Addition of passband magnitude system field

[focanag]

ADES 2022a (and previous versions) allow reporting photometric information within the 'photometry group'. When the group is present, the keys 'mag' and 'band' are required. 'mag' is defined as the apparent magnitude in the specified band, and even though the passband is usually defined in a magnitude system, it may still be ambiguous. It will be more precise with a field to indicate the magnitude system used (it could be optional, with Vega as default). Most modern passbands systems are on the AB magnitude system, but there is still a wide use of Vega magnitudes (e.g., a query to Gaia DR3 returns G magnitude in Vega system). Even in the infrared some surveys may want to report directly in Janskys.

Now that you are considering some changes in the photometry group (adding multi-band photometry #2, maybe filter reporting #4…). Would you please consider the addition of the magnitude system and the use of flux units (Jy) instead of magnitudes?

Paco Ocaña (on behalf of the NEOCC team)

[stevechesley]

After a bit of research and discussion on this issue, I have understood that the combination of <band> and <photCat> unambiguously tell the user which magnitude system is used. Is there a need to be even more explicit (or redundant?), given the desire to avoid adding gratuitous ADES elements?

[focanag]

We propose to add the magnitude system field because we consider it is indeed ambiguous. One would suppose magnitudes referred to Gaia catalogue are in Vega system (certainly Gaia catalogue queries return G magnitude in Vegamags), however there is nothing against using AB magnitudes while using Gaia catalogue, as they provide ZPs for both systems (indeed it is actually done, see for instance https://www.wis-tns.org/object/2017jt/discovery-cert ).

Moreover, we think this is even probable for observatories using a lighter local version of Gaia catalogue, and for whatever reason favouring AB magnitudes in their processing pipelines. The difference could be significant in the NIR. For longer wavelengths we propose the possibility of reporting fluxes in Jy.

[stevechesley]

I believe that the photometric catalog should unambiguously define the magnitude system; that is part of the reason for specifying the catalog. In the case of Gaia, where the baseline system is Vega, but AB system photometry is also available, a different catalog ID should be defined by the MPC for AB mags. If the photometric catalog ID unambiguously defines the magnitude system, then further description seems redundant. I will discuss with the MPC to see what their perspective is.

Please explain better the rationale for reporting flux in Jy, rather than mags...

[focanag]

We find OK the solution to have the magnitude system unambiguously included in the definition of the catalog and therefore assigned a unique catalog ID.

Regarding the report of fluxes, we consider that beyond the visible domain (NEO Surveyor, NEOMIR…) the scientific common practice is to use the measured fluxes in Jy. The use of magnitudes implies the assumption of physical properties that may be not known at the moment of the reporting.

[stevechesley]

Per discussion with @federicaspoto this should be resolved by clarifying and extending the list of catalogs maintained by the MPC. For example,

*Cat      Description
Gaia3     Gaia DR 3 (Vega)
Gaia3_AB  Gaia DR 3 (AB)

Or something like that...