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- Mar 20, 2020, 10:46:42 AM (6 years ago)
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analysis.tex (modified) (14 diffs)
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response.txt (modified) (5 diffs)
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trunk/doc/release.2015/ps1.analysis/analysis.tex
r41311 r41312 120 120 % \end{verbatim} 121 121 122 The 1.8m Pan-STARRS\,1 telescope is located on the summit of Haleakala122 The 1.8m Pan-STARRS\,1 telescope (PS1) is located on the summit of Haleakala 123 123 on the Hawaiian island of Maui. The wide-field optical design of the 124 124 telescope \citep{2004SPIE.5489..667H} produces a 3.3 degree field of view with … … 151 151 details of the telescope, surveys, and resulting science publications 152 152 are described by \cite{chambers2017}. 153 154 Since 2014 March, PS1 has been re-dedicated to a mission of searching 155 for hazardous asteroids, funded by the NASA NEO Program. Additional 156 partners collaborate with the Pan-STARRS team to harvest the transient 157 sources such supernovae and graviational wave counterparts 158 \note{REFS}. A second Pan-STARRS telescope (PS2), generally matching 159 the PS1 design \citep{Morgan2012} has since been constructed and has 160 been producing science results since early 2018. 153 161 154 162 %The Processing Version 3 (PV3) reduction represents the third full … … 337 345 image, or a group of related images representing the data read from 338 346 \textmod{the multiple chips of a mosaic 339 camera from} a single exposure. \textadd{In the IPP sequencing, this step is 340 called the \ippstage{chip} stage.} The images are expected to have already 347 camera from} a single exposure. The images are expected to have already 341 348 been detrended so that pixel values are linearly related to the flux. 342 349 The gain may be specified by the configuration system, or a variance … … 347 354 program \ippprog{ppImage} during the \ippstage{chip} analysis stage. 348 355 356 \textadd{In the standard IPP analysis, the initial stage of processing 357 is performed in parallel on each of the individual CCDs in the 358 camera. This so-called \ippstage{chip} stage analysis includes the 359 detrending of CCD image as well as the detection and analysis of 360 sources in the image using the basic version of \ippprog{psphot}. 361 The next stage of the analysis, the \ippstage{camera} stage, 362 consists of photometric and astrometric calibration.} 363 364 \textadd{After the calibrations are available, the detrended CCD images from 365 an entire exposure are geometrically transformed to a common pixel 366 grid in the \ippstage{warp} stage of the pipeline. The resulting 367 warped images are generated on a pre-define tessellation of the sky 368 which starts with projection centers spaced roughly 369 4\degrees\ across the sky. Around each of these projection centers, 370 a large regular pixel grid is defined, and then subdivided along 371 pixel boundaries into smaller units which are well-matched to the 372 memory footprint of our processing computesr. These smaller images, 373 called `skycells' are defined with 1 arcminute of overlap with their 374 neighbors to that any modest-sized object can be analysed entirely 375 on a single pixel grid. Note that the term skycell is used to 376 describe the particular subdivision of the sky. A typical exposure 377 from the GPC1 camera generates warp images on roughly 70 skycells. 378 We refer to the specific warped images from an exposure as `warps'.} 379 380 \textadd{Multiple warps for the same skycell are combined together in the 381 \ippstage{stack} stage of the IPP by co-adding the flux to generate 382 a deep `stack' image. Alternatively, one warp may be subtracted 383 from another warp of the same skycell, or a stack image may be 384 subtracted from a warp image, or indeed from another stack. These 385 subtraction operations are used to detect moving and transient 386 objects within the IPP. Different variants of \ippprog{psphot} are 387 used for the source detection and analysis for each of these 388 different analysis stages.