Date: Fri, 29 Mar 2024 03:28:17 -0400 (EDT) Message-ID: <1711798681.2370.1711697297434@ploutercf.stsci.edu> Subject: Exported From Confluence MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_Part_2369_1996320058.1711697297431" ------=_Part_2369_1996320058.1711697297431 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Location: file:///C:/exported.html
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, stacke=
d, and differenced. The different types of images are described below. More=
details about image filenames and data formats are included in the descrip=
tion of the PS1 Ima=
ge Cutout Service.
The following information is taken from Waters et al.= and Magnier et al., which= should be cited appropriately.
On this page
Schematic of the images and analysis processing = stage of the PS1 IPP Pipeli= ne, described in Magnier et al. |
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After an exposure is taken at the telescope, the raw image files of the = 60 CCDs (see PS1 GPC1 camera= ) are corrected for persistence issues and then handed over to the = ;PS1 IPP pipeline for f= urther analysis. The STScI PS1 Archive does not provide these images= .
The camera images are created by applying PS1 Exposure detrending to the raw i= mages (i.e., masking, bias subtraction, flat fielding), and determining the= astrometric and photometric calibration. The STScI PS1 Archive does not= provide these images.
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 tracked in the mask imag= es with = pixel flags. For more info see the PS1 Image artifacts and anomalies pag= e.
Warps are the result of resampling and realigning the camera images
The PS1 stack images, described in detail in Waters et al., are the 'optimal' combination of multiple warps on the same skycell. For= the 3pi survey there are in general 12 warps per filter, but for the Mediu= m Deeps it can be several hundred. Stacks are also astrometrically and phot= ometrically calibrated. These images are part of DR1 and can be accessed an= d downloaded through the PS1 archive image cutout interface. For more info see the PS1 Stack images page.
Difference images are created by subtracting a warp from another image, = in general the stack, after matching the PSFs and normalization using a spa= tially varying kernel. All static objects such as galaxies and constant sta= rs are subtracted out, and only the excess flux from the different epochs i= s 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 PS= 1 interface in a later release.
All images, warps and stacks, have Pixel Flags set= for each individual pixels. This information is saved in a mask image, whi= ch in general has the suffix .mask.fits(.fz) and mk.fits(.fz) for warp and = stack images, respectively. For more info see the PS1 Mask image page.
Weight images are variance maps. For single epoch PS1 Warp images, these variance contains the r= eadnoise, Poisson noise, and other noise sources. For PS1 Stack images, the noise is= propagated from the individual input warps. These weight images can be use= d for estimates of the uncertainties in the photometry. We note that the de= projection of the chip images into the warps correlates the pixels, introdu= cing covariance. Therefore the derived uncertainties might underestimate th= e true noise. For more info see the PS1 Weight image page.
PS1 3-color image of NGC 894