Basic Use of SExtractor Catalogs With TweakReg - II (ISR 15
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1. WCS version to use in processing proc_unit native Units used during processing coeffs True Use header based distortion coefficients context True Create context image during final drizzle group Single extension or group to be combined cleaned build False Create multi extension output file for final drizzle crbit 4096 Bit value for CR ident in DQ array stepsize 16 Step size for drizzle coordinate computation resetbits 4096 Bit values to reset in all input DQ arrays num_cores None Max CPU cores to use n lt 2 disables None quto decide in_memory False Process everything in memory to minimize disk I 0 i STATE OF INPUT FILES restore False Copy input files FROM archive directory for processing preserve True Copy input files to archive directory if not already archived overwrite False Copy input files into archive overwriting if required clean False Delete temporary files after completion STEP 1 STATIC MASK static True Create static bad pixel mask from the data static_sig 4 6 Sigmatrms below mode to clip for static mask STEP 2 SKY SUBTRACTION skysub True Perform sky subtraction skywidth 6 1 Bin width for sampling sky statistics cin sigma skystat median Sky correction statistics parameter skylower None Lower Limit of usable data for sky always in electrons skyupper None Upper Limit of usable data for sky always in electrons sky2. number of pixels in stack number of lines in buffer can be QUIET NORMAL or FULL Write XML file Y N Filename for XML output Number of simultaneous threads for Appendix C Basic SExtractor default conv file PONY NORM 3x3 all ground convolution mask with FWHM 2 pixels eNe NAN eNe 21 Appendix D Basic SExtractor default nnw file pew Neural Network Weights for the SExtractor star galaxy classifier V1 3 9 for profile parameters 1 for seeing Stellarity index 8 8 to 1 0 i ol Seeing FWHM range from 0 025 to 5 5 images must have 1 5 lt FWHM lt 5 pixels nputs utputs Optimized for Moffat profiles with 2 lt beta 4 3 1 3 3 4 2 4 1 5 2 3 8 3 1 1616 1 56604e 00 03477e 00 22480e 01 62594e 01 57424e 00 81641e 68 1933e 81 31793e 88 26336e 61 75075e 00 41923e 01 65598e 00 70059e 00 88008e 08 60008e 88 48265e 00 69561e 00 12804e 00 29127e 00 96469e 01 53747e 00 09484e 01 94240e 00 70056e 00 25399e 00 64997e 00 56997e 00 65695e 00 44564e 00 16188e 00 50750e 01 10950e 00 34775e 01 12216e 00 87426e 08 64165e 00 20105e 01 75325e 00 65808e 01 76373e 00 22367e 00 1 6 18845e 00 3 87912e 01 4 4 2 3 1 5 24675e 00 34497e 00 11242e 00 61857e 61 16003e 08 37436e 00 28330e 01 68814e 00 08277e 01
3. yoffset 4 Initial guess for Y offset pixels CATALOG FITTING PARAMETERS fitgeometry rscale Fitting geometry residplot both Plot residuals from fit nelip 3 Number of clipping iterations in fit sigma 3 6 Clipping limit in sigma units ylimit None Upper Lower limit in pixels for residplot labelsize 8 Font size in points for plot labels 25 Appendix G Penultimate Last Iteration TweakReg Run Parameters _task_name_ tweakreg input flc fits Input files name suffix or Glist refimage Filename of reference image exclusions Filename for source exclusions catalogs updatewcs False Update WCS keywords of input images writecat True Write out source catalogs clean False Remove intermediate files verbose False Print extra messages during processing runfile tweakreg log Filename of processing log expand_refcat False Expand reference catalog with new sources enforce_user_order True Align images in user specified order interactive True Allow interactive display of plots UPDATE HEADER updatehdr False Update headers of input files with shifts wesname TWEAK Name of updated WCS HEADERLET CREATION headerlet False Create headerlet for solution attach True Create headerlet FITS extension hdrfile Filename for headerlet FITS file clobber False Overwrite existing headerlet FITS file hdrname Unique name HDRNAME for head
4. Instrument Science Report ACS 2015 05 Basic Use of SExtractor Catalogs With TweakReg II Ray A Lucas May 27 2015 ABSTRACT The TweakReg task in the DrizzlePac software package for aligning and drizzling images is an effective tool for the initial processing of HST images However the internal object finding software which it uses to generate catalogs to be used for object matching and alignment ImageFindPars is based on the well known stellar oriented daofind routine and though it is appropriate for most images there are some for which the task is not well suited such as some extragalactic fields which have lots of galaxies but almost no stars and in some cases if taken over long time baselines even the few stars present may have moved due to proper motion thereby making them unsuitable for use in image alignment In that case other object detection programs such as SExtractor can be used to generate external catalogs of primarily galaxies which can then be fed to the TweakReg task Even multiwavelength morphological differences may make some galaxies less suitable than others for use in image alignment and registration The basic use of simple external SExtractor catalogs with the DrizzlePac TweakReg task is described here using ACS WFC data as an example This includes updating geometric distortion files initial drizzling to make cosmic ray cleaned images the set up and use of required SExtractor files to generate SExtractor c
5. 74542e 00 74367e 01 44913e 01 51865e 00 40683e 00 29492e 01 46526e 00 67404e 00 05210e 01 55417e 00 57258e 03 71128e 00 01687e 00 37540e 01 5 3 1 1 8 1 6 7 3 4 4 5 29571e 08 2 22453e 01 65570e 00 55944e 00 42290e 00 60878e 02 75767e 00 04535e 02 54368e 01 36502e 01 62933e 88 73127e 01 55400e 01 46316e 08 22 a 1 90741e 00 6 1 5 69605e 08 8 2 8 1 61342e 02 74856e 08 84558e 08 88080e 01 29310e 00 87826e 01 18568e 82 13747e 88 92138e 61 59195e 01 22353e 00 oO 1 44058e 00 1 59549e 01 7 45967e 00 7 1 89044e 00 27910e 01 31957e 01 84541e 00 18946e 61 33623e 62 94117e 61 16163e 08 89186e 01 42038e 00 15505e 00 22811e 00 52395e 01 19118e 01 30403e 02 08468e 01 89198e 61 62946e 00 23195e 00 29122e 00 75543e 01 91906e 00 22919e 00 N 4 42851e 01 64942e 00 1 8 1 1 42119e 00 9 64769e 81 27734e 00 36564e 01 61592e 82 12716e 82 61361e 06 71561e 82 49380e 01 72828e 01 22250e 01 5 4 1 7 2 13514e 61 1 71712e 01 36745e 01 35502e 00 4 2 30052e 00 69824e 00 01231e 00 54052e 00 07067e 01 13749e 01 32028e 00 Appendix E Basic SExtractor default params file SExtractor default param for output catalog filets to become Drizzlepac tweakreg in
6. BACK_FILTERSIZE 3 Background filter lt size gt or lt width gt lt height gt BACKPHOTO_TYPE GLOBAL can be GLOBAL or LOCAL Check Image CHECKIMAGE_TYPE OBJECTS can be NONE BACKGROUND BACKGROUND_RMS MINIBACKGROUND MINIBACK_RMS BACKGROUND FILTERED OBJECTS OBJECTS SEGMENTATION or APERTURES Give this in the command line instead CHECKIMAGE_NAME jabu lfyq_crelean_exti_check fits Filename for the check image CHECK IMAGE_NAME ms Filename for the check image Memory change with caution MEMORY _OBISTACK 3088 number of objects in stack MEMORY_PIXSTACK 300888 number of pixels in stack MEMORY_BUFSIZE 1624 number of lines in buffer Miscellaneous VERBOSE_TYPE NORMAL can be QUIET NORMAL or FULL WRITE_XML N Write XML file Y N XML_NAME sex xml Filename for XML output NTHREADS 4 Number of simultaneous threads for NOTE In Appendix F G and H updatehdr may sometimes be set to True Yes or False No depending on which version of the software and which interface you are using Also Appendices G amp H are only examples They may not represent your last 2 TweakReg runs since you may conceivably try still more things to improve solutions 24 Appendix F Initial TweakReg Run Parameters
