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PS1 took approximately 370,000 exposures |
from 2010 to 2015, each exposure consisting of 60 CCD images. These |
exposures are detrended, astrometrically calibrated, resampled (warped) onto a standard sky coordinate grid, stacked, and differenced. The different types of images are described below. More details about image filenames and data formats are included in the description of the PS1 Image Cutout Service. |
The following information is taken from Waters et al. and Magnier et al., which should be cited appropriately.
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Planned content:
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Schematic of the images and analysis processing stage of the PS1 IPP Pipeline, described in Magnier et al. |
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Raw images
Raw ImagesAfter an exposure is taken at the summittelescope, the raw image files of the 60 OTA CCDs (see PS1 GPC1 camera) are corrected for persistence issues and then handed over to the the PS1 IPP processing pipeline for further analysis. The STScI PS1 public archive Archive does not provide these images.
Camera
Imagesimages
The camera images are created by by applying PS1 Exposure detrending to the raw images (i.e.g., masking, bias subtraction, flat fielding), and applying an determining the astrometric and photometric calibration. The STScI PS1 public archive Archive does not provide these images.
Warps
Warps are the result of resampling and realigning the camera images onto regular areas (called skycells) on the sky (basically aligned N-S, E-W). How this is done depends on the particular tessellation. Different surveys may have different tessellations. A warp will generally consist of several different OTAs, therefore there are gaps between the OTAs, as well as the smaller gaps between the cells. Warps are astrometrically and photometrically calibrated. These images can be accessed and downloaded through the PS1 archive.
Stacks
Stacks are the 'optimal' combination of multiple warps on the same skycell. For the 3pi this may only be 10 or so warps, but for the Medium Deeps it can be several hundred. Stacks are also astrometrically and photometrically calibrated. These images can be accessed and downloaded through the PS1 archive.
Image artifacts and anomalies
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Warp images (available in DR2)
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Stack images (DR1)
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Difference images (planned to be available in future)
Difference ImagesDifference images are created by subtracting a warp from another image, in general the stack, after matching the PSFs and normalization using a spatially varying kernel. All static objects like such as galaxies and constant stars are subtracted out, and only the excess flux from the different epochs is left. Even though the differences images are not stored on disk, they can be created, and it is planned to make them accessible through the STScI PS1 at interface in a later release.
Mask Image
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Mask Images
All images, warps and stacks, have Pixel Flags set for each individual pixels.
Weight Images
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Weight Image
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