} 389 349 390 The variant called \ippprog{psphotStack} accepts a set of images, each 350 391 representing the same patch of sky \textadd{(with pixels aligned)} in 351 a different \textmod{filter. This version was used for the analysis 352 of the deep ``stacks'' (co-added images combining multiple 353 observations of the same field) produced by the IPP \ippstage{stack} 354 stage. Nominally, 355 the full $grizy$ filter set was used for the analysis} of the PS1 PV3 stack 356 images, though where insufficient data were available in a given 357 filter, a subset of these filters was processed as a group. As 358 discussed in detail below, the \ippprog{psphotStack} analysis includes the 359 capability of measuring forced PSF photometry in some filter images 360 based on the position of sources detected in the other filters. It 361 also includes an option to convolve the set of images to a single, 362 common PSF size across the filters for the purpose of fixed aperture 363 photometry. 392 a different \textmod{filter. This version was used in the IPP for the 393 analysis of the deep ``stacks'' produced by the IPP \ippstage{stack} 394 stage. Nominally, the full $grizy$ filter set was used for the 395 analysis} of the PS1 PV3 stack images, though where insufficient 396 data were available in a given filter, a subset of these filters was 397 processed as a group. As discussed in detail below, the 398 \ippprog{psphotStack} analysis includes the capability of measuring 399 forced PSF photometry in some filter images based on the position of 400 sources detected in the other filters. It also includes an option to 401 convolve the set of images to a single, common PSF size across the 402 filters for the purpose of fixed aperture photometry. 364 403 365 404 Another variant of \ippprog{psphot} used in the PV3 analysis is called … … 1638 1677 1639 1678 \subsubsection{Fast Ensemble PSF Fitting} 1679 \label{sec:ensemble.fitting} 1640 1680 1641 1681 Before the detailed analysis of the sources is performed, it is … … 2900 2940 \end{figure*} 2901 2941 2902 \section{Forced Photometry Modes}2942 \section{Forced Warp Analysis} 2903 2943 \label{sec:psf.forced.fit} 2904 2944 … … 2951 2991 2952 2992 The IPP analysis solves this problem by starting with the sources 2953 detected in the stack images and performing forced photometry on the 2954 individual warp images used to generate the stack, and then combining 2955 the resulting measurements to determine a high-quality average value. 2956 This forced-photometry analysis is performed using the 2993 detected in the stack images and performing \textmod{a highly 2994 constrained analysis on the individual warp images used to generate 2995 the stack, and then combining the resulting measurements to 2996 determine a high-quality average value. We consider all of these 2997 measurements to be ``forced'' because of the strong prior 2998 constraints from the stack.} This analysis is performed using the 2957 2999 \ippprog{psphotFullForce} variant of \ippprog{psphot}. 2958 3000 2959 In this program, the positions of sources are loaded from the output 2960 catalog of the stack photometry. Candidates PSF stars are 2961 pre-identified as those stars used to generate the PSF model in the 2962 stack photometry analysis. A PSF model is generated for each input 2963 warp image based on those stars; PSF stars which are excessively 2964 masked on a particular image are not used to model the PSF. The PSF 2965 model is fitted to all of the known source positions in the warp 2966 images. Aperture magnitudes, Kron magnitudes, and moments are also 2967 measured at this stage for each warp. Note that the flux measurement 2968 for a faint, but significant, source from the stack image may be at a 2969 low significance (less than the $5\sigma$ criterion used when the 3001 \subsection{Forced PSF Photometry} 3002 3003 \textmod{PSF photometry is measured for all objects detected in the 3004 stack using the positions determined by the stack photometry 3005 analysis.} Candidate PSF stars are pre-identified as those stars 3006 used to generate the PSF model in the stack photometry analysis. A 3007 PSF model is generated for each input warp image based on those stars; 3008 PSF stars which are excessively masked on a particular image are not 3009 used to model the PSF. The \textadd{normalization of the} PSF model 3010 is fitted to all of the known source positions in the warp images to 3011 determine the PSF fluxes. This measurement is performed simultaneously 3012 for all sources in the image at once using the method described above 3013 (Section~\ref{sec:ensemble.fitting}). 