relative fluxes

[Rob Seaman]

On Jun 22, 2009, at 6:11 AM, Miguel Cerviño wrote:

> Yes, it needs solving: ALL theoretical spectra (stellar atmospheres,  
> and galaxy models with galaxy mass as free parameter) have the scale  
> problem

Does this only arise on the theory side?  The justification would be  
stronger for a general solution if there were also empirical use cases.

> If you work with color (also theoretical) you need the offset (zero  
> point) and the scalling factor (solar masses)

How should this be expressed?  For example:  units = 1.33 Msun + 0.43 ?

Is there a preferred representation such that an applications that  
doesn't need this feature can recognize scaled units (without a full  
parser) and throw an exception?

> Stellar atmosphere models can be described as an Intensity or as an  
> Eddington Flux.
> The dimensions in both cases are exactly the same, but there are a  
> 4Pi factor of difference between both quantities (an solid angle  
> integral). It can be solved with the Sebastien approach?

I think this is a different issue.  Some units might have an explicit  
per-steradian, for instance.  Or it might be implicit in the  
quantity.  It does raise the issue of whether the scaling factor  
itself can be an expression involving named values such as pi.

In general we should be concerned, perhaps, that all these interesting  
comments about units imply that there may be problem requirements that  
have yet to be discovered.  Also, is the VO really the first community  
to address these issues, or can we steal a solution from someone else?

Rob