VOUnit for solar density or metallicity?

[Sebastien Derriere]

Le 24/05/2022 à 21:23, Tom Donaldson a écrit :
>   Hello VOUnits enthusiasts,
>
> I was doing some validation on the units in our TESS Input Catalog (TIC) SCS and TAP results and came across one I didn’t see how to fix.  We have apparently been using unit=”Sun” on two different types of columns, one meaning solar metallicity and one meaning solar density.  Although "Sun" is mentioned in the VOUnits standard, I couldn't understand what was meant, and "Sun" is not on the list of known units (Table 2).
>
> It's a little tempting to extrapolate from the known units "solLum", "solMass" and "solRad" and come up with something like "solDen" or even "solFEH", but those are obviously not on the known list either.
>
> Does anyone have thoughts on whether there are official ways to represent these units, or if not, unofficial but preferable alternatives?

Hi Tom,

*Sun* is a valid vounit symbol. It is described in the current 
Recommendation, and this
should not change in version 1.1 currently in preparation. The problem 
comes from the
validator that ignored Sun, but this should get fixed, see :
https://heptapod.host/nxg/unity/-/issues/11

The description of "Sun" says : relative to the Sun, e.g. abundances.
In most cases, it is indeed used for abundances, often with log(Sun) is 
the quantity is the
metallicity relative to the Sun expressed in log scale.
But your usage looks perfectly legit for density too, we have some 
columns in VizieR
where Sun is used as unit for "Stellar density in solar units".

One could argue that this is not a real unit, but a mere description of 
how some dimensionless
number was obtained. True, but it's a simple way to carry information, 
and does no harm.

So in short : don't change your table metadata, the validators should 
allow "Sun" (soon).
And please don't invent "solDen" or "solFEH" :)

Sébastien

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    (((    Sebastien Derrieresebastien.derriere at astro.unistra.fr
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