The OTA CCDs have known artifacts and anomalies. A lot of work has gone into characterizing these artifacts, and removing them if possible. Pixels affected by these artifacts or anomalies are kept tracked of in the mask images with pixel flags.
Certain CCDs suffer from an issue whereby the bias level varies between rows. A software fix based on a linear fit to the bias in each row (check if this is correct?) has been applied on CCDs prone to this effect, however
Example of problems on a warp caused around a bright galaxy by the row-by-row bias correction.
An example of uncorrected row-by-row bias effects imprinting through onto a stack.
The sky subtraction routine is known to over-subtract around large galaxies or areas of nebulosity. There is currently no fix for this.
On some stacks, if one or more input warps has poor astrometry this can imprint through to the stack (in particular, supposedly masked areas such as the centres of bright stars can show a background star field poking through). This is quite rare and mostly seen in crowded fields.
Put one or more images or figures at the top of this column. Novices may simply "Insert" an "Image" here. Experts should create first go to the "Media Repository" page and "Create" a new "PS1 image information" page for the new image. The image information page provide a mechanism for capturing metadata and including alternate versions of the figure.
Include an infobox below the picture. Summarize key facts in the infobox. The infobox helps users quickly assess the content of the article.