[fitsbits] How to specify the "dex" unit? {External}

Ole Streicher ole at aip.de
Wed Oct 23 05:37:51 EDT 2024


Hi,

I want to have some metallicity values in a FITS table that are written 
with "dex" as unit. From the FITS standard (4.0) I learned that one 
could use the "log" function for that. However, as the "base" is 
dimensionless I am unsure how to write this. Is "log()" correct, i.e. is 
a dimensionless unit specified as an empty string? (I couldn't find that 
specified in the standard)

The VOUnits standard recently changed (in version 1.1) the 
representation of a dimensionless unit from the empty string to the 
string "1"; however "log(1)" is probably not FITS conform. Although I 
didn't see a restriction for units that "1" would not be a valid unit.

Can someone help me to clarify this?

Best

Ole



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