Matched Sources catalog

A visit is a set of N consecutive (zero dead time) exposures of the same field of view (no slewing or dithering between exposures). All the individual (epoch) catalogs are matched by coordinates, and the matched source catalog is available. The object is saved in an HDF5 file, in which each dataset represents a column name (e.g., RA), and contains a matrix of size (Nepoxh X Nsrc).

Description

The Matched sources catalog is generated by cross-matching the sources' position (by RA, Dec) with a search radius of 1.5''. This radious is measured relative to the position of the source in the first image it appears. If a source is not detected in one/many epochs, then its properties are populated with NaN.

The source catalogs also contain objects from forced photometry (indicated by the FORCED column). In order to avoid mix up of forced and non-forced sources, FORCED sources are matched separately.

Available column names

The object contains matrices (Nepoch X Nsrc) with the following properties. In addition to these properties, a vector of JD corresponding to the mid exposure time is stored in the object.

Property	Units	Description
RA	deg	J2000.0 right ascension corresponding to the PSF-fit X,Y position of the source.
Dec	deg	J2000.0 declination corresponding to the PSF-fit X,Y position of the source.
X	pix	PSF-fit X position of the source.
Y	pix	PSF-fit Y position of the source.
X1	pix	First-moment X position of the source.
Y1	pix	First-moment Y position of the source.
X2	pix $^2$	Weighted second central moment, $\langle X^2 \rangle$, of the source.
Y2	pix $^2$	Weighted second central moment, $\langle Y^2 \rangle$, of the source.
XY	pix $^2$	Weighted second central cross moment, $\langle XY \rangle$, of the source.
SN	—	Signal-to-noise ratio of the PSF fit.
SN_1	—	Signal-to-noise ratio assuming the source is a delta function.
SN_2	—	Signal-to-noise ratio assuming the source is an unresolved PSF, as measured in the image.
MAG_PSF	mag	Calibrated magnitude corresponding to the PSF-fit flux.
MAGERR_PSF	mag	Photometric uncertainty of MAG_PSF, including PSF-fit flux uncertainty but excluding calibration uncertainty unless otherwise specified.
PSF_CHI2DOF	—	Reduced $\chi^2$ of the PSF fit, $\chi^2/\mathrm{dof}$.
MAG_APER_3	mag	Calibrated magnitude in aperture 3, with radius 6 pix. The calibration is likely derived using the transmission-fitting method and includes aperture correction.
MAGERR_APER_3	mag	Photometric uncertainty of MAG_APER_3, including source Poisson noise and background noise, but excluding calibration uncertainty.
FLUX_APER_3	$e^{-}$	Annulus-background-subtracted aperture flux of the source, measured in aperture 3, with radius 6 pix.
FLAGS	—	32-bit mask propagated from the mask image (all pixels within 3 pix radius from the source position). See bitmask description in: Image bit mask page.
BACK_IM	$e^{-}$	Background at the source position, measured from the background image.
VAR_IM	$(e^-)^2$	Variance at the source position, measured from the variance image.
BACK_ANNULUS	$e^{-}$	Local background around the source, estimated as the median pixel value in an annulus around the source.
STD_ANNULUS	$e^{-}$	Standard deviation of the local background, measured from the pixels in an annulus around the source.
FORCED	logical	A flag indicating if the source is a forced photometry source (true) or not (false).