Hi all,
I was looking at some random spectra in AVspec to understand the quality of the spectra in the regions of Hydrogen lines. While looking at the headers I noticed some keywords that carry duplicated information or information that is not described.
Specifically, I noticed that RA2000 and DEC2000 are inserted by AAVSO and looking at their values I guess (after checking in Vizier) that they are in ICRS and coming mostly from GAIA EDR3.
However, in some files there are keyword, in guess added by the software used for data reduction like RA,DEC,EQUINOX and RSDECSYS, because they all share the same software version BASS Project 1.9.9.
To me having duplicated keywords like RA,DEC could cause confusion to a final user that is not aware of the full process of data reduction and validation of the spectra.
The first question that could arise is which one i need to use ? then why there are 2 coordinates for the same object?
Also I would like to point out that having EQUINOX and RSDECSYS (I guess is a typo for RADECSYS, that in FITS standard becomes RADESYS) could cause confusion because one could think that RA2000 and DEC2000 are FK5 instead of ICRS coordinates.
I know that the difference is in general small between FK5 and ICRS coordinates, but for bright nearby stars the ICRS coordinates at Gaia epoch due to the proper motions are not the same as in FK5.
If I may, I would like to suggest that during the validation process the non AAVSO standard spectroscopic keywords will be renamed using an HIERARCH keyword like:
HIERARCH AAVSO FLAG KEYWORD = value / comment
where FLAG is a short string that could help to identify the data provider keywords
and KEYWORD is the name of the original keyword.
Additionally, I suggest a keyword
RADESYS = ICRS
to clearly clarify the system used by RA2000, DEC2000.
Finally, RA2000 and DEC2000 have a label that is misleading. For what I see the values comes from Gaia EDR3 that has an epoch of 2016. Hence the label seems to point that the proper motions are applied to epoch 2000, instead the values are exactly the ones at epoch 2016.
So, I suggest renaming these keywords to RA, DEC and add a keyword that could help to reconstruct the provenance of the coordinates (GAIA EDR3 or another value).
best regards
Mauro