,

My first reaction was the same as Arnold's: relative fluxes (ratio of
the flux to some reference flux value) are dimensionless. But then how do you
describe what reference value has been used for the scaling? Add an extra
parameter, with its own UCD, unit, utype, etc...?

Then it hit me: that's the same as expressing a mass in Solar masses!
When you have a value of "1.44 solMass", you can interpret it as being
a dimensionless quantity: "1.44 numbers of solar masses", because it is the
ratio of the mass of the object to the mass of the sun.
You can also describe it as:
value="1.44"	unit="solMass" (and if you write 1.0 solMass...)
or describe it as:
value="1.44"	unit="2.0e30kg"

So thinking of a spectra normalized to a reference, value, the unit
could be this reference value! With Alberto's example:
value=[anything from 0.0 to 0.06]
unit="1.23e-4 erg/cm**2/s/Angstrom"  (or whatever the reference value)

My 2cents

Sebastien.

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