Kron photometry is determined from the observed (smoothed) profile of each Detection. A Kron radius is determined for all objects, irrespective of whether they are point sources or not, and the total magnitude is inferred from the growth curve (enclosed flux vs. radius).
Look up the formal definition (Kron 1980, ApJS 43, 305). The paper shows how to define a nominal magnitude for an extended object on the basis of the shape of the light profile.
In the PanSTARRS implementation, the definition of the Kron radius and Kron magnitude is carried out as follows (from the PS1 guide (Kron Parameters) [PS1 wiki login required]:
Kron parameters are listed in the Detection table as follows:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
kronFlux | Janskys | REAL | 4 | -999 | Kron (1980) flux. |
kronFluxErr | Janskys | REAL | 4 | -999 | Error on Kron (1980) flux. |
kronRad | arcsec | REAL | 4 | -999 | Kron (1980) radius. |
StackObjectThin contains:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
gKronMag | AB magnitudes | REAL | 4 | -999 | Kron (1980) magnitude from g filter stack detection |
gKronMagErr | AB magnitudes | REAL | 4 | -999 | Error in Kron (1980) magnitude from g filter stack detection. |
and similar entries in the same row for rizy filters.
StackObjectAttributes contains:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
gKronFlux | Janskys | REAL | 4 | -999 | Kron (1980) flux from g filter stack detection. |
gKronFluxErr | Janskys | REAL | 4 | -999 | Error in Kron (1980) flux from g filter stack detection. |
gKronRad | arcsec | REAL | 4 | -999 | Kron (1980) radius from g filter stack detection. |
and similar entries in the same row for rizy filters.
MeanObject contains:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
gMeanKronMag | AB magnitudes | REAL | 4 | -999 | Mean Kron (1980) magnitude from g filter detections. |
gMeanKronMagErr | AB magnitudes | REAL | 4 | -999 | Error in mean Kron (1980) magnitude from g filter detections. |
gMeanKronMagStd | AB magnitudes | REAL | 4 | -999 | Standard deviation of Kron (1980) magnitudes from g filter detections. |
gMeanKronMagNpt | dimensionless | SMALLINT | 2 | -999 | Number of measurements included in mean Kron (1980) magnitude from g filter detections. |
and similar entries in the same row for rizy filters.
ForcedWarpMeasurement contains:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
FkronFlux | Janskys | REAL | 4 | -999 | Kron (1980) flux. |
FkronFluxErr | Janskys | REAL | 4 | -999 | Error in Kron (1980) flux. |
FkronRad | arcsec | REAL | 4 | -999 | Kron (1980) radius. |
ForcedMeanObject contains:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
gFKronFlux | Janskys | REAL | 4 | -999 | Mean Kron (1980) flux from forced single epoch g filter detections. |
gFKronFluxErr | Janskys | REAL | 4 | -999 | Error in mean Kron (1980) flux from forced single epoch g filter detections. |
gFKronFluxStd | Janskys | REAL | 4 | -999 | Standard deviation of Kron (198) fluxes from forced single epoch g filter detections. |
gFKronMag | AB magnitudes | REAL | 4 | -999 | Magnitude from mean Kron (1980) flux from forced single epoch g filter detections. |
gFKronMagErr | AB magnitudes | REAL | 4 | -999 | Error in magnitude from mean Kron (1980) flux from forced single epoch g filter detections. |
and similar entries in the same row for rizy filters.
DiffDetection contains:
Name | Unit | Data Type | Size | Default Value | Description |
---|---|---|---|---|---|
DkronFlux | Janskys | REAL | 4 | -999 | Kron (1980) flux. |
DkronFluxErr | Janskys | REAL | 4 | -999 | Error in Kron (1980) flux. |
DkronRad | arcsec | REAL | 4 | -999 | Kron (1980) radius. |
Most of the information contained here is based on the PS1 Guide http://ps1sc.ifa.hawaii.edu/PS1wiki/index.php/PS1Guide#Kron_parameters (requires PS1 wiki login). Information on the contents of the Table is obtained from the PSPS Schema Browser at http://web01.psps.ifa.hawaii.edu/PSI/schema_browser.php?describeTable=Detection (requires PSPS login). The STScI verison of the schema browser is at http://plps3v.stsci.edu/PSI/schema_browser.php.
The original definitions presumably are from Kron (1980): http://adsabs.harvard.edu/abs/1980PhyS...21..652K
A modern implementation is described, e.g., for 2MASS at: http://www.ipac.caltech.edu/2mass/releases/allsky/doc/sec4_5e.html.
If you have more specific information on the exact definitions used in PanSTARRS processing, please add a comment or email stefano@stsci.edu.
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