There are a lot of Gaia DR3 variables with the remark “Period adopted is from vari_short_timescale table as there is no period in the Special Object Study table.”, for example Gaia DR3 1921804591431954176.
Is it true that this information is an estimate and that own measurements using CCD photometry would be helpful because they provide a better value based on the light curve?
I would also like to ask this more generally, for other cases than Gaia DR3 1921804591431954176: Which sources of period information are so inaccurate that it is better to use your own measurements using CCD photometry?
most of these periods are spurious, the number of Gaia observations is usually not large enough to get a reliable period, and we have seen such short periods in red dwarfs, where they are highly unlikely.
So new observations are useful.
Regarding getting new observations to improve periods, if you asked me, I would reply that the cases when new photometry is more valuable is when the amplitudes are small and thus survey data like ZTF or ASAS-SN are not really useful to reliable detect variations (e.g. 0.01-0.05 mag.) or when stars are too bright for those surveys (e.g. brihter than 10 for ASAS-SN or 12.5 for ZTF).
The above is specially true when there are no TESS observations.
But all data are welcomed.
Gaia results in general are not good because of the observing cadence I mentioned above, and also classifications are not reliable because they only provided rough or multiple types.
Before submitting data on any star, especially low amplitude objects, it is important to check that the data being collected is precise enough to show consistent variations, that is, getting to know your setup and its performance.
I recently did a quick check for some Gaia DR3 variables of unknown type (VAR) with very short periods (<~0.025 d). I would say that the majority of such periods are wrong and need to be redefined (for relatively bright stars, it is possible in many cases with TESS data). I agree with @Sebastian_Otero regarding the cadence: this is the main source of the period uncertainty.
By the way, misclassifications are quite common for Gaia DR3 variable stars. Gaia frequently classifies other types of variable stars as RS Canum Venaticorum types, while for many YSOs, they are classified as LPVs.
I ran some scripts recently to try and identify these misclassifications.
The results show that, as of today (2025.6.3), there are at least 185 misclassified YSOs in the VSX that were classified by Gaia as L-type variables.
However, putting that aside, Gaia’s classification of ECL appears comparatively more accurate, although the periods might be incorrect. Is it possible to use Gaia’s ECL classification to improve the classification of unclassified variable stars in the VSX in bulk? @Sebastian_Otero
For example, stars from the GDS or the 3P1-PS1 catalog – variables in the former are often assigned the generic ‘VAR’ type, while the latter contains many misclassified eclipsing binaries.
Additionally, there are QSO/AGN catalogs from SDSS or LAMOST.
These could be used to improve the classification of ZTF entries in the VSX. Since they have spectroscopic confirmation, this improvement would be more accurate.
For instance, ZTF J122935.25+145103.3 is actually an AGN, but the VSX classifies it as an SR variable (I plan to submit a revision for this object soon).