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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 magnitude is inferred from the growth curve (enclosed flux vs. radius).

Contents

The starting point for the PS1 data archive is at Pan-STARRS1 data archive home page.

Definition

Look up the formal definition (Kron 1980, ApJS 43, 305). 

The Kron 1980 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:

  • Kron Radius determined from smoothed image
  • start with isophotal aperture at sky level
  • measure moments
  • redefine aperture to be 6x 1st radial moment
  • re-measure moments
  • Kron flux is measured inside 2.5 * 1st radial moment
  • 1.0 * 1st radial moment and 4.0 * 1st radial moment fluxes are also measured as KRON_INNER and KRON_OUTER

Be aware that by definition Kron magnitudes do NOT encompass the total flux from an object, and in DR1 no attempt is made to correct the Kron fluxes for this missing light. Some information on the size of this effect for galaxies can be seen in this article, but very roughly expect 10% of the flux to be missing.

Values Available

Kron parameters are listed in several different tables, depending on their origin (warp images, stack images, mean values, etc.) The PS1 MeanObject table fields table includes:

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.

 

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.

 

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.


The tables below with multi-epoch measurements are not included in the DR1 database but are included here for completeness.

PS1 Detection table fields contains:

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.

 

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.

 

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.

 
  

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