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trunk/doc/release.2015/ps1.analysis/analysis.tex (modified) (19 diffs)
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trunk/doc/release.2015/ps1.analysis/analysis.tex
r40608 r40609 545 545 * PM\_SOURCE\_MODE\_PSFMODEL & 0x00000001 & Source fitted with a psf model (linear or non-linear) \\ 546 546 * PM\_SOURCE\_MODE\_EXTMODEL & 0x00000002 & Source fitted with an extended-source model \\ 547 548 549 550 551 552 553 PM\_SOURCE\_MODE\_BLEND & 0x00000100 & Source is a blend with other sources\\554 555 556 557 558 559 560 561 562 563 PM\_SOURCE\_MODE\_BELOW\_MOMENTS\_SN & 0x00040000 & moments not measured due to low S/N\\564 565 566 567 568 569 570 571 572 PM\_SOURCE\_MODE\_SIZE\_SKIPPED & 0x10000000 & size could not be determined\\547 * PM\_SOURCE\_MODE\_FITTED & 0x00000004 & Source fitted with non-linear model (PSF or EXT; good or bad) \\ 548 * PM\_SOURCE\_MODE\_FAIL & 0x00000008 & Fit (non-linear) failed (non-converge, off-edge, run to zero) \\ 549 * PM\_SOURCE\_MODE\_POOR & 0x00000010 & Fit succeeds, but low-SN, high-Chisq, or large (for PSF -- drop?) \\ 550 * PM\_SOURCE\_MODE\_PAIR & 0x00000020 & Source fitted with a double psf \\ 551 * PM\_SOURCE\_MODE\_PSFSTAR & 0x00000040 & Source used to define PSF model \\ 552 * PM\_SOURCE\_MODE\_SATSTAR & 0x00000080 & Source model peak is above saturation \\ 553 * PM\_SOURCE\_MODE\_BLEND & 0x00000100 & Source is a blend with other sources$^1$ \\ 554 * PM\_SOURCE\_MODE\_EXTERNAL & 0x00000200 & Source based on supplied input position \\ 555 * PM\_SOURCE\_MODE\_BADPSF & 0x00000400 & Failed to get good estimate of object's PSF \\ 556 * PM\_SOURCE\_MODE\_DEFECT & 0x00000800 & Source is thought to be a defect \\ 557 * PM\_SOURCE\_MODE\_SATURATED & 0x00001000 & Source is thought to be saturated pixels (bleed trail) \\ 558 * PM\_SOURCE\_MODE\_CR\_LIMIT & 0x00002000 & Source has crNsigma above limit \\ 559 * PM\_SOURCE\_MODE\_EXT\_LIMIT & 0x00004000 & Source has extNsigma above limit \\ 560 * PM\_SOURCE\_MODE\_MOMENTS\_FAILURE & 0x00008000 & could not measure the moments \\ 561 * PM\_SOURCE\_MODE\_SKY\_FAILURE & 0x00010000 & could not measure the local sky \\ 562 * PM\_SOURCE\_MODE\_SKYVAR\_FAILURE & 0x00020000 & could not measure the local sky variance \\ 563 x PM\_SOURCE\_MODE\_BELOW\_MOMENTS\_SN & 0x00040000 & moments not measured due to low S/N.$^1$ \\ 564 * PM\_SOURCE\_MODE\_BIG\_RADIUS & 0x00100000 & poor moments for small radius, try large radius \\ 565 * PM\_SOURCE\_MODE\_AP\_MAGS & 0x00200000 & source has an aperture magnitude \\ 566 * PM\_SOURCE\_MODE\_BLEND\_FIT & 0x00400000 & source was fitted as a blend \\ 567 * PM\_SOURCE\_MODE\_EXTENDED\_FIT & 0x00800000 & full extended fit was used \\ 568 * PM\_SOURCE\_MODE\_EXTENDED\_STATS & 0x01000000 & extended aperture stats calculated \\ 569 * PM\_SOURCE\_MODE\_LINEAR\_FIT & 0x02000000 & source fitted with the linear fit \\ 570 * PM\_SOURCE\_MODE\_NONLINEAR\_FIT & 0x04000000 & source fitted with the non-linear fit \\ 571 * PM\_SOURCE\_MODE\_RADIAL\_FLUX & 0x08000000 & radial flux measurements calculated \\ 572 x PM\_SOURCE\_MODE\_SIZE\_SKIPPED & 0x10000000 & size could not be determined$^2$ \\ 573 573 PM\_SOURCE\_MODE\_ON\_SPIKE & 0x20000000 & peak lands on diffraction spike \\ 574 574 PM\_SOURCE\_MODE\_ON\_GHOST & 0x40000000 & peak lands on ghost or glint \\ 575 575 PM\_SOURCE\_MODE\_OFF\_CHIP & 0x80000000 & peak lands off edge of chip \\ 576 \hline 577 \multicolumn{3}{l}{$^1$ not used for DR1 or DR2.} \\ 578 \multicolumn{3}{l}{$^2$ should not normally occur, does it?} \\ 576 579 \hline 577 580 \end{tabular} … … 1038 1041 centroid is used to center the window function. 