3014 3015 \textmod{Aperture fluxes, Kron fluxes}, and moments are also measured at 3016 this stage for each warp. Note that the flux measurement for a faint, 3017 but significant, source from the stack image may be at a low 3018 significance (less than the $5\sigma$ criterion used when the 2970 3019 photometry is not run in this forced mode) in any individual warp 2971 3020 image; the measured flux may even be negative due to statistical 2972 3021 fluctuations. When combined together, these low-significance 2973 measurements result in a significant measurement as the signal-to-noise2974 increases with the combination of more data.3022 measurements result in a significant measurement as the 3023 signal-to-noise increases with the combination of more data. 2975 3024 2976 3025 Individual warp images are processed independently with separate … … 3022 3071 normalization value is determined. The integrated flux, flux error, 3023 3072 and the $\chi^2$ value for each grid point are recorded. 3073 \textadd{This analysis is performed on the warp images one object at a 3074 time with the other objects in the image subtracted according to 3075 the best model currently known.} 3024 3076 3025 3077 For a given galaxy, the result is a collection of $\chi^2$ values, … … 3071 3123 For the Pan-STARRS $3\pi$ PV3 analysis, we have measured the full set 3072 3124 of KSB lensing parameters for all objects with measured second moments 3073 (i.e., ,excluding saturated stars, suspected cosmic rays, and other3125 (i.e., excluding saturated stars, suspected cosmic rays, and other 3074 3126 likely defects) of the data to enable both lensing studies and binary 3075 3127 / multiple star searches. Here we describe the measurements as 3076 3128 performed within \ippprog{psphot}, reviewing the mathematical 3077 3129 framework as described by \cite{1995ApJ...449..460K} and 3078 \cite{1998ApJ...504..636H}. 3130 \cite{1998ApJ...504..636H}. \textadd{Just like the forced PSF 3131 photometry and the constrained galaxy models above, this analysis is 3132 performed by measuring the KSB lensing parameters on the individual 3133 warp images and averaging these measurements for each object.} 3079 3134 3080 3135 The goal of the KSB technique is to measure the intrinsic ellipticity … … 3099 3154 $e_1$ values. An object with a position angle on the 45\degree\ lines 3100 3155 between the pixel axes will have large positive or negative values of 3101 $e_2$ and low absolu ate values of $e_1$.3156 $e_2$ and low absolute values of $e_1$. 3102 3157 3103 3158 Note that in our analysis of the second moments, we are applying a … … 3211 3266 sm}_\alpha$) and the shear polarizability ($X^{\rm sh}_{\alpha 3212 3267 \beta}$, $e^{\rm sh}_\alpha$) for all objects on each of the warp 3213 images. We have also selected only the PSF stars from the images and 3214 interpolated a smoothed version of these parameters to the location of 3215 the objects, using the grid described above to interpolate the PSF 3216 parameters. We also determine the interpolated PSF ellipticities 3268 images. \textmod{We have also selected only the PSF stars from the images and 3269 interpolated a smoothed version of these parameters from the PSF stars 3270 to the locations of 3271 all objects, using the grid described above to interpolate the 3272 parameters. We then determine the ellipticities of the stars} 3217 3273 ($e^*_1, e^*_2$) from the equivalent smooth grid. Thus, for every 3218 3274 object in the $3\pi$ survey, we are able to report the PSF and object … … 3241 3297 which generates those image. 3242 3298 3299 \note{Note that this article is limited to the analysis of the 3300 difference image detections, and that additional work is needed to 3301 filter real/bogus. Refer to Denneau et al 2013 PASP for the MOPS analysis. Refer 3302 to the Wright et al papers for the SNe classifications (& other 3303 papers?). Mention Yuan \& Akerloff 2008.