• First, open the page https://vizier.cds.unistra.fr/vizier/sed/
• Then, enter an object name or a position (objects names are resolved by the Sesame service) and a radius.
  The radius is currently limited to a maximum of 30 arcsec
• After a few seconds, you should see the photometric points displayed as a function of wavelength.

The user interface is made of 3 different panels:

1. The panel denoted ① displays the photometric points as a function of wavelength, frequency or energy.
   Error bars are shown if the original catalogue included information on uncertainties.
   Points are colour-coded according to the catalogues they have been extracted from (points coming from the same catalogue share the same colour).
   You can zoom in simply by dragging a rectangle around the area of interest. Zoom out by double clicking on an empty region of the plot, or using the reset zoom button.
2. The panel ② shows a small sky map of the queried region, centered on the requested target.
   Dragging a rectangle around an area will zoom in. Zoom out by double clicking or using the reset zoom button.
3. The tabular view in the panel ③ shows the actual frequency and flux values with links to the original catalogue and measurements.

These three panels are linked: clicking on a data point in the main plot or in the sky map will highlight the corresponding point in the other plot and in the table. Conversely, clicking on a table row will highlight the corresponding point in the 2 other panels.

The photometric points can be exported (through SAMP) to VO tools like Topcat or Aladin using the dedicated button .
They can also be retrieved directly as a VOTable using the following URL pattern: https://vizier.cds.unistra.fr/viz-bin/sed?-c=Target&-c.rs=Radius-in-arcsec
Example: https://vizier.cds.unistra.fr/viz-bin/sed?-c=Vega&-c.rs=1.5 will return the VOTable with photometric points for a 1.5 arcsec region around Vega.

The VizieR photometry tool allows for easy visualization of photometry points extracted around a sky position from photometry-enabled catalogues in VizieR. Even when an object name is used as a target, what is returned is just a list of photometry point found within some search radius, and should not be mistaken for an actual energy distribution for the target object: there is no guarantee that all photometry points correspond to the target, especially for extended sources.

The search radius has to be specified by the user. It is currently limited to a maximum of 30 arcsec. It depends mostly on the precision or quality of the coordinates (SIMBAD and VizieR catalogs), the resolution of the images from which the sources were extracted, source extent, and source crowding.

Suggestions are: crowded field: 0.5 to 1.5 arcsec, 3 arcsec otherwise; uncertain coordinates: 5 to 30 arsec (risky!).

Some catalogue magnitudes are converted automatically into fluxes using photometric system descriptions in the METAfltr VizieR table.

There is no correction for reddening applied: unless magnitude values in the original catalogue are already corrected for extinction, values will correspond to the observed reddened flux.