1039 1042 1043 For sources with peak flux above the saturation limit, the moments are 1044 generally poorly measured if the aperture defined by $\sigma_w$ is 1045 used. For these sources, the quality of the measurment is compromised 1046 by the saturation. However, it is still useful to estimate the first 1047 and second moments of the source in order to allow a crude measurement 1048 of the brightness from the wings of the source. In this case, a 1049 larger aperture, 3 times the standard aperture, is used to make a 1050 crude estimate. For such sources, the flag bit 1051 \code{PM_SOURCE_MODE_BIG_RADIUS} is set and the source is ignored in 1052 all analyses below except for the analysis applied to very bright 1053 stars (Section~\ref{sec:very.bright.star}). 1054 1040 1055 If the measured centroid coordinates ($x_0, y_0$) differ from the peak 1041 1056 coordinates be a large amount (1.5$\sigma_w$), then the peak is 1042 identified as being of poor quality (\code{infoFlag} bit 1043 \code{MOMENTS_FAILURE}) and is skipped in further analyses. In such 1044 as case, it is likely that the `peak' was identified in a region of 1045 flat flux distribution or many saturated or edge pixels. 1057 identified as being of poor quality and is skipped in further 1058 analyses; the flag bit 1059 \code{PM_SOURCE_MOMENTS_FAILURE} is set for such sources. In such 1060 a case, it is likely that the `peak' was identified in a region of 1061 flat flux distribution or many saturated or edge pixels. During the 1062 analysis of the moments, the background (``sky'') model is also examined for the 1063 location of each source. The value of the background and the variance 1064 of the background are recorded for each source. In some cases, the 1065 sky model or the variance is not well defined at the location of a 1066 specific sources (e.g., due to an extrapolation failure). In these 1067 cases, the flag bits \code{PM_SOURCE_SKY_FAILURE} or 1068 \code{PM_SOURCE_SKYVAR_FAILURE} are set as appropriate and the 1069 measurement of the moments is skipped. 1046 1070 1047 1071 In addition to the moments above, the 1st and half-radial moments, … … 1254 1278 produce a single peak. To avoid detecting a peak from the unresolved 1255 1279 cosmic rays, sources which have second-moments very close to 0 are 1256 ignored. 1280 ignored. For these sources, the flag bit \code{PM_SOURCE_MODE_DEFECT} 1281 is set. 1257 1282 1258 1283 Once a peak has been detected in this plane, the centroid and second … … 1260 1285 pixels of this centroid are selected as candidate PSF sources in the 1261 1286 image. 1287 1288 When the second moments are measured, \ippprog{psphot} also counts the 1289 number of saturated pixels within the analysis aperture. If more than 1290 a single saturated pixel is found, and if the second moments of that 1291 object are more than one standard deviation larger than the clump 1292 identified above, this source is identified as a highly saturated star 1293 and marked with the flag bit \code{PM_SOURCE_MODE_SATSTAR}. Sources 1294 which have more than a single saturated pixel, but for which the 1295 second moments do not exceed the above limits are marked as likely 1296 saturated regions (e.g., bleed trails). These sources are skipping in 1297 most additional analyses and are marked with the flag bit 1298 \code{PM_SOURCE_MODE_SATURATED}. 1262 1299 1263 1300 \begin{figure}[htbp] … … 1304 1341 snuck into the sample). Sources whose model parameters are rejected 1305 1342 by this iterative fitting technique are also marked as invalid PSF 1306 sources and ignored in the later PSF model fitting stages. 1343 sources and ignored in the later PSF model fitting stages. Sources 1344 which are actually used to define the PSF model for a given image have 1345 the flag bit \code{PM_SOURCE_MODE_PSFSTAR} set. 1307 1346 1308 1347 The order of the fit or number of grid samples is modified if the … … 1354 1393 is measured here, with a more detailed correction measured after all 1355 1394 source analysis is performed (see 1356 Section~\ref{sec:aperture.correction}). 