The PS1 data processing pipeline generates catalogs of discrete sources detected in the images. Each source may have measurements from one or more filters, and each filter may have measurements at one or more epochs. In the PS1 nomenclature, Detections are sources found in a single exposure, while Objects are either collections of Detections matched across exposures, or sources found in stacked images that combine multiple epochs to produce deeper detection limits. Only Objects are included in DR1; Detections will be included in DR2. All source information (positions, magnitudes, morphological information, flags, etc.) is stored in the PS1 databases, which will be the starting point for most science using PS1 data.
PS1 data processing generated a sequence of tables describing the catalogs. Catalogs include Detections and Objects. Detections are found in individual exposures, while Objects are either collections of Detections found at compatible locations in multiple images, or sources found in in stacked images (PS1: Stack objects and photometry). Only Objects are included in DR1; Detections will be released in DR2. For each source, many different properties are measured via several different procedures; the information is organized into Tables, described in detail below. Useful photometric measurements include: Aperture Photometry, PSF photometry, Kron photometry (especially relevant for non-opoint-sources), and Forced photometry. For sufficiently bright extended sources, the light distribution if fitted with de Vaucouleurs and Sersic models, with the paratmeters reported in the linked tables. In the descriptions below, the table names are linked to pages that give full descriptions of the columns. Pages are also available that give descriptions of both tables describing the objects (including the ones below) and tables with higher-level metadata such as information on flag values and filters.
ObjectThin: This is the master table for everything identified as an object in the 3pi survey (on both single and stacked exposures). An object associates single epoch detections and the stacked detections within a one arcsecond radius. The mean position from the single epoch data is used as the basis for coordinates when available, or the position of an object in the stack when it is not. The right ascension and declination for both the stack and single epoch mean is provided (weighted mean over all filters). The number of detections in each filter from single epoch data is listed, along with which filters the object has a stack detection. This table does not contain any photometric data and will usually be used in JOINs to other tables.
MeanObject: Contains the mean photometric information for objects based on the single epoch data, calculated as described in Magnier et al (2013). To be included in this table, an object must be bright enough to have been detected at least once in an individual exposure. PSFMag, KronMag, and APMag (plus statistics) are listed for all filters. The information for all filters for a given object are joined into a single row. This table is designed to be JOINed to ObjectThin, as it contains no positional information.
Detection: Contains single epoch photometry of individual detections from a single exposure in a single filter. The identifiers connecting the detection back to the original image and to the object association are provided. PSFFlux, APFlux, and KronFlux fluxes are included, and basic shape parameters (moments, FWHM) along with sky and detector coordinate positions and observation date/time. Note: The Detection table is not part of the DR1 data release; it will be included in the DR2 release.
StackObjectThin: Contains the positional and photometric information for all photometry of detections on the stacks. RA, Dec, PSFMag, APMag and KronMag are reported for each filter. The information for all filters are joined into a single row, with metadata indicating if this stack object represents the primary detection. Due to overlaps in the stack tessellations, an object may appear in multiple stack images, and so have several independent entries in this table. The primary detection is the unique detection from the stack image that provides the best coverage with minimal projection stretching. All other detections of the object in that filter are secondary, regardless of their properties. The detection flagged as best is the primary detection if that detection has a psfQf value greater than 0.98; if that is not met, then any of the primary or secondary detections with the highest psfQf value is flagged as best. This table can be used on its own as a primary source of stack photometry, although if you want mean positions you will need to JOIN to ObjectThin.
StackObjectAtrributes: For all stack detections it contains the PSFFlux, KronFlux, and APFlux fluxes (as opposed to magnitudes) for all filters in a single row, along with point-source object shape parameters (e.g. FWHM, moments). Also sky statistics, exposure times, basic s/g separation parameter. Needs to be JOINed to StackObjectThin to get positions.
StackApFlx: Contains the unconvolved fluxes within the SDSS R5 (r = 3.00 arcsec), R6 (r = 4.63 arcsec), and R7 (r = 7.43 arcsec) circular apertures (Stoughton 2003). Convolved fluxes within these same apertures are also provided for images convolved to 6 sky pixels (1.5 arcsec) and 8 sky pixels (2.0 arcsec). All filters are matched into a single row, one row per stack detection. Needs to be JOINed to StackObjectThin to get positions.
StackApFlxExGalUnc: Contains the unconvolved fluxes within the SDSS R3 (r = 1.03 arcsec), R4 (r = 1.76 arcsec), R5 (r = 3.00 arcsec), R6 (r = 4.63 arcsec), R7 (r = 7.43 arcsec), R8 (r = 11.42 arcsec), R9 (r = 18.20 arcsec), R10 (r = 28.20 arcsec), and R11 (r = 44.21 arcsec) circular apertures for stack detections. All filters are matched into a single row. These measurements are only provided for objects in the extragalactic sky, i.e., they are not provided for objects near the Galactic plane because they are not useful in crowded areas.
StackModelFitExp: Contains the exponential fit parameters for stack detections brighter than some limit (
StackModelFitDeV: Contains the de Vaucouleurs fit parameters for stack detections brighter than some limit (
StackModelFitSer: Contains the Sersic fit parameters for stack detections brighter than some limit (
StackModelFitExtra: Contains various shape parameters for stack detections brighter than some limit (