7. _task_name_ tweakreg input flc fits Input files name suffix or list refimage Filename of reference image exclusions Filename for source exclusions catalogs updatewcs False Update WCS keywords of input images writecat False Write out source catalogs clean False Remove intermediate files verbose False Print extra messages during processing runfile tweakreg log Filename of processing log expand_refcat False Expand reference catalog with new sources enforce_user_order True Align images in user specified order interactive True Allow interactive display of plots UPDATE HEADER updatehdr False Update headers of input files with shifts wesname TWEAK Name of updated WCS HEADERLET CREATION headerlet False Create headerlet for solution attach True Create headerlet FITS extension hdrfile Filename for headerlet FITS file clobber False Overwrite existing headerlet FITS file hdrname Unique name HDRNAME for header let author Author name for creator of headerlet descrip Short description of headerlet solution catalog Name of catalog used for headerlet solution history Name of ASCII file containing history for header let OPTIONAL SHIFTFILE OUTPUT shiftfile True Create output shiftfile outshifts shifts verl txt Filename of generated shiftfile outwes shifts verl_wes fits Filename of shiftfile reference WCS
8. expkeyword NOTE We have turned on Step 7 the final drizzle here for our own curiosity even before the fine alignment with TweakReg just to see how a rough first version of a final image might look in this case where all of the images in all of the filters were taken in the same visit but this need not be done for the process we have described here 19 Appendix B Basic SExtractor default sex file Parameters Default configuration file for SExtractor 2 8 6 EB 2010 11 16 Modified to produce output files for use as input files after further editing to the Drizzlepac tweakreg task Edit the CATALOG_NAME below to use the distinctive part of the file name for each unique image in the group of images which you are cataloging Do this for each new catalog run once for each image at least as the SExtractor software seems to run on MEF files for now Edit the CHECKIMAGE_NAME below to use the distinctive part of the file name for each unique image in the group of images which you are cataloging Do this for each new catalog run once for each image at least as the SExtractor software seems to run on MEF files for now The CATALOG_NAME and CHECKIMAGE_NAME should be in syne and have the same rootname for each of your runs so that you have a catalog and checkimage with the same rootname as each other for each of your successive runs Edit the default param file to make any
9. parameters and version of the input catalogs to match the conditions which produced the most desired results Remember also that you should not update the WCS again or you will undo the geometric corrections you have applied earlier To begin the alignment process TweakReg expects a file which lists the images to be aligned the _flc fits images along with the catalogs from each chip of the crclean fits images in the form flc fits crclean chipl cat crclean chip2 cat thus jabuOlfvq_flc fits jabuOlfvq_crclean_extl cat jabu0lfvq_crclean_ext4 cat jabuOlgfq_flc fits jabuOlgfq_crclean_extl cat jabuOlgfq_crclean_ext4 cat jabu0lgmq_flc fits jabu0lgmq_crclean_extl cat jabu01gmq_crclean_ext4 cat jabu0lgsq_flc fits jabu0lgsq_crclean_extl cat jabu0lgsq_crclean_ext4 cat jabu0lgyq_flc fits jabuOlgyq_crclean_extl cat jabu0lgyq_crclean_ext4 cat jabuOlhcq_flc fits jabu0lhcq_crclean_extl cat jabu0lhcq_crclean_ext4 cat This file may be called by any name as long as that name is given as the parameter value to the catfile parameter in the TweakReg task In this case even though we are feeding it our own external SExtractor catalogs we have chosen to name it just as the TweakReg task names it by default when it uses its own internally generated catalogs from the ImageFindPars task coords_catfile lis We begin the iterative process by running TweakReg with mostly default parameter values to first see what kind of result we get that way and
10. 2 8 6 at http www astr tohoku ac jp akhlaghi sextractor_notes html Holwerda B SExtractor for Dummies at http astroa physics metu edu tr MANUALS sextractor Guide2source_extractor pdf DrizzlePac tasks and usage DrizzlePac tasks and usage Gonzaga et al 2012 The DrizzlePac Handbook Available on line http documents stsci edu hst HST_overview documents DrizzlePac DrizzlePac cover html 16 STScI DrizzlePac Web Site http www stsci edu hst HST_overview drizzlepac AAS Posters at DrizzlePac web site Lucas R A 2012 AstroDrizzle Utilizing New CALACS Products AAS Anchorage Alaska _http www stsci edu hst HST_overview drizzlepac resources ral_aas anchorage_2012 template v7_Lucas pdf Lucas R A Hilbert B and Hack W 2013 Using SExtractor With the DrizzlePac Tweakreg Software for Aligning and Combining Sources in HST ACS Images AAS Long Beach California http www stsci edu hst HST_overview drizzlepac resources Lucas_AAS pdf ISRs Lucas R A and Hilbert B 2015 Basic Use of SExtractor Catalogs With TweakReg I Instrument Science Report ACS 2015 04 17 Appendix A Initial AstroDrizzle Input Parameters _task_name_ astrodrizzle input flc fits Input files name suffix or list output Rootname for output drizzled products runfile astrodrizzle log File for logging the processing updatewcs False Update the WCS keywords weskey
11. and checkimage as appropriate in the default sex file before each issuance of the command to run SExtractor As determined by the default params file the specific format of the output catalog in this example is given at the head of the output catalog and is the following with the first number on the left representing the column number in the output 1 X_IMAGE Object position along x pixel 2 Y_IMAGE Object position along y pixel 3MAG AUTO Kron like elliptical aperture magnitude mag 4CLASS_STAR S G classifier output 5 NUMBER Running object number 6 FLAGS Extraction flags The most critical components of the output are x and y measurements of the objects plus magnitude or flux information Depending on whether the flux values in the images are expressed in terms of counts or counts per second the magnitude zeropoint may be expressed in different ways In the case of this example the images were in counts so the magnitude zeropoint was calculated as M 2 5 log expoure time where M was a value obtained from http www stsci edu hst acs analysis zeropoints zpt py which is the web page for the ACS zero point calculator This will enable later optional automatic trimming within TweakReg of the input list for matching based on magnitude limits In this case the ST Mag system was used but it could easily have been any of several other magnitude systems which are offered as options in the ACS zero point calculator The
12. bandpasses for example However simple removal of objects with high residuals may also work very well since they are after all seemingly problematic in at least some of the images and catalogs In fact although a tedious process which most would not want to try in most circumstances in the case of badly mis aligned images with grossly bad pointing info in the header etc due to something like a guide star problem during acquisition manual measurement and generation of catalog entries for objects in such an image which are then inserted into the input catalog s can be an effective way of correcting the header info in those images and bringing them into a close enough spatial concordance with the others that the TweakReg task can then be used in subsequent iterations to more finely align them to other images at similar pointings In fact in even more labor intensive fashion an entire manually measured and manually edited list of catalog object positions could be created for each image and run through TweakReg in this manner if it was advantageous but that is as said a very labor intensive exercise which is usually much better automated in some way if possible and so we only mention the possibility of it here and leave the rest to the reader as an exercise if so desired Step 6 Re running TweakReg to Update the Headers of Files to Be Aligned Once a solution has been found that the user deems acceptable or at least the best possible t