1395 Section~\ref{sec:aperture.correction}). Sources for which the 1396 aperture magnitude is measured have the flag bit 1397 \code{PM_SOURCE_MODE_AP_MAGS} set. These aperture magnitudes are 1398 stored in the DVO field \code{Measure.Map} and exported to the PSPS as 1399 a flux in Janskies in the field \code{Detection.apFlux}. The radius 1400 (in arcseconds) 1401 of the aperture used for each exposure is reported in PSPS as 1402 \code{Detection.apRadius}, while the unmasked fraction of the aperture 1403 is reported in PSPS as \code{Detection.apFillF}. 1404 1405 When the PSF and aperture photometry for a source is measured, two 1406 additional quantities are measured which are useful to assess the 1407 quality of the measurements. First, the mask image is examined and the 1408 number of unmasked pixels is summed, weighted by the normalized PSF 1409 model. The resulting quantity, \code{PSF_QF} has a value between 0.0 1410 (totally masked) and 1.0 (totally unmasked). Elsewhere in the IPP 1411 system, we use this value to filter out detections which are 1412 unreliable due to the masking. For a generous cut, leaning toward 1413 completeness at the cost of some lower quality measurements, 1414 \code{PSF_QF} $> 0.85$ is used in some contexts; in other cases, we 1415 require \code{PSF_QF} $> 0.95$ to ensure a high-quality measurement 1416 \citep[see for example the calculation of average photometry 1417 in][]{magnier2017.calibration}. The second quantity is related to 1418 the first: \code{PSF_QF_PERFECT} uses all mask values to assess the 1419 quality factor, while \code{PSF_QF} uses only the ``bad'' mask bit 1420 values (see Section~\ref{sec:image.preparation}). 1357 1421 1358 1422 \subsection{Bright Source Analysis} … … 1458 1522 PSF. Sources for which a PSF model has been fitted (whether or not 1459 1523 this is retained as the best model in the end) has the flag field 1460 \code{PM_SOURCE_MODE_PSFMODEL} set. 1524 \code{PM_SOURCE_MODE_PSFMODEL} set. All sources which are included in 1525 the ensemble linear fit have the flag bit 1526 \code{PM_SOURCE_MODE_LINEAR_FIT} set, including those for which the 1527 model is not the PSF. 1461 1528 1462 1529 \subsubsection{Radial Profile Wings} … … 1544 1611 Kron magnitudes and called \code{extNsigma}. If \code{extNsigma} is 1545 1612 larger than \code{PSPHOT.EXT.NSIGMA.LIMIT} (3.0), the source is 1546 considered to be extended. 1613 considered to be extended and the flag bit 1614 \code{PM_SOURCE_MODE_EXT_LIMIT} is set for the source. 1547 1615 1548 1616 Cosmic rays are identified by a combination of the Kron magnitude and … … 1557 1625 identified as a cosmic ray and the associated pixels are masked. 1558 1626 These values are tuned empirically for the PV3 analysis based on 1559 cosmic rays identified in the GPC1 images. 1627 cosmic rays identified in the GPC1 images. Sources which are 1628 determined to the a cosmic ray in this manner have the flag bit 1629 \code{PM_SOURCE_MODE_DEFECT} set. 1630 1631 The pixels of any suspected cosmic ray identified above are examined 1632 in additional detail to make a final judgement. The Laplacian edge 1633 detection algorithm based on \cite{2001PASP..113.1420V} is used to 1634 check for sharp edges in the flux distribution. If the sharpness 1635 exceeds a defined limit, then the pixels are masked and the flag bit 1636 \code{PM_SOURCE_MODE_CR_LIMIT} is set for the source. 1560 1637 1561 1638 % Mminor < 0.8 && SN > 7 … … 1584 1661 non-linear fitting. The sources are fitted in their S/N order, 1585 1662 starting with the brightest and working down to the user-specified 1586 limit, with the other sources subtracted as discussed above. 