Photo's Main Tabular Output
First some outputs which describe the object as a whole:
-
id
-
An id for the object within the frame; this id is the same as the object's
row number in the table, and is used to tie the
OBJC_IO
and
ATLAS_IMAGE
tables together.
-
parent
-
The
id
number of the object's parent, or -1 if it is a primary detection.
-
ncolor
-
The number of colours present in this table; should always be 5 during
normal operations.
-
objc_type
-
An enum giving the object's overall classification. Current possibilities are:
- UNK
-
An object of unknown type (the default).
- CR
-
A cosmic ray
- DEFECT
-
Some indeterminate chip defect.
- GALAXY
-
A galaxy
- GHOST
-
A ghost produced by the 2.5m optics.
- KNOWNOBJ
-
A known object (from e.g. FIRST or ROSAT); its position and size are
inputs to photo.
- STAR
-
A Star
- TRAIL
-
A satellite, aeroplane, meteorite, or asteroid trail.
- SKY
-
A pseudo-object; a location where no object was detected in any
of the survey bands.
These categories are repeated below for each band; the algorithm used
to arrive at the overall classigfication is TBD.
-
catID
-
A catalog id number associated with KNOWNOBJs. We may want to revisit how
this is done when some real known object catalogues are available.
-
objc_flags
-
The union of certain of the flag bits set in each individual band
(see discussion of
flags
below). Specifically, if the flags
BLENDED, CHILD, EDGE, INTERP, MANYPETRO, NOPETRO, NOTCHECKED, or SATUR
are set in any band, they are also set in objc_flags
.
-
objc_rowc, objc_colc, objc_rowcErr, objc_colcErr
-
The canonical position of the object (and 1-sigma errors),
in the r' coordinate system. If an object is detected in r', this is
the r' centre; otherwise it's a suitable average of the bands where the
object was detected (Pixels).
The following fields are calculated for each band:
-
rowc, colc, rowcErr, colcErr
-
The position of the object (and 1-sigma errors) in each band. In the case
that an object is not detected in a given band (say f'), the position is
taken to be the r' position offset to the f' coordinate system
(if detected in r'), and a suitable average of the other bands otherwise.
(Pixels).
We will describe the position assigned in the r' as the r' position,
even if the object was not in fact detected in r'.
-
sky, skyErr
-
The sky level (and the 1-sigma), at the position of the object.
(Counts/pixel^2).
-
psfCounts, psfCountsErr
-
The PSF-flux (and the 1-sigma error), at the position of the
object (Counts).
An aperture correction,
to a fixed radius, calculated by the PSP, has been applied.
-
fiberCounts, fiberCountsErr
-
The 3''-counts (and the 1-sigma error), at the r' position of the
object. These counts are supposed to be corrected to a canonical seeing,
but this is not currently (Dec 1997) being done.
-
petroRad, petroRadErr
-
The Petrosian radius (and the 1-sigma error),
measured using the r' position of the object (Pixels).
-
petroCounts, petroCountsErr
-
The Petrosian counts (and the 1-sigma error) within f_3 r_{P,r'} of
the r' centre. Suitable measures must be taken if the object is not
detected in r' (Counts).
-
petroR50, petroR50Err
-
The Petrosian 50%-light radius (and 1-sigma error) (Pixels).
-
petroR50, petroR90Err
-
The Petrosian 90%-light radius (and 1-sigma error) (Pixels).
-
Q, U, QErr, UErr
-
The values of <col^2/r^2 - row^2/r^2> and <col row/r^2>
(and their 1-sigma errors), measured within r_{P,r'}. These are
estimators of (a - b)/(a + b)cos(2 phi) and (a - b)/(a + b)sin(2 phi),
and are named by analogy to the usual Stokes parameters.
For more details, see
The Estimation of Object's Ellipticities.
-
nprof
-
The number of points in the three succeeding measures of the radial profile,
each of which refers to annuli with fixed outer radii of
{ 0.56, 1.69, 2.58, 4.41, 7.51, 11.58, 18.58, 28.55, 45.50, 70.51, 110.5,
172.5, 269.5, 420.5, 657.5 } pixels, that is
{ 0.23 0.68 1.03 1.76 3.00 4.63 7.43 11.42 18.20 28.20 44.21 69.00
107.81 168.20 263.00 } arcseconds. These radii correspond to circular
apertures enclosing an integral number of pixels: { 1, 9, 21, 61, 177, 421,
1085, 2561, 6505, 15619, 38381, 93475, 228207, 555525, 1358149 }.
-
profMean
-
The mean surface brightness within the innermost
nprof
annuli, with
fixed radii given above; these fluxes may be used to recover the annular
counts exactly (counts/pixel).
-
profMed
-
The `median' surface brightness within the innermost
nprof
annuli, with
fixed radii given above (counts/pixel).
