No. |
Name |
Description |
|---|---|---|
| 1 | Sequence number | Running number for ease of reference, in strict order of image detections. |
| 2 | Isophotal flux | Standard definition of summed flux within detection isophote, except that a detection filter is used to define pixel connectivity and hence which pixels to include. This helps to reduce edge effects for all isophotally derived parameters. |
| 3 | X coord | Intensity-weighted isophotal centre-of-gravity in X. |
| 4 | Error in X | Estimate of centroid error. |
| 5 | Y coord | Intensity-weighted isophotal centre-of-gravity in Y. |
| 6 | Error in Y | Estimate of centroid error. |
| 7 | Gaussian sigma | These are derived from the three
general intensity-weighted second moments. The equivalence between them
and a generalised elliptical Gaussian distribution is used to derive: Gaussian sigma = (sigma(a)2+ sigma(b)2)1/2 ellipticity = 1.0-sigma(a)/sigma(b) position angle = angle of ellipse major axis w.r.t X axis. |
| 8 | Ellipticity | |
| 9 | Position angle | |
| 10 | Areal profile 1 | Number of pixels above a series of levels relative to local sky. The levels are set at T, 2T, 4T, 8T ... 128T, where T is the threshold. These can be thought of as a sort of poor man's radial profile. Note that for now, for deblended (i.e. overlapping) images, only the first areal profile is computed and the rest are set to -1, flagging the difficulty of computing accurate profiles. |
| 11 | Areal profile 2 | |
| 12 | Areal profile 3 | |
| 13 | Areal profile 4 | |
| 14 | Areal profile 5 | |
| 15 | Areal profile 6 | |
| 16 | Areal profile 7 | |
| 17 | Areal profile 8 | |
| 18 | Peak height | In counts relative to local value of sky - also zeroth order aperture flux. |
| 19 | Error in pk ht | |
| 20 | Aperture flux 1 | To be used if a single number is required to represent the flux for ALL objects. Basically aperture integration within core radius rc (in the FITS header), but modified to fit 'cores' simultaneously in case of overlapping images. Best selected using ~<FWHM> for site+instrument. Combined with later-derived aperture corrections for general photometry. |
| 21 | Error in flux | |
| 22 | Aperture flux 2 | A series of different aperture measures similar to parameter 20. Together with parameter 18 these give a simple curve-of-growth analysis. The set of 13 aperture radii are: 1/2×rc, 1/sqrt2×rc, rc, sqrt2×rc, 2×rc, 2sqrt2×rc, 4×rc, 4sqrt2×rc, 8×rc, 8sqrt2×rc, 16×rc, 16sqrt2×rc, 32×rc. The radius 4×rc ensures ~99% of PSF flux. Extras for generalised galaxy photometry further spaced by sqrt2 in radius to ensure correct sampling out to reasonable range of aperture sizes. Largest would be 32×rc i.e. ~30arcsec diameter. Note these are all corrected for pixels from overlapping neighbouring images. |
| 23 | Error in flux | |
| 24 | Aperture flux 3 | |
| 25 | Error in flux | |
| 26 | Aperture flux 4 | |
| 27 | Error in flux | |
| 28 | Aperture flux 5 | |
| 29 | Error in flux | |
| 30 | Aperture flux 6 | |
| 31 | Error in flux | |
| 32 | Aperture flux 7 | |
| 33 | Error in flux | |
| 34 | Aperture flux 8 | |
| 35 | Error in flux | |
| 36 | Aperture flux 9 | |
| 37 | Error in flux | |
| 38 | Aperture flux 10 | |
| 39 | Error in flux | |
| 40 | Aperture flux 11 | |
| 41 | Error in flux | |
| 42 | Aperture flux 12 | |
| 43 | Error in flux | |
| 44 | Aperture flux 13 | |
| 45 | Error in flux | |
| 46 | Petrosian radius | rp as defined in Strauss et al. (AJ, 124, 1810). |
| 47 | Kron radius | rk as defined in Bertin and Arnouts A&A Supp. 117 393. |
| 48 | FWHM radius | rfwhm average image radius at half peak height. |
| 49 | Petrosian flux | Flux within circular aperture to k1 × rp |
| 50 | Error in flux | |
| 51 | Kron flux | Flux within circular aperture to k2 × rk |
| 52 | Error in flux | |
| 53 | FWHM flux | Flux within circular aperture to k3 × rfwhm - simple alternative. |
| 54 | Error in flux | |
| 55 | Error bit flag | Bit pattern listing various processing error flags. |
| 56 | Sky level | Local interpolated sky level from background tracker. |
| 57 | Sky variance | Local estimate of variation in sky level around image. |
| 58 | Child/parent | Flag for parent or part of deblended deconstruct. |
The following are accreted directly after standard catalog generation. | ||
| 59 | RA | RA and Dec explicitly put in columns for overlay programs that cannot, in general, understand astrometric solution coefficients. Derived exactly from WCS in header and X, Y in parameters 3 & 5. |
| 60 | Dec | |
| 61 | Class'n stat 1 | Flag indicating probable classification: e.g. -1 stellar, +1 non-stellar, 0 noise. |
| 62 | Class'n stat 2 | An equivalent N(0,1) measure of how stellar-like an image is, used in deriving parameter 61 in a 'necessary but not sufficient' sense. |
From the further processing pipeline after deriving a suitable PSF. | ||
| 63 | PSF flux | Fitted flux from PSF. |
| 64 | Error in flux | |
| 65 | X coord | Updated PSF-fitted X centroid. |
| 66 | Error in X coord | |
| 67 | Y coord | Updated PSF-fitted Y centroid. |
| 68 | Error in Y coord | |
| 69 | PSF fit chi2 | Standard normalised variance of fit. |
| 70 | ndf(PSF) | No. of degrees of freedom for PSF fit. |
| 71 | 1D Sersic flux | Fitted flux for Sersic profile. |
| 72 | 1D scale length | Scale factor of fit. |
| 73 | 1D power index | Power law index of fit. |
| 74 | 1D Sersic fit chi2 | Standard normalised variance of fit. |
| 75 | ndf(S1) | No. of degrees of freedom for 1D Sersic fit. |
| 76 | 2D Sersic flux | Fitted flux for PSF-deconvolved 2D Sersic fit. |
| 77 | 2D scale length | Scale factor of fit. |
| 78 | 2D power index | Power law index of fit. |
| 79 | 2D Sersic fit chi2 | Standard normalised variance of fit. |
| 80 | ndf(S2) | No. of degrees of freedom for 1D Sersic fit. |
For numerical stability the Sersic fits will use the previously derived x-y coordinates | ||