13. changes you desire or that tweakreg requires for the output catalog which you will edit and then feed to the tweakreg task You will typically use the catalogs from the first file as the reference image for all the rest and may copy it to a name reflective of that as such or may leave it with its regular name but just specify it as the reference image in Drizzlepac tweakreg when you run that Ray A Lucas 31 May 2012 Catalog Give this in the command line instead CATALOG_NAME jabu 1f vq_erc lean_ext1 cat name of the output catalog CATALOG_NAME e name of the output catalog CATALOG_TYPE ASCII_HEAD NONE ASCII ASCII_LHEAD ASCII_SKYCAT ASCII_VOTABLE FITS_1 6 or FITS_LDAC PARAMETERS_NAME default param name of the file containing catalog contents Extraction DETECT_TYPE CCD CCD linear or PHOTO with gamma correction DETECT_MINAREA 5 minimum number of pixels above threshold DETECT_MINAREA 3 minimum number of pixels above threshold DETECT_THRESH 1 5 lt sigmas gt or lt threshold gt lt 2P gt in mag arcsec 2 DETECT_THRESH 7 8 lt sigmas gt or lt threshold gt lt 2P gt in mag arcsec 2 ANALYSIS_THRESH 1 5 lt sigmas gt or lt threshold gt lt 2P gt in mag arcsec 2 FILTER Y apply filter for detection Y or NY FILTER_NAME default cony name of
14. final_wht_type IVM as is needed for input to SExtractor but for now we will ignore the use of weight maps with SExtractor in this basic example The use of weight maps with SExtractor a usage which tends to yield better positional accuracy though not inherently difficult is a more advanced topic which will be addressed further in for example Hubble Frontier Fields technical documentation For now for the main points being made in our basic example we do not need an image of this sort although use of weight images with SExtractor often with iteration ultimately tends to yield better positional accuracy We will therefore in this example continue on with the use of the _crclean fits images which we have now created with our initial AstroDrizzle run which has produced a single crclean fits image for each single input _flc fits image so that there is a one to one correspondence between these two image types Appendix A lists our input parameters in detail for our initial run of AstroDrizzle to create these _crclean fits images Step 3 Run SExtractor to Produce Object Catalogs for Alignment Here we assume that the reader has either already downloaded and installed SExtractor according to standard directions or will do so and will refer as needed to further documentation referenced in this article We have used SExtractor version 2 8 6 in this case It handles multi extension FITS files in a more user friendly fashion than earlier vers
15. the file containing the filter DEBLEND_NTHRESH 32 Number of deblending sub thresholds DEBLEND_MINCONT 6 885 Minimum contrast parameter for deblending CLEAN T Clean spurious detections Y or NY CLEAN_PARAM 1 6 Cleaning efficiency MASK_TYPE CORRECT type of detection MASKing can be one of NONE BLANK or CORRECT Continued on next page 20 SExtractor defaul sex file continued Fee NC Teac Re ee ITT PHOT_APERTURES PHOT_AUTOPARAMS 5 2 5 3 5 PHOT_PETROPARAMS 2 0 3 5 Photometry MAG_APER aperture diameter s in pixels MAG_AUTO parameters lt Kron_fact gt lt min_radius gt MAG_PETRO parameters lt Petrosian_fact lt min_radius gt This is the average ACS WFC saturation level of 84 788 in electrons divided by GAIN 2 0 for WFC1 and WFC2 ST Mag Zeropoint taken from ACS ZP calculator for counts image not cps in this case so calculator STmag value 2 5logvi exposure time so 25 746 2 5l0g 1136 0 SATUR_LEVEL 42356 8 SATUR_KEY SATURATE MAG_ZEROPOINT 33 3787 MAG_GAMMA 4 8 Post SM4 ACS WFC Default Gain Native ACS WFC scale 0 05 arcsec per pixel or you can leave as to automatically use the FITS WCS info as below Only used for CLASS_STAR calculation GAIN 2 0 GAIN_KEY GAIN PIXEL_SCALE 6 05 ee eee SEEING_FWHM 1 2 FWHM for stellar source in ACS WFC image should be 4 pixel and default drizzle pixel scale for ACS WFC is 5arc
16. 56 0 158230 jabu0lgmq_fic fits 0 082594 0 001245 359 998965 1 000009 0 165687 0 163800 jabu0lgsq_flc fits 0 081501 0 004551 359 998707 1 000003 0 139776 0 153342 jabu0lgyq_fic fits 0 169839 0 060228 359 998981 1 000007 0 146863 0 156113 jabu0lhcq_flc fits 0 133796 0 109905 359 999174 1 000007 0 147139 0 157516 We also obtain plots for each of the images being compared to its reference which by default is the first image in the series Examples of the types of plots we obtain for one of the images in the series are shown below in Figures 5 6 and 7 57 0 6099 Vogg plot of 315 315 residuals Residuals for jabully fg fle fits using 315 sources 22 5 15 20 25 35 a Offset in X pixels Figure 5 Typical initial Figure 6 Typical initial Figure 7 Typical initial histogram of offsets vector plot of residuals x y rms pixel residuals Step 5 Iterating in TweakReg As mentioned above one may want to see if any better solutions can be easily obtained and that some cuts to the input object lists in the catalogs may be made using the built in flux or magnitude limit parameters within the TweakReg task itself And as also mentioned above an awk command to trim catalogs and select objects based on greater or lesser stellarity may also be used Early type galaxies ellipticals etc may be better sources to use for alignment because they are less prone to changes in 11 morphological ap
17. COORDINATE FILE DESCRIPTION catfile coords_catfile lis File containing coordinate filenames for input files xcol 1 Column name s for X positions ycol 2 Column name s for Y positions fluxcol 3 Column name for source flux mag values fluxunits mag Units of flux values xyunits pixels Units of X Y positions nbright None Number of brightest objects to keep maxf lux None Maximum flux value for valid objects minf lux None Minimum flux value for valid objects REFERENCE CATALOG DESCRIPTION refcat Filename of reference coordinate catalog refxcol 1 Column name s for RA refycol 2 Column name s for Dec refxyunits pixels Units of sky positions rfluxcol 3 Column name for source flux mag values rf luxunits mag Units of flux values refnbright None Number of brightest reference objects to keep rmaxf lux None Maximum flux value for valid reference objects rminf lux None Minimum flux value for valid reference objects OBJECT MATCHING PARAMETERS minobj 15 Minimum number of objects acceptable for matching searchrad 1 6 The search radius for a match searchunits arcseconds Units for search radius useZdhist True Use 2d histogram to find initial offset seeZdplot True See 2d histogram for initial offset tolerance 1 6 Matching tolerance for xyxymatch pixels separation 6 5 Minimum object separation pixels xoffset 6 6 Initial guess for X offset pixels
