Data Model: zps

General Description
The zeropoints file is generated during the survey calibration and contains calibration metrics/zeropoints/flags at both the exposure and CCD levels. For each band (grizY), the same three HDUs are reported and only those for g-band are shown for clarity.
Approximate Size
22 MB
File Type
FITS
Sections

HDU1: g_exp

Exposure level calibration zeropoints, flags, and quality metrics for g-band exposures. The RESID and SCATTER measures that were used to decide if an exposure was "photometric" and to be included in the source catalog.

HDU Type
BINARY TABLE
HDU Size
156 KB
Data Table
NameTypeUnitDescription
SMF_FNfloat64J2000duplicate of MJD_OBS for historical reasons relating to PS1 heritage
MJD_OBSfloat64J2000Modified Julian date of observation
ZPfloat64inst. magPer exposure zeropoint to be added to measured instrumental magnitude in order to obtain AB magnitude
REASONint32Flag that is zero for ideal photometric conditions used in the photometric calibration (fit)
RESIDfloat32mag$2.7\sigma_{\rm IQR}$-clipped mean residual flux for calibration stars in the exposure relative to the model flux predicted by the photometric fit.
SCATTERfloat32mag$2.7\sigma_{\rm IQR}$-clipped standard deviation of the calibration stars residuals

HDU2: g_flf

Time-invariant flat-field for g-band derived on 256 x 256 pixel$^2$ sublocks fit during the photometric calibration. See Jupyter notebook in the release for how to map data format back into focal plane.

HDU Type
IMAGE
HDU Size
63 KB

HDU3: g_ccd

CCD level calibration flags and quality metrics for g-band exposures.

HDU Type
BINARY TABLE
HDU Size
4 MB
Data Table
NameTypeUnitDescription
SMF_FNcharJ2000string-ified version of MJD related to PS1 heritage; use MJD_OBS to identify exposures insetad.
MJD_OBSfloat64J2000Modified Julian date of observation
MNCHIPfloat32[64]magmean mag difference between sources detected on this chip, and those sources' mean magnitudes, after subtracting the equivalent offset for the whole exposure; i.e., how consistent is the mean photometry on this chip with that of the exposure?
SDCHIPfloat32[64]magstandard deviation in mag difference between sources detected on this chip and those sources' mean magnitudes
NSTARCHIPint32[64]number of good detections used on this chip in the photometric calibration process
CHMASKint32[64]Flag that is nonzero if a CCD is excluded from the catalog as a result of the photometric calibration.