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 r_{c} (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×r_{c}, 1/sqrt2×r_{c}, r_{c}, sqrt2×r_{c}, 2×r_{c}, 2sqrt2×r_{c}, 4×r_{c}, 4sqrt2×r_{c}, 8×r_{c}, 8sqrt2×r_{c}, 16×r_{c}, 16sqrt2×r_{c}, 32×r_{c}. The radius 4×r_{c} 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×r_{c} 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 | r_{p} as defined in Strauss et al. (AJ, 124, 1810). |
47 | Kron radius | r_{k} as defined in Bertin and Arnouts A&A Supp. 117 393. |
48 | FWHM radius | r_{fwhm} average image radius at half peak height. |
49 | Petrosian flux | Flux within circular aperture to k1 × r_{p} |
50 | Error in flux | |
51 | Kron flux | Flux within circular aperture to k2 × r_{k} |
52 | Error in flux | |
53 | FWHM flux | Flux within circular aperture to k3 × r_{fwhm} - 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 chi^{2} | 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 chi^{2} | 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 chi^{2} | 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 |