-
profErr
-
An estimate of the uncertainty in the profiles (counts/pixel);
note that this is not the photon noise (which can be recovered from
profMean
), but an estimate of the true uncertainty allowing for
contamination by stars, HII regions, etc.
iso_rowc, iso_colc, iso_a, iso_b, iso_phi,
iso_rowcErr, iso_colcErr, iso_aErr, iso_bErr, iso_phiErr,
iso_rowcGrad, iso_colcGrad, iso_aGrad, iso_bGrad, iso_phi
-
The centre, major and minor axes, and position angle of a certain isophote
(Pixels).
These are determined from the 2-dimensional extracted profile.
The
Grad
quantities are correction terms allowing us to correct
for errors in the photometric calibration.
r_deV, I_deV, ab_deV, phi_deV,
r_deVErr, I_deVErr, ab_deVErr, phi_deVErr
-
Parameters of the de Vaucouleurs profile that best fits the radial profile (as
determined by the cell array), and errors.
The
r
and I
parameters are the effective radius and the surface brightness at that point.
r_exp, I_exp, ab_exp, phi_exp,
r_expErr, I_expErr, ab_expErr, phi_expErr
-
Parameters of the exponential profile that best fits the radial profile (as
determined by the cell array), and errors.
The
r
and I
parameters are the effective radius and the surface brightness at that point.
-
star_L, exp_L, deV_L
-
Likelihoods for the fits of the model by the PSF, an exponential disk, and
a de Vaucouleurs profile. More specifically, the values quoted the
probabilities of finding a value of chi^2 at least as large as that
found for the model fits.
-
fracPSF
-
The fraction of the total light in the profile that can be assigned to
a point source. Not currently calculated.
-
texture
-
A measure of the roughness of the object, based on the residuals after
inverting the image and subtracting.
-
flags
-
Some more information about how the processing went. Note that these
values are also used in
objc_flags
, where they are used
to summarise information about the object as a whole, rather than a
single band.
Current possibilities are:
- OBJECT1_NOTDETECTED
-
Object wasn't detected in this band
- OBJECT1_BRIGHT
-
Object was found by findBrightObjects
- OBJECT1_BINNED
-
Object contains pixels that were only marked as part of an object after
the frame had been binned, and the object finder rerun
- OBJECT1_EDGE
-
Object was too close to edge of frame to be measured
- OBJECT1_PEAKCENTER
-
Given centre is position of peak pixel, rather than an MLE fit
- OBJECT1_NOPROFILE
-
The object was too small for us to be able to measure a radial profile
- OBJECT1_TOO_LARGE
-
The object is too large for us to measure its profile (i.e. it extends
beyond a radius of approximately 263 arcseconds;
see SDSS Profile Extraction.)
- OBJECT1_BAD_RADIAL
-
The radial profile extends beyond where its S/N first drops to (??) 1.
- OBJECT1_NOSTOKES
-
Object has no measured stokes parameters.
- OBJECT1_BADSKY
-
The sky level is so bad that the highest pixel in the object is very
negative; far more so than a mere non detection. No further analysis is
attempted.
- OBJECT1_ELLIPFAINT
-
The object's centre is fainter than the isophote whose shape is desired,
so its properties are not measured.
Information about measuring Petrosian quantities:
- OBJECT1_NOPETRO
-
The object has no Petrosian radius
- OBJECT1_MANYPETRO
-
The object has more than one Petrosian radius; the largest found is adopted
- OBJECT1_PETROFAINT;
-
At least one possible Petrosian radius was rejected as the surface brightness
at r_P was too low. If NOPETRO isn't set, an (different) acceptable Petrosian
radius was found.
- OBJECT1_PETRO_SMALL
-
Object has no Petrosian radius; used
f5
instead.
- OBJECT1_PETRO_BIG
-
Not currently used
- OBJECT1_MANYR50
-
An object has more than one 50% light radius
- OBJECT1_MANYR90
-
An object has more than one 90% light radius
- OBJECT1_INCOMPLETE_PROFILE
-
The circle r = r_{P,r'} intersects the edge of the frame
Information about pixels contained in the object:
- OBJECT1_CR
-
Object contains at least one pixel flagged as belonging to a cosmic ray.
- OBJECT1_INTERP
-
The object contains at least one pixel that has been interpolated
- OBJECT1_NOTCHECKED
-
The object contains at least one pixel that is marked as having not been
searched for objects
- OBJECT1_SATUR
-
The object contains at least one saturated pixel
- OBJECT1_SUBTRACTED
-
Bright wings were subtracted from this object (presumably a star).
Various flags associated with the deblender:
- OBJECT1_BLENDED
-
Object was found to be blended, and has children
- OBJECT1_CHILD
-
Object is a deblended child
- OBJECT1_NODEBLEND
-
No deblending was attempted, although the BLENDED flag is set
- OBJECT1_DEBLENDED_AS_PSF
-
The deblender treated the object as a PSF
- OBJECT1_DEBLEND_PRUNED
-
The deblender deleted some of the peaks that we in the parent object
-
type
-
The type assigned to the object in this colour; the possibilities are
described for the
objc_type
field.