Page History
...
What are the brightest and faintest stars for which the data are reliable?
How reliable is PS1 photometry of nearby, bright galaxies?
There are two main problems you should be aware of which affect bright galaxies:
(1) oversubtraction of the sky background - this affects most Messier galaxies and some (most?
...
...
) of the larger NGC objects. As the background is subtracted independently from each filter, this can induce colour changes across the galaxy. In principle the polynomial used to store the background is stored and can be de-applied. However, as the subtraction is done at the warp stage, if you want stacked data the stacking procedure would have to be re-run. This facility is not available in DR1.
 | Messier 31 from the 3pi stacks showing an extreme example of the over-subtraction of the background. |
|---|
(2) issues with the row-by-row bias and continuity corrections - these are applied and therefore seen on individual ccd scales (~600 pixels). As this is done at the detrending stage this is currently very difficult to correct. There is an aspiration to re-analyse all bright galaxies but this has not yet been done.
 | Messier 106 - this is an extreme stretch of the r-band stack showing problems on the scale of individual ccds. |
|---|