18. RAMETERS minobj 15 Minimum number of objects acceptable for matching searchrad 1 6 The search radius for a match searchunits arcseconds Units for search radius use2dhist True Use 2d histogram to find initial offset seeZdplot True See 2d histogram for initial offset tolerance 1 8 Matching tolerance for xyxymatch pixels separation 6 5 Minimum object separation pixels xoffset 6 0 Initial guess for X offset pixels yoffset 6 0 Initial guess for Y offset pixels CATALOG FITTING PARAMETERS fitgeometry rscale Fitting geometry residplot both Plot residuals from fit nelip 3 Number of clipping iterations in fit sigma 3 6 Clipping Limit in sigma units ylimit None Upper Lower limit in pixels for residplot labelsize 8 Font size in points for plot labels 26 Appendix H Ultimate TweakReg Run Parameters _task_name_ tweakreg input flce fits Input files name suffix or list refimage Filename of reference image exclusions Filename for source exclusions catalogs updatewcs False Update WCS keywords of input images writecat True Write out source catalogs clean False Remove intermediate files verbose False Print extra messages during processing runfile tweakreg log Filename of processing log expand_refcat False Expand reference catalog with new sources enforce_user_order True Align images in user specified order interactive True A
19. True Create CR cleaned _crclean file and a _crmask file driz_cr_snr 3 5 3 6 Driz_cr SNR parameter driz_cr_grow 1 Driz_cr_grow parameter driz_cr_ctegrow Driz_cr_ctegrow parameter driz_cr_scale 1 2 4 7 Driz_cr scale parameter STEP 7 DRIZZLE FINAL COMBINED IMAGE driz_combine True Perform final drizzle image combination final_wht_type IVM Type of weighting for final drizzle final_kernel square Shape of kernel function final_wt_scl exptime Weighting factor for input data image final_pixfrac 1 6 Linear size of drop in input pixels final_fillval None Yalue to be assigned to undefined output points final_bits 6 Integer mask bit values considered good final_units cps Units for final drizzle image counts or cps STEP 7a CUSTOM WCS FOR FINAL OUTPUT final_wes False Define custom WCS for final output image final_refimage Reference image from which to obtain a WCS final_rot None Position Angle of drizzled image s Y axis w r t North degrees final_scale None Absolute size of output pixels in arcsec pixel final_outnx None Size of FINAL output frame X axis pixels final_outny None Size of FINAL output frame Y axis pixels final_ra None right ascension output frame center in decimal degrees final_dec None declination output frame center in decimal degrees INSTRUMENT PARAMETERS gain gnkeyword rdnoise rnkeyword exptime
20. a were taken within the same visit At that point we will 6 re run the TweakReg task for the images in each same filter same visit set this time updating the header information with the solution required to align all the images in a given filter for that visit Although perhaps not fully covered in this example since there are other examples regarding this in typical usage and situations the resulting per filter aligned images can then be 7 drizzled together again and the drizzled output used as a reference image to be fed to the DrizzlePac TweakBack task to update the headers of all the images in all of the filters to that reference image after which they can all be drizzled together on a per filter basis with the resulting output also being aligned across both all visits and all filters We will show examples of task parameter files of SExtractor set up files input settings and their content of the various output catalogs and their content and format and show some possibly helpful means of manipulation of the output catalogs etc as well as giving some advice as to other things one may try in order to make the solution better since this paper is merely describing a general approach and not detailing all of the possibilities Step 1 Update the WCS Information for Geometric Distortion This first step will only be required to be done manually until late 2015 when this part of the process is to be incorporated into the routine pip
21. al values to see if any improvement is readily possible Recommendations In situations such as we have described where SExtractor is needed we recommend the creation of cosmic ray cleaned images as input for SExtractor We recommend the use of SExtractor version 2 8 6 or later In SExtractor s default sex file the back_size should be a little larger than an average typical small faint galaxy in number of pixels A value of 64 is a good value for small HUDF like galaxies together with a back_filtersize of 3 or so A detect_minarea of 3 and detect_thresh of 7 are similarly reasonable values and analysis_thresh can sometimes also be useful for experimentation Cuts in the lists based on magnitude x y position stellarity and several other edits may help make the solution better but ultimately the use of inverse variance weight maps is one of the best aids to better solutions Acknowledgements We are grateful to Mihai Cara Warren Hack and fellow members of the STScI DrizzlePac AstroDrizzle Working Group for advice and a careful reading of this paper References SExtractor SExtractor http www astromatic net software sextractor Bertin E amp Arnouts S 1996 SExtractor Software for Source Extraction Astronomy amp Astrophysics Supplement 317 393 Bertin E SExtractor v2 13 User s Manual at https www astromatic net pubsvn software sextractor trunk doc sextractor pdf Akhlaghi M 2012 Notes on SExtractor
22. atalogs basic manipulation of those catalogs and their use with the TweakReg task in the DrizzlePac package More options are explored for iteratively improving the astrometric solution than in Paper I ACS ISR 2015 04 but this still represents an intermediate level of sophistication in methods This paper introduces several methods but the ultimate best methods can vary with the nature of the objects and the data etc and are for the user to explore Also the use of crclean fits images may be more suited to ACS WFC and WFC3 UVIS than WFC3 IR Introduction Although the stellar oriented built in object detection routine ImageFindPars in DrizzlePac s TweakReg task can be quite useful for aligning images in most fields which have plenty of stars for alignment there are some situations in which there are not many or any stars in the images to be aligned and in which even those few stars may have moved due to proper motion if the images were taken over a long enough time baseline such as archival data from different observing programs on the same target separated by some number of years Additionally morphological differences in multiwavelength sets of images of galaxies may even make some galaxies less suitable than others as reference objects for registration and alignment In this example we are addressing the simplest case merely using SExtractor software to generate very simple external catalogs to feed to the TweakReg task for alignme
23. atalogs which was set by what we have defined in our default params file the awk syntax for trimming objects in a 100 pixel border around the edges of the ACS WFC chips which are 4096 x 2048 pixels each would be this NOTE The line below wraps 12 awk 1 amp amp 1 gt 100 amp amp 1 lt 3996 amp amp 2 gt 100 amp amp 2 lt 1948 jabu01fvq_crclean_ext1 cat gt jabu01fvgq_crclean_trimv1_ext1 cat The 1 represents the column of x values and 2 the column of y values From this example one may also anticipate part of the command necessary to trim the list based on stellarity etc except for which stellarity values to use as a cut off Whether we trimmed our input catalog object lists by magnitude ranges or by trimming some portion of a border area around the chip edges or by stellarity or manually by some other means and based on some other criteria to use the trimmed object catalogs in TweakReg the resulting new catalogs must then be referenced in the TweakReg catfile parameter in a new file like the coords_catfile lis which was used for the original TweakReg run We could contineu to call it coords_catfile lis or any other name we wish but to most accurately describe it we ll call it coordstrimmed_catfile lis and it has the same format as the original coords_catfile lis but references the new trimmed catalogs instead as below NOTE The lines below wrap making a total of 6 lines jabu01fvq_filc fits jabu01fvq_c
