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gaia-dpci / GaiaXPy

Gaia BP/RP spectra package
BSD 3-Clause "New" or "Revised" License
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Weird photometry in the SDSS and PS bands #25

Closed esm1966 closed 2 years ago

esm1966 commented 2 years ago

Hello, We at the Spanish Virtual Observatory are working on the access from VOSA (http://svo2.cab.inta-csic.es/theory/vosa/) to Gaia synthetic photometry and we've noticed something wrong with the fluxes in the SDSS and PS bands.

Working with magnitudes, everything works nicely and the Gaia synthetic photometry link perfectly with photometry from other catalogues. However, if fluxes are used instead, the fluxes at SDSS and PS bands are up to 12 orders of magnitude fainter than they should be. On the contrary, UBVRI and HST fluxes are OK.

I've experienced this behaviour both using the Gaia archive at ESAC or the Vizier service. There are lots of objects with this problem. You can, for instance, try with source_id= 151462022346240

Thank you very much in advance for your help. Best regards, Enrique Solano.

fdeangeli commented 2 years ago

This is a documentation problem. The documentation reports that the units of fluxes are W m^-2 nm^-1, but in fact it depends on the system (AB or Vega) used for a particular set of bands. If the system is AB the units are W m^-2 Hz^-1. This is correctly stated in Gaia Collaboration, Montegriffo et al. 2022 (see in page 4 the text following equation 2), but the GaiaXPy documentation needs to be corrected. Thank you for pointing out this inconsistency.