Bugfix: Download UCD1+ instead of UCD1 in Vizier client

[Kraysent]

Hi!

Problem

Found a bug: when trying to download a table from Vizier using get_catalogs_async method (and get_catalogs as a consequence) the resulting table only contains UCD1 identifier instead of UCD1+. This is a bug and not a backwards compatibility feature because the comment in the code explicitly states that it wants to download newer version: https://github.com/astropy/astroquery/blob/main/astroquery/vizier/core.py#L691

This results in a VOTable that only has older UCD1 syntax:

   <FIELD ID="RAJ2000" arraysize="13" datatype="char" name="RAJ2000" ucd="POS_EQ_RA_MAIN" xtype="hms">
    <DESCRIPTION>
     Right ascension in ICRS, at "Epoch" (1)
    </DESCRIPTION>
   </FIELD>

Instead of a UCD1+ one might expect:

   <FIELD ID="RAJ2000" arraysize="13" datatype="char" name="RAJ2000" ucd="pos.eq.ra;meta.main" xtype="hms">
    <DESCRIPTION>
     Right ascension in ICRS, at "Epoch" (1)
    </DESCRIPTION>
   </FIELD>

Code to reproduce:

from astroquery import vizier
catalogs = vizier.Vizier().get_catalogs("I/273A/erlcat")
tbl = catalogs[0]
tbl.write("test.vot", format="votable")

Solution

As UCD1+ is a newer syntax, I propose we just use it. To do that, as per Vizier spec, we only need to remove the U identifier from -out.meta parameter that requests the data, see the diff in this PR.

Potential compromises

This technically breaks backwards compatibility. As an alternative, we may pass some parameter to VizierClass instance that will query either new or old UCD syntax and which will default to old syntax. Not sure if this is necessary, though, as UCD1 was superseded by UCD1+ in 2005: https://www.ivoa.net/documents/REC/UCD/UCD-20050812.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.72%. Comparing base (91fad25) to head (7a4138d).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3458   +/-   ##
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  Coverage   70.72%   70.72%           
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  Files         232      232           
  Lines       20041    20041           
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  Hits        14174    14174           
  Misses       5867     5867           

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[bsipocz]

Cc @ManonMarchand

[ManonMarchand]

Hello,

Thanks for looking into this!

You're right, the default should be UCD1+ (and it's what is in the database anyhow so we avoid a conversion).
I think this deserves a changelog entry in the breaking change section though.