24. bered that brighter magnitudes correspond to smaller numbers and fainter magnitudes correspond to larger numbers so that when using magnitudes as input in the catalog files the software is written and works such that you must use what seems to be a reverse order for maximum and minimum corresponding to the size of the number rather than the magnitude of the source For example when using magnitudes rather than regular flux measurements you would specify maxflux 24 0 and minflux 20 0 to select and trim the magnitude range to include only sources from magnitude 20 0 to 24 0 in your input SExtractor catalog for use in matching sources although the name of the parameters make that seem counterintuitive and to prefer the opposite One will encounter crashes with errors if using the values for these parameters in the same sense for magnitudes as for regular fluxes Another kind of object filtering one may want to do is to trim the objects around the edge of the chips if they happen to be very close to the edge or suspect in those areas for some other reason This may be useful if there are areas in the _crclean fits images which did not have overlap with other images and there are areas around edges which were not effectively cleaned of cosmic rays and those have dominated the object lists there or if there are other spurious or questionable objects detected along the edges of an image For example given the specific format of our output SExtractor c
25. by GAIN 2 8 for WFC1 and WFC2 SATUR_LEVEL 42350 6 level in ADUs at which arises saturation SATUR_KEY SATURATE keyword for saturation level in ADUs ST Mag Zeropoint taken from ACS ZP calculator for counts image not cps in this case so calculator STmag value 2 5logvi exposure time so 25 746 2 5l0g 1138 80 MAG_ZEROPOINT 33 3787 magnitude zero point 5 3 5 3 5 MAG_GAMMA 4 0 gamma of emulsion for photographic scans Post SM4 ACS WFC Default Gain is 2 0 For Pre SM ACS WFC data the default was Gain 1 GAIN 2 0 detector gain in e ADU GAIN_KEY GAIN keyword for detector gain in e ADU Native ACS WFC scale 0 05 arcsec per pixel or you can leave as to automatically use the FITS WCS info as below Only used for CLASS_STAR calculation PIXEL_SCALE 6 05 size of pixel in arcsec G use FITS WCS info Star Galaxy Separation S5EEING_FWHM 1 2 stellar FWHM in arcsec FWHM for stellar source in ACS WFC image should be 1 pixel and default drizzle pixel scale for ACS WFC is 5arcsec pixel Can allow a bit so try 0 08 SEEING_FWHM 6 88 stellar FWHM in arcsec Only used for CLASS_STAR calculation STARNNW_NAME default nnw Neural Network_Weight table filename Back_size should be a little larger than your average typical small faint galaxy in number of pixels BACK_SIZE 64 Background mesh lt size gt or lt width gt lt height gt
26. clip 5 Number of clipping iterations skylsigma 4 6 Lower side clipping factor cin sigma skyusigma 4 0 Upper side clipping factor fin sigma skyuser KEYWORD indicating a sky subtraction value if done by user skyfile Name of file with user computed sky values skymethod localmin Sky computation method skymask_cat Catalog file listing image masks use_static True Use static mask for skymatch computations sky_bits 6 Integer mask bit values considered good pixels in DQ array STEP 3 DRIZZLE SEPARATE IMAGES driz_separate True Drizzle onto separate output images driz_sep_kernel turbo Shape of kernel function driz_sep_wt_scl exptime Weighting factor for input data image driz_sep_pixfrac 1 6 Linear size of drop in input pixels driz_sep_fillval None Value to be assigned to undefined output points driz_sep_bits Integer mask bit values considered good driz_sep_compress False Use compression when writing out product STEP 3a CUSTOM WCS FOR SEPARATE OUTPUTS driz_sep_wes False Define custom WCS for separate output images driz_sep_refimage Reference image from which to obtain a WCS driz_sep_rot None Position Angle of drizzled image s Y axis w r t North degrees driz_sep_scale None Absolute size of output pixels in arcsec pixel driz_sep_outnx None Size of separate output frame s X axis pixels driz_sep_outny None Size of separate output frame
27. e and the original SExtractor output catalog overplotted in green Figure 2 Extension 4 of one of the images above and the original SExtractor output catalog overplotted in green Figure 3 Close up above showing detail of some of the SExtractor catalog objects including some in the lensed arc Some spurious objects are visible in the lensed arc in Extension 1 and in the bright star in Extension 4 However most catalog object entries look real and reasonable when looking at the objects in the images on which they are overplotted Such sanity checks are always important to make and can also help inform choices of objects to delete in an attempt to find a better solution when doing iterative TweakReg runs Figure 4 Close up above showing detail of some of the SExtractor catalog objects including some which are artifacts associated with the bright star Step 4 Feed SExtractor Catalogs to TweakReg Once you have created the SExtractor catalogs on the basis above a separate catalog for each chip of each image you can then feed them to the TweakReg task in order for it to do its source matching and alignment It is usually an iterative process so you will usually run TweakReg multiple times with the updatehdr keyword set to False No during those iterations and only set it to True Yes in a final re run of TweakReg when you have found a solution which you consider acceptable and have set the task
28. ection and measuring parameters and also trimming catalog lists by magnitude limits spatial chip edge limits and stellarity as well as by manual massaging of individual case by case circumstances of various sorts which may help to make a final solution somewhat better it is generally the case that the most effective way to make the coordinate measures of objects the most reliable and consistent in SExtractor and improve the solutions by a significant amount is to incorporate the use of the relevant weight map always in IVM format as required by SExtractor when detecting and measuring the positions of objects The use of a weight map can easily be specified on the command line when running SExtractor It can potentially be very helpful in almost all circumstances but perhaps especially so in cases such as when measuring objects taken across different visits and in mosaics or stacks where there are areas of varying depth and signal to noise This practice will be addressed in more detail elsewhere including in the Frontier Fields technical documentation and scripts when published Using inverse variance IVM weight maps when available is probably the single most beneficial improvement one can make in obtaining better coordinates and registration Along with that the kinds of things described in this ISR including trimming the list of objects by removing fainter objects extraordinarily bright objects such as bright stars objects on the edges of t