1663 limit, with the other sources subtracted as discussed above. All 1664 sources for which a non-linear PSF model has been attempted have the 1665 flag bit \code{PM_SOURCE_MODE_FITTED} set, regardless of the quality 1666 of that fit. 1667 1668 Since the PSF model describes the variation of the PSF across the 1669 image, the parameters used to fit a specific object are drawn from the 1670 model at the position corresponding to the object centroid. 1671 Occasionally, a PSF model for an image may not be well determined in 1672 all regions of the image. For example, not enough bright stars were 1673 available across the full range of the image to model the PSF and the 1674 resulting fitted parameters yield non-sensical solutions in areas 1675 where detected (fainter) sources are found. In such cases, the PSF 1676 fitting is skipped and the flag bit \code{PM_SOURCE_MODE_BADPSF} is set. 1587 1677 1588 1678 For the PSF model fitting, only pixels within a circular aperture … … 1594 1684 window radius is $7 \times \sigma_w$. 1595 1685 1596 Sources which are blended with other sources are fitted together as a1686 Sources which are blended with other sources may be fitted together as a 1597 1687 set of PSFs. Blended objects are identified by first searching for 1598 1688 objects for which the PSF fit windows overlap. For a group of such … … 1604 1694 blends of this next object. All objects in the image are tested as 1605 1695 possible blends. A single multi-source fit is performed on each group 1606 of blended peaks. 1696 of blended peaks. Sources which are identified as members of a 1697 blended group have the flag bit \code{PM_SOURCE_MODE_BLEND} set, while 1698 those for which a blended PSF fit succeeds have the flag bit 1699 \code{PM_SOURCE_MODE_BLEND_FIT} set. {\em Note that for DR1 \& DR2, 1700 this option was not used because it tended to prevent galaxies from 1701 being fitted as extended objects; the rules for identifying blended 1702 stars and galaxies will be revisited in future re-analyses.} 1607 1703 1608 1704 %% Once a solution has been achieved for a source, \ippprog{psphot} attempts to … … 1670 1766 1671 1767 Sources which are pass the above tests are marked as having a valid 1672 non-linear PSF model fit (\code{PM_SOURCE_MODE_SATSTAR}). Among these 1673 sources, those for which the peak flux is greater than the saturation 1674 limit (see Section~\ref{sec:image.preparation}) are marked as 1675 saturated stars (\code{PM_SOURCE_MODE_SATSTAR}). These model fits 1676 should be considered with caution, but the fluxes and positions may 1677 have some validity. 1768 non-linear PSF model fit with the flag bit 1769 \code{PM_SOURCE_MODE_NONLINEAR_FIT}. Among these sources, those for 1770 which the peak flux is greater than the saturation limit (see 1771 Section~\ref{sec:image.preparation}) are marked as saturated stars 1772 (\code{PM_SOURCE_MODE_SATSTAR}). These model fits should be 1773 considered with caution, but the fluxes and positions may have some 1774 validity. 1678 1775 1679 1776 % \citep[see the discussion in][regarding the masking of saturated … … 1708 1805 as a valid PSF source. Otherwise, the double-PSF model is rejected 1709 1806 and the source is fitted with the available non-PSF model or models. 1807 Sources for which a double-PSF model is fitted have the flag bit 1808 \code{PM_SOURCE_MODE_PAIR} set. 1710 1809 1711 1810 \subsubsection{Non-PSF Sources} … … 1914 2013 saved as equal-length vectors in the FITS table (\code{PROF_FLUX} and 1915 2014 \code{PROF_FILL}). The values of the radial bins are saved in the 1916 output file FITS header (\code{RMIN_NN}, \code{RMAX_NN}). 2015 output file FITS header (\code{RMIN_NN}, \code{RMAX_NN}). 1917 2016 1918 2017 % \note{these profiles are not saved in PSPS} … … 1963 2062 Petrosian Flux, we can calculate two other interesting radii: $R_{50}$ 1964 2063 and $R_{90}$, the radii inside which 50\% and 90\% of the total 1965 Petrosian flux is contained. 