} 3304 3305 \note{mention the 3 difference image modes (WW, WS, SS)} 3306 3307 % https://ui.adsabs.harvard.edu/abs/2013PASP..125..357D/abstract 3308 3243 3309 The analysis of the difference image follows the same basic steps as 3244 3310 other \ippprog{psphot} versions with some minor modifications (see … … 3247 3313 performed. The PSF model construction stage is not possible in the 3248 3314 difference image due to the lack of valid sources. Instead, the PSF 3249 model fromis generated from the positive image, after PSF-matching3315 model is generated from the positive image, after PSF-matching 3250 3316 but before the subtraction is performed. Because we do not expect to 3251 3317 have a large number of sources, only a single source detection pass is … … 3367 3433 repeated measurements of the same exposures). 3368 3434 3435 % PS2 reference: 3436 % https://ui.adsabs.harvard.edu/abs/2012SPIE.8444E..0HM/abstract 3437 3369 3438 \acknowledgments 3370 3439 -
trunk/doc/release.2015/ps1.analysis/response.txt
r41310 r41312 518 518 are averaged. 519 519 520 ** We agree that the organization of this section could be improved, 521 but we disagree a bit with the proposal. We consider all of these 522 analyses to be forced in that the fits are highly constrained by the 523 stack priors, with their positions (for PSFs and the lensing anaysis) 524 and most of the structural parameters fixed. In the extended galaxy 525 analysis, each of the grid steps is completely forced, just like in 526 forced PSF photometry. By using the term 'forced' to describe this 527 process, we would like to make it clear that, for each grid position, 528 the parameters (except normalization) are completely constrained. 529 530 We have renamed Section 6 as Forced Warp Analysis and split out the 531 PSF vs extended source analysis sections as recommended. We added 532 some explanation at the end of the section to explain what we mean by 533 'forced'. 534 520 535 - The general description of the section should end with "variant of psphot", 521 536 with the motivation being written such that it applies to both the 522 537 averaged forced photometry on stars and the averaged single-epoch fits 523 538 for galaxies 539 ** see previous 524 540 525 541 Sec 6.1 (now 6.2): … … 532 548 - The terms "skycell" and "warp image" are first used here without 533 549 definition. Are warp images the same as CAMERA and CHIP? 534 ** 550 ** Updated Section 2 to outline the relevant processing stages and 551 define 'warp', 'skycell', and 'stack' more cleanly. 535 552 536 553 - For the forced photometry on single epoch images, is this a joint 537 554 fit for overlapping objects? 538 Are overlapping galaxy models subtracted first? "The PSF model is 539 fitted..." -> "The amplitude of the PSF model is fitted as the flux..." 555 ** for the galaxy models, no. The galaxy model fits are measured on 556 each object with the other objects subtracted. Text added to this 557 effect in Section 6.1 558 559 Are overlapping galaxy models subtracted first? 560 ** yes, see above. 561 562 "The PSF model is fitted..." -> "The amplitude of the PSF model is fitted as the flux..." 563 ** fixed the wording here and also clarified below that we measure 564 Kron and aperture fluxes as well. 540 565 541 566 Sec 6.2 (now 6.3): … … 543 568 parameters are an average of all of the single-epoch measurements. 544 569 This should be stated upfront, and then again at the end of the subsection 545 clarifying how the PSF systematics are removed. Phrases like 570 clarifying how the PSF systematics are removed. 571 572 Phrases like 546 573 "interpolated PSF ellipticities" are confusing, when I *think* what's 547 574 being used are "interpolated star ellipticities". 575 ** reworded this to make the analysis clearer 548 576 549 577 - Was this lensing code used in any of the GREAT challenge papers, … … 554 582 - "ie,," -> "ie," 555 583 " absoluate" -> "absolute" 584 ** fixed both 556 585 557 586 Sec 7: … … 561 590 If these questions are covered in other Pan-STARRS papers, please reference 562 591 them here. 592 **** 563 593 564 594 - A basic piece of information that should be given is whether the differencing 565 595 is performed on pairs of images, or single (warp) images compared to 566 596 image stacks. 597 **** 567 598 568 599 - "model from is" -> "model is" 600 ** fixed 569 601 570 602 Conclusions:
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