29. eline processing in OPUS 2015 3 Until that time one must download new reference files for the IDCTAB NPOLFILE and D2IMFILE and use the setval task to first update the keyword values for the IDCTAB NPOLFILE and D2IMFILE keywords in the science image headers and then use the task updatewcs to apply the corrections from the new files to the science images Bear in mind that if you update one of these files you should update all three as they are intended for use together as an ensemble Throughout this example it is assumed that the standard pipeline calibrated de striped CTE corrected _flc fits images are being used and those are the ones to which these geometric corrections are being applied This process is currently described in more detail on the ACS Distortion web page at http www stsci edu hst acs analysis distortion and can briefly be summarized thus as taken from the text of that page gt from astropy io import fits gt fits setval image filename IDCTAB value location of IDCfile IDCFILEname fits gt fits setval image filename NPOLFILE value location of NPOLfile NPOLFILEname fits gt fits setval image filename D2IMFILE value location of D2IMfile D2IMFILEname fits gt from stwcs import updatewcs gt updatewcs updatewcs flc fits update the WCS in the header Also as per instructions on that page be sure not to use the updatewes task again as part of your subsequ
30. ent TweakReg and AstroDrizzle runs as you try to find an optimal alignment since re running the updatewcs task will over write any previous corrections you have made with your initial run and subsequent iterations of TweakReg Instead use the updatehdr keyword with value set to False No during your TweakReg iterations and then change it to True Yes when you have found a solution you like and are re running TweakReg for the last time Step 2 Initial AstroDrizzle Run to Make Cosmic Ray Cleaned Images In this and subsequent sections on AstroDrizzle and TweakReg you may run python commands or use the Teal interface to execute the tasks These are described elsewhere and we will merely describe the non default parameter values which have been selected In order to make initial cosmic ray cleaned images to feed to SExtractor we make a separate directory for all the images in a given filter for that visit and place the images for that filter into it Then we make use of the existing WCS information in the science image headers to first combine the images on that same visit same filter basis Since we have 6 images in the same filter per visit we use combine_type iminmed in making the median image and driz_cr_corr True If desired a final drizzled science image though substandard without any better alignment being applied with an associated weight image of type IVM can be created using driz_combine True and
31. er let author Author name for creator of header let descrip Short description of headerlet solution catalog Name of catalog used for headerlet solution history Name of ASCII file containing history for header let OPTIONAL SHIFTFILE OUTPUT shiftfile True Create output shiftfile outshifts shifts ver3 txt Filename of generated shiftfile outwes shifts ver3_wcs fits Filename of shiftfile reference WCS COORDINATE FILE DESCRIPTION catfile coords_catfile lis File containing coordinate filenames for input files xcol 1 Column names for X positions ycol 2 Column name s for Y positions fluxcol 3 Column name for source flux mag values fluxunits mag Units of flux values xyunits pixels Units of X Y positions nbright None Number of brightest objects to keep maxf lux 24 0 Maximum flux value for valid objects minf lux 26 6 Minimum flux value for valid objects REFERENCE CATALOG DESCRIPTION refcat Filename of reference coordinate catalog refxcol 1 Column name s for RA refycol 2 Column name s for Dec refxyunits pixels Units of sky positions rfluxcol 3 Column name for source flux mag values rf luxunits mag Units of flux values refnbright None Number of brightest reference objects to keep rmaxf lux None Maximum flux value for valid reference objects rminf lux None Minimum flux value for valid reference objects OBJECT MATCHING PA
32. he image which may not have been measured as well objects with complex morphologies which may also vary more greatly from bandpass to bandpass although they may be OK internally within a single filter and in the case of images taken over a long time baseline removal of stars which may have proper motion all of these and still more things represent areas which may be investigated tried for possible improvement of the solution All datasets and combinations of datasets are different and each present their own unique challenges Conclusions We have shown examples of parameter files for DrizzlePac s AstroDrizzle and TweakReg tasks as they may be used in preparing cosmic ray cleaned images for the use of SExtractor on them and in incorporating SExtractor produced object catalogs for use in image alignment and registration We have also shown examples of the four basic SExtractor startup files default sex default conv defaul nnw and default params as 15 they might be used on datasets of this sort We have also shown examples of other files such as the SExtractor catalog format and the image plus catalog file lists such as coords_catfile lis needed in the process Finally as an aid to using these tools we have also given advice on some general guidelines for items such as suggested values for some critical parameters and we have given advice on some things to explore in iterative efforts to improve astrometric solutions beyond their initi
33. important thing here is the relative difference in magnitudes between objects within any given system since it is used in TweakReg for setting faint and bright limits on the list of objects to include for matching If the information about FWHM and pixel scale was used such that SExtractor stellarity values are valid then that quantity may also be used to eliminate some objects from the matching solution if desired by the use of awk commands etc Other options for trimming the object lists in the input catalogs include trimming boundaries of some number of pixels in x and y around the edges of the chips also by the use of awk commands An example of this will be shown in the section on Step 5 Iterating in TweakReg It is always a good idea to actually look at some catalogs overplotted on your images to see if they actually seem to be reasonable picking up real objects in a reasonable magnitude range getting reasonable looking centers for them and discriminating well between sources in complex areas with multiple objects etc To do this with the use of awk commands for example on can easily turn a copy of input catalogs into files of ds9 region format and then overplot them on the single chip images Examples of two of our initial catalogs are shown in Figures 1 and 2 representing the 2 different chips of one of the _crclean fits images while Figures 3 and 4 show some of the details Figure 1 Extension 1 of one of the images abov
34. ines the quantities to be output into the catalog from the SExtractor run These input files are automatically called when SExtractor is run Examples of these 4 input files are shown in Apendices B C D and E In our usage here we have used mostly default parameters in the creation of these simple basic catalogs but we have changed a few items which we will highlight We also include some commentary on the parameter values in annotations within the example files To run SExtractor the default files must be in the working directory and set up with parameter values as desired Then bearing in mind the offset in extension number assuming use of SExtractor version 2 8 6 as was used here and specifying as the catalog name and the checkimage name in the default sex file as shown in Appendix B the commands to issue are simply of the form below the two line commands wrap sex catalog_ name jabu0lfvq_crclean_extl cat checkimage_name jabu01fvq_crclean_extl_check fits jabu01fvq_crclean fits 0 sex catalog_ name jabu0lfvq_crclean_ext4 cat checkimage_name jabu01fvq_crclean_ext4_check fits jabu01fvq_crclean fits 3 etc such that a separate catalog and checkimage is generated for each of the two chips for each image since the TweakReg task expects its input in that format You could instead just issue the commands above in the format of sex jabu01fvq_crclean fits 0 if you edited the name of the output catalog