2064 Petrosian flux is contained. Sources for which the Petrosian 2065 parameters are successfully measured have the flag bit 2066 \code{PM_SOURCE_MODE_EXTENDED_STATS} set. 2067 1966 2068 1967 2069 \subsubsection{Convolved Galaxy Model Fits} … … 2111 2213 We next perform 3 Levenberg-Marquardt minimization fits allowing the 2112 2214 shape parameters ($R_{xx}$, $R_{yy}$ , $R_{xy}$) and the normalization 2113 to be fitted, holding the centroid ($x_0, y_0$), S\'ersic index $n$, and2114 sky constant. In these fits, the index $n$ is set to the minimum2215 to be fitted, holding the centroid ($x_0, y_0$), S\'ersic index $n$, 2216 and sky constant. In these fits, the index $n$ is set to the minimum 2115 2217 value previously calculated as well as values halfway to the next, and 2116 2218 previous, values in the grid above. E.g., if the minimum fitted index 2117 value is 3.0, then the LMM fits are performed using $n$ = 2.5, 3.0, 3.5.2118 The resulting $\chi^2$ values are then used to perform quadratic2219 value is 3.0, then the LMM fits are performed using $n$ = 2.5, 3.0, 2220 3.5. The resulting $\chi^2$ values are then used to perform quadratic 2119 2221 interpolation to find the index $n$ which produces the locally minimum 2120 2222 $\chi^2$ value. Finally, this best-fit index value is held constant 2121 2223 while Levenberg-Marquardt minimization is used to find the best fit 2122 values of all other parameters. 2224 values of all other parameters. Sources for which a convolved galaxy 2225 model fit was successful have the flag bit 2226 \code{PM_SOURCE_MODE_EXTENDED_FIT} set. 2123 2227 2124 2228 % Graham & Driver : Graham A. W., Driver S. P. 2005, PASA 22, 118 … … 2204 2308 wasteful. We only calculate the circular apertures out to the second 2205 2309 aperture larger than the ``sky radius'' (defined in 2206 Section~\ref{sec:radial.profile}), but we calculate photometry for 2207 at least the smallest 4 apertures. 2310 Section~\ref{sec:radial.profile}), but we calculate photometry for at 2311 least the smallest 4 apertures. Sources for which photometry in these 2312 fixed aperture are calculated have the flag bit 2313 \code{PM_SOURCE_MODE_RADIAL_FLUX} set. 2208 2314 2209 2315 % at least out to aperture # RADIAL_AP_MIN (= 4), but no further than … … 2422 2528 2423 2529 Individual warp images are processed independently with separate 2424 executions of the \ippprog{psphotFullForce} program. Once all of the 2425 forced photometry measurements (for point sources as well as galaxies, 2426 discussed below) are completed for all of the warps which contributed 2427 to a stack image, the measurements are combined together by other 2428 portions of the IPP system. The PSF photometry measurements are 2429 combined in the context of the DVO database system 2430 \citep{magnier2017.datasystem}, including recalibration of the zero 2431 points for the individual warp. 2530 executions of the \ippprog{psphotFullForce} program. Sources which 2531 are loaded by \ippprog{psphotFullForce} for analysis are marked with 2532 the flag bit \code{PM_SOURCE_MODE_EXTERNAL}. This bit is also used to 2533 mark user-supplied sources loaded for analysis by the regular version 2534 of \ippprog{psphot}. Once all of the forced photometry measurements 2535 (for point sources as well as galaxies, discussed below) are completed 2536 for all of the warps which contributed to a stack image, the 2537 measurements are combined together by other portions of the IPP 2538 system. The PSF photometry measurements are combined in the context 2539 of the DVO database system \citep{magnier2017.datasystem}, including 2540 recalibration of the zero points for the individual warp. 2432 2541 2433 2542 \subsection{Forced Galaxy Models}
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