This page is for building the dictionary of what the SExtractor terms mean, and how they should be represented as UCDs. The important set is the output columns, although the input parameters should really be given as UCDs where possible.

Where there is no exact UCD, give the closest and a suggested extension enclosed in question marks, eg FLUX_?ERR?. As far as I can tell, some of these might share the same UCD but have different units?

See http://cdsweb.u-strasbg.fr/doc/UCD.htx for information about UCDs and http://cdsweb.u-strasbg.fr/viz-bin/UCDs for a list of all them. Parameter descriptions are given in the SExtractor manual at http://www.eso.org/science/eis/eis_doc/sex2/sex2html/sex2_doc.html#SECTION00050000000000000000

Output Columns

SExtractor Term	UCD	Units	Notes
NUMBER	ID_NUMBER	-	Sequential number; applies to this result set only
FLUX_ISO	PHOT_FLUX ?	UNITS OF DATA	ISO is short for Isophotal; FLUX_ISO is the measured flux above an isophot specified by the detection threshold. The units may not be specified in the data
FLUXERR_ISO	PHOT_FLUX_?ERR
MAG_ISO
MAGERR_ISO
FLUX_ISOCOR			Corrected Isophotal Flux assuming a Gaussian Profile
FLUXERR_ISOCOR
MAG_ISOCOR
MAGERR_ISOCOR
FLUX_APER(1)		same as input image	Flux density in circular aperture; aperture(s) defined in the .sex file, which tag?
FLUXERR_APER(1)		as FLUX_APER	Error in FLUX_APER
MAG_APER(1)			As above but in magnitudes which magnitudes?
MAGERR_APER(1)		as MAG_APER	Error in MAG_APER
FLUX_AUTO
FLUXERR_AUTO
MAG_AUTO
MAGERR_AUTO
FLUX_BEST
FLUXERR_BEST
MAG_BEST
MAGERR_BEST
KRON_RADIUS
BACKGROUND
THRESHOLD
MU_THRESHOLD
FLUX_MAX
MU_MAX
ISOAREA_IMAGE
ISOAREA_WORLD
Position
XPEAK_IMAGE			(not given in default.param) x of pixel with max intensity
YPEAK_IMAGE			(not given in default.param) y of pixel with max intensity
XMIN_IMAGE	POS_CCD_X or POS_PHOTO_X		Rectangle boundary of source
YMIN_IMAGE	POS_CCD_X or POS_PHOTO_X		Rectangle boundary of source
XMAX_IMAGE	POS_CCD_X or POS_PHOTO_X		Rectangle boundary of source
YMAX_IMAGE	POS_CCD_X or POS_PHOTO_X		Rectangle boundary of source
Position - 1st order moments
X_IMAGE	POS_CCD_X or POS_PHOTO_X		1st order moment of profile
Y_IMAGE	POS_CCD_X or POS_PHOTO_X		1st order moment of profile
X_WORLD	POS_EQ_DEC ?		1st order moment of profile
Y_WORLD	POS_EQ_RA ?		1st order moment of profile
ALPHA_SKY
DELTA_SKY
ALPHA_J2000	POS_EQ_RA_MAIN
DELTA_J2000	POS_EQ_DEC_MAIN
ALPHA_B1950
DELTA_B1950
Position - 2nd order moments (eg for measuring spread)
X2_IMAGE	as 1st order
Y2_IMAGE	as 1st order
XY_IMAGE	as 1st order
X2_WORLD	as 1st order
Y2_WORLD	as 1st order
XY_WORLD			??
ERRX2_IMAGE			error in above
ERRY2_IMAGE			error in above
ERRXY_IMAGE			error in above
ERRX2_WORLD			error in above
ERRY2_WORLD			error in above
ERRXY_WORLD			error in above
Elipse parameters
CXX_IMAGE		pixels?	Elipse parameter
CYY_IMAGE		pixels?	Elipse parameter
CXY_IMAGE		pixels?	Elipse parameter
CXX_WORLD			as above but different units (undefined? depends on input image?)
CYY_WORLD
CXY_WORLD
ERRCXX_IMAGE			error in above
ERRCYY_IMAGE			error in above
ERRCXY_IMAGE			error in above
ERRCXX_WORLD			error in above
ERRCYY_WORLD			error in above
ERRCXY_WORLD			error in above
ELONGATION
ELLIPTICITY
Shape parameters
A_IMAGE	EXTENSION_DIAM	pixels?	Sem-major axis length
B_IMAGE	EXTENSION_SMIN	pixels?	Sem-minor axis length
A_WORLD	EXTENSION_DIAM		Sem-major axis length
B_WORLD	EXTENSION_SMIN		Sem-minor axis length
THETA_IMAGE
THETA_WORLD
THETA_SKY
THETA_J2000
THETA_B1950
ERRA_IMAGE
ERRB_IMAGE
ERRA_WORLD
ERRB_WORLD
ERRTHETA_IMAGE
ERRTHETA_WORLD
ERRTHETA_SKY
ERRTHETA_J2000
ERRTHETA_B1950
FWHM_IMAGE
FWHM_WORLD
ISO0
ISO1
ISO2
ISO3
ISO4
ISO5
ISO6
ISO7
FLAGS
IMAFLAGS_ISO(1)
NIMAFLAGS_ISO(1)
CLASS_STAR
VIGNET(5,5)

Extraction Parameters

SExtractor Term	UCD	Units	Notes
DETECT_TYPE		-	"CCD" or "PHOTO"
FLAG_IMAGE		-	filename for an input FLAG-image
DETECT_MINAREA		Pixels	minimum number of pixels above threshold
DETECT_THRESH		mag.arcsec-2	{sigmas} or {threshold},{ZP}
ANALYSIS_THRESH		mag.arcsec-2	{sigmas} or {threshold},{ZP}
FILTER		-	apply filter for detection ("Y" or "N")?
FILTER_NAME		-	name of the file containing the filter
DEBLEND_NTHRESH		-	Number of deblending sub-thresholds
DEBLEND_MINCONT		-	Minimum contrast parameter for deblending
CLEANY		-	Clean spurious detections? (Y or N)?
CLEAN_PARAM		-	Cleaning efficiency
MASK_TYPECORRECT		-	type of detection MASKing: can be one of "NONE", "BLANK" or "CORRECT"
Photometry Description
PHOT_APERTURES		pixels	MAG_APER aperture diameter(s) in pixels
PHOT_AUTOPARAMS		-	MAG_AUTO parameters: {Kron_fact},{min_radius}
SATUR_LEVEL		ADUs	level (in ADUs) at which arises saturation
MAG_ZEROPOINT		?	magnitude zero-point
MAG_GAMMA		-	gamma of emulsion (for photographic scans)
GAIN		e-/ADU	detector gain in e-/ADU.
PIXEL_SCALE		arcsec	size of pixel in arcsec (0=use FITS WCS info).
Star/Galaxy Separation
SEEING_FWHM		arcsec	stellar FWHM in arcsec
STARNNW_NAME		-	Neural-Network_Weight table filename
Background
BACK_SIZE		?	Background mesh: {size} or {width},{height}
BACK_FILTERSIZE		?	Background filter: {size} or {width},{height}
BACKPHOTO_TYPE		-	can be "GLOBAL" or "LOCAL" (*)
BACKPHOTO_THICK		?	thickness of the background LOCAL annulus (*)

There are other parameters to do with memory allocation and verbosity, which raises some extra thoughts - are we going to need a grid service ontology as well as an astronomy one, to exactly describe such things as "number of results" and verbosity, etc?

-- MartinHill - 19 Nov 2002