35. ions in frequent use such as version 2 5 0 In SExtractor version 2 5 0 the software will run on multi exension FITS images but it runs on all extensions and it is then necessary to make the extension number one of the outputs and to then filter out the catalogs generated for all other extensions except for the one s desired In contrast in SExtractor version 2 8 6 one may run the software on a single image extension at a time but there is an offset which must be applied Although in SExtractor version 2 5 0 output the image extensions 1 and 4 correctly refer to the two science image extensions of primary concern for measuring and cataloging object positions in SExtractor version 2 8 6 one must refer to those extensions as 0 and 3 respectively when running SExtractor on those two science image extensions When running SExtractor 4 basic set up files are involved 1 default sex which is where parameters for minimum object size background filters detection threshold levels photometric systems and zeropoints seeing_fwhm and pixel_scale both only used for SExtractor s class_star galaxy star discriminator and other similar items fundamental to the objects themselves are defined 2 default conv which applies convolution filters of the user s choice gaussian Mexican hat etc in object detection and characterization 3 default nnw which defines a neural network for object classification and 4 default param which def
36. llow interactive display of plots UPDATE HEADER updatehdr True Update headers of input files with shifts wesname TWEAKF475w Name of updated WCS HEADERLET CREATION headerlet False Create headerlet for solution attach True Create headerlet FITS extension hdrfile Filename for headerlet FITS file clobber False Overwrite existing headerlet FITS file hdrname Unique name HDRNAME for header let author Author name for creator of headerlet descrip Short description of headerlet solution catalog Name of catalog used for headerlet solution history Name of ASCII file containing history for header let OPTIONAL SHIFTFILE OUTPUT shiftfile True Create output shiftfile outshifts shifts ver3 update txt Filename of generated shiftfile outwes shifts ver3 update_wes fits Filename of shiftfile reference WCS COORDINATE FILE DESCRIPTION catfile coords_catfile lis File containing coordinate filenames for input files xcol 1 Column name s for X positions ycol 2 Column name s for Y positions fluxcol 3 Column name for source flux mag values fluxunits mag Units of flux values xyunits pixels Units of X Y positions nbright None Number of brightest objects to keep maxf lux 24 6 Maximum flux value for valid objects mint lux 26 6 Minimum flux value for valid objects REFERENCE CATALOG DESCRIPTION refcat Filename of reference coordina
37. m HST program 11507 PI Noll The data were taken in 2009 not long after SM4 and are comprised of 6 dithered ACS WEC images in each of three filters F475W F625W and F814W A formatted version of the Phase II file may be seen at http www stsci edu hst phase2 public 11507 pro via the standard program information web pages We do not push the limits of everything we could try nor the limit of what could be achieved in this example but we show enough to give an idea of how the solution can be improved Process We will first 1 update the WCS and geometric distortion in each of the images a process specific to ACS WFC which currently has to be done manually but which will be automated as part of the routine pipeline by late 2015 as part of OPUS 2015 3 Next we will 2 make an initial run of AstroDrizzle on the same filter same visit images to generate cosmic ray cleaned images called _crclean fits which will be used in 3 generating the SExtractor catalogs After generating the SExtractor catalogs from the crclean fits images we will 4 feed those catalogs to TweakReg and 5 manipulate the input catalogs if needed desired iterating in each filter internally as needed without updating the headers until we have a solution which we deem more acceptable for each of the images in a given filter and then moving on to the next filter until we have a solution which seems reasonable for each filter Remember that in this case all the dat
38. nt of images SExtractor however needs good clean images to produce better results but images by default usually have many cosmic rays in them which complicate the tasks of object detection position measurement and ultimately image alignment Although new developments with the default ImageFindPars task and TweakReg allow for use of the data quality DQ arrays to ignore or eliminate the use of objects affected by cosmic rays SExtractor does not use the DQ array information hence the need for first making the cr clean fits images In terms of ideal conditions for attacking this problem if such images are available it is always best to start by aligning and combining images from the same visit the same guide star acquisition and in the same filter and then later expanding that to aligning and combining across visits in the same filter and ultimately across both different filters and different visits Therefore in general if designing an observing program it is also a good idea to keep this in mind as an ideal set up for aligning and drizzling images together If you can have multiple images of similar exposure time in the same filter and same visit then do that It may not always be possible but that is a good ideal situation In this example we have taken an even simpler approach where all of the images in all of the filters were taken in one single visit We have used the ACS SM4 ERO images of the galaxy cluster Abell 370 fro
39. o achieve with the current process if it is desired to continue with that alignment the TweakReg task must be run once more with the updatehdr keyword set to Yes in order to apply the corrections to all the _flc fits images in that same filter same visit set Appendix H shows a version of such ultimate TweakReg parameters with the main difference being that one keyword value for updatehdr being set to Yes True Step 7 The Remainder of the Process We will not cover all of the rest of the process in detail here but will merely briefly describe it since it is re integrated with the rest of the process that would normally be used had the input catalogs been those generated internally in TweakReg via the use of the built in ImageFindPars task Once you have internally aligned each same visit same filter combination of images you can then drizzle a set of them in one filter to a final _drc fits image which you can then use as a reference image to transfer the solution to all the _flc fits images across all filters and all visits via the DrizzlePac TweakBack task Those images can then all be 14 drizzled together on a per filter basis with the resulting images all being aligned together This process is described elsewhere in other examples and documentation and will not be described further here The reader is referred to that documentation instead The Best SExtractor Options Although varying SExtractor object det
