Page History

...

where the zeropt is 25 for the stacks.

Why do some catalog objects apparently not have images available?

The PS1 catalog includes some sources south of the nominal -30° declination limit of the PS1 3PI survey.  If the positions of those sources are entered in the PS1 Image Cutout Service, it reports that there is no data available because they are south of the declination limit.  This naturally leads to the question of why an object in the catalog does not have an associated image.

The PS1 project did take a small amount of data south of -30 degrees declination.  We are not sure about the history of these fields – they could have been either accidents or experiments.  When there were exposures available, the catalog pipeline software did process the images and extracted sources from them.

However, the image processing software did not produce any stacked images (combining the exposures) for these southern fields.  The data only got processed to the single-exposure level, so there presumably are no stack detections or other data products derived from the stack images.  There are some individual exposure images in these regions, but those will not be available for download until the DR2 data release (which we are hoping will be completed in 2018.) 

That is why there can be sources in the catalog that do not have associated stack images available.  These sources should only occur in the far southern sky.