Add method for VizieR SED/Photometry viewer

[bsipocz]

Vizier has a very nice service called sed, where it returns the photometry for a given coordinate. It not exactly clear what catalogues it contain by default, but the goal here as usual, to get the same table the webform returns.

http://vizier.u-strasbg.fr/vizier/sed/

[krislars]

+1 Another nice thing about this service is that VizieR converts the magnitudes into fluxes with its own internal zero points, something that astropy.units does not do (see note here). So adding this service would be a nice way to add in Vegamag-to-flux capability.

[Mixpap]

You cannot just convert from mag to Flux, because this conversion depends on the telescope. But you can check how Vizier does this by using their METAfltr table (http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=METAfltr&-out.form=H) For example if you want to transform the WISE data from Vizier to Jy (http://vizier.u-strasbg.fr/viz-bin/VizieR?-6N&-plus=-+&-source=METAphot,METAfltr&-out.form=H&catid=0&photid=713) you find the conversion factor F0 for the specific wide bands and then you use the conversion F (Jy) = F0 10^(-0.4mag)

[tboch]

Vizier has a very nice service called sed, where it returns the photometry for a given coordinate. It not exactly clear what catalogues it contain by default, but the goal here as usual, to get the same table the webform returns.

VizieR tables taken into account are the ones for which there are fluxes or magnitudes properly described (ie that can be converted to fluxes).

This is an addition CDS would be happy to provide - cc @bmatthieu3 We'll send a PR when we have something available.