40. pearance over the wavelength range of images in several filters but stars may also be bad sources to use for alignment if saturated or if spurious sources were found around them in their diffraction spikes or airy rings or other artifacts in the PSF or if they have a high enough proper motion and if images were taken far enough apart in time that the stars have moved between the frames This is not the case here in this example and it is generally only the case when observations are separated by some number of years for the highest proper motion stars in most fields Appendix G represents an example of a TweakReg parameter file from one of the iterations If we manually deleted any objects from the object list it will not contain parameters for that One very important thing to mention regarding automatic trimming of the input catalogs within TweakReg based on flux limits or magnitude limits is the correct usage of the maxflux and minflux parameter values in TweakReg If the catalog values are simply in flux units then maxflux and minflux may be used simply and intuitively just as they would seem to imply In the case of using regular flux measurements a larger number corresponds to a brighter source and a smaller number corresponds to a fainter source However if the SExtractor catalog flux values have been converted into magnitudes as is the case in this example then the use of maxflux and minflux can be a bit counterintuitive It must be remem
41. put files Ray A Lucas 31 May 2812 Re ordering from default Instead of Number I start with these output parameters to order them in the format in which the new Drizzlepac tweakreg task requires them Ray 4 Lucas 2012 05 31 X_IMAGE Y_IMAGE MAG_AUTO CLASS_STAR NUMBER Original below here with duplicate moved items commented out H EXT_NUMBER in SExtractor v2 8 6 all output extension numbers are 1 so useless to specify NUMBER FLUX_ISO FLUXERR_ISO NAG_ISO MAGERR_ISO FLUX_ISOCOR FLUXERR_ISOCOR MAG_ISOCOR MAGERR_ISOCOR FLUX_APER L FLUXERR_APER 1 MAG_APER 4 MAGERR_APER 1 FLUX_AUTO FLUXERR_AUTO MAG_AUTO MAGERR_AUTO FLUX_BEST FLUXERR_BEST MAG_BEST MAGERR_BEST KRON_RADIUS BACKGROUND THRESHOLD MU_THRESHOLD FLUX_MAX MU_MAX ISOAREA_IMAGE ISOAREA_WORLD XMIN_IMAGE YMIN_IMAGE XMAX_IMAGE YMAX_IMAGE X_IMAGE Y_IMAGE _WORLD _WORLD ALPHA_SKY DELTA_SKY ALPHA_J2688 DELTA_J2666 ALPHA_B1956 DELTA_B1958 X2_IMAGE 2_IMAGE XY_IMAGE 82_WORLD 2_WORLD XY_WORLD 23 SExtractor default params file continued PHOT_APERTURES 5 PHOT_AUTOPARAMS 2 PHOT_PETROPARAMS 2 MAG_APER aperture diameter s in pixels MAG_AUTO parameters lt Kron_fact gt lt min_radius gt MAG_PETRO parameters lt Petrosian_fact gt lt min_radius gt This is the average ACS WFC saturation level of 84 700 in electrons divided
42. rclean_trimv1_ext1 cat jabu01fvq_crclean_trimv1_ext4 cat jabu0l gfq_flc fits jabu01 gfq_crclean_trimv1_ext1 cat jabu01lgfq_crclean_trimv1_ext4 cat jabu01lgmq_flc fits jabu01gmq_crclean_trimv1_ext1 cat jabu01lgmq_crclean_trimv1_ext4 cat jabu01gsq_flc fits jabu01lgsq_crclean_trimv1_ext1 cat jabu01gsq_crclean_trimv1_ext4 cat jabu0l gyq_flc fits jabu0lgyq_crclean_trimv1_ext1 cat jabu0lgyq_crclean_trimv1_ext4 cat jabu0lhcq_flc fits jabu0 lheq_crclean_trimv1_ext1 cat jabu0lhcq_crclean_trimv1_ext4 cat It should also be remembered that although automation of object inclusion or exclusion in the source lists is generally most desirable if need be the input object lists can even be manually edited to include or exclude any particularly useful or troublesome objects as the case may be Quoting from Paper I ACS ISR 2015 04 You may also want to try deleting from your catalogs troublesome objects which have high residuals as shown in the TweakReg plots but that too can be tricky and the size of an object s residuals may vary some from image to image and catalog to catalog In general it is perhaps better to use other methods such as scripted awk commands to remove such objects on the periphery or elsewhere or within specified magnitude ranges or stellarity 13 values or ellipticity or galaxy morphology type etc Small elliptical galaxies may be better than galaxies with more complex morphology when having to compare across different
43. s Y axis pixels driz_sep_ra None right ascension output frame center in decimal degrees driz_sep_dec None declination output frame center in decimal degrees STEP 4 CREATE MEDIAN IMAGE median True Create a median image median_newmasks True Create new masks when doing the median combine_maskpt 6 3 Percentage of weight image value below which it is flagged as a bad pixel combine_type iminmed Type of combine operation combine_nsigma 4 3 Significance for accepting minimum instead of median combine_nlow minmax Number of low pixels to reject combine_nhigh minmax Number of high pixels to reject combine_lthresh None Lower threshold for clipping input pixel values combine_hthresh None Upper threshold for clipping input pixel values combine_grow 1 Radius pixels for neighbor rejection combine_bufsize None Size of buffer in Mb for each input image 18 Initial AstroDrizzle Input Parmeters continued STEP 5 BLOT BACK THE MEDIAN IMAGE blot True Blot the median back to the input frame blot_interp poly5 Interpolant nearest linear poly3 poly5 sinc blot_sinscl 1 6 Scale for sinc interpolation kernel blot_addsky True Add sky using MDRIZSKY value from header blot_skyval 8 6 Custom sky value to be added to blot image STEP 6 REMOVE COSMIC RAYS WITH DERIV DRIZ_CR driz_cr True Perform CR rejection with deriv and driz_cr driz_cr_corr
44. sec pixel Can allow a bit so try 0 08 SEEING_FWHM STARNNW_NAME 6 08 default nnw level in ADUs at which arises saturation keyword for saturation level in ADUs magnitude zero point gamma of emulsion for photographic scans is 2 0 For Pre 5M4 ACS WFC data the default was Gain 1 detector gain in e ADU keyword for detector gain in e ADU size of pixel in arcsec Bsuse FITS WCS info stellar FWHM in arcsec stellar FWHM in arcsec Only used for CLASS_STAR calculation Neural Network_Weight table filename Back_size should be a little larger than your average typical small faint galaxy in number of pixels BACK_SIZE 64 BACK_FILTERSIZE 3 BACKPHOTO_TYPE GLOBAL CHECKIMAGE_TYPE OBJECTS Give this in the command Line CHECKIMAGE_NAME jabu ifvq_crclean_ext1_check fits CHECK IMAGE_NAME fe eae MEMORY_OBISTACK 3888 MEMORY_PIXSTACK 308088 MEMORY_BUFSIZE 1024 a aa a eae VERBOSE_TYPE NORMAL WRITE_XML N XML_NAME sex xml NTHREADS 6 Background mesh lt size gt or lt width gt lt height gt Background filter lt size gt or lt width gt lt height gt can be GLOBAL or LOCAL Check Image can be NONE BACKGROUND BACKGROUND_RMS MINIBACKGROUND MINIBACK_RMS BACKGROUND FILTERED OBJECTS OBJECTS SEGMENTATION or APERTURES instead Filename for the check image Filename for the check image number of objects in stack
45. te catalog refxcol 1 Column name s for RA refycol 2 Column name s for Dec refxyunits pixels Units of sky positions rfluxcol 3 Column name for source flux mag values rf luxunits mag Units of flux values refnbright None Number of brightest reference objects to keep rmaxf lux None Maximum flux value for valid reference objects rminf lux None Minimum flux value for valid reference objects OBJECT MATCHING PARAMETERS minobj 15 Minimum number of objects acceptable for matching searchrad 1 6 The search radius for a match searchunits arcseconds Units for search radius use2dhist True Use 2d histogram to find initial offset seeZdplot True See 2d histogram for initial offset tolerance 1 4 Matching tolerance for xyxymatch pixels separation 6 5 Minimum object separation pixels xoffset 6 6 Initial guess for X offset pixels yoffset 6 0 Initial guess for Y offset pixels CATALOG FITTING PARAMETERS fitgeometry rscale Fitting geometry residplot both Plot residuals from fit nelip 3 Number of clipping iterations in fit sigma 3 6 Clipping Limit in sigma units ylimit None Upper Lower limit in pixels for residplot labelsize 8 Font size in points for plot labels 27
46. then iterate further if we feel it is needed or just to see if we can easily improve on the initial solution Our initial run task parameters for TweakReg are shown in Appendix F Note that though we don t use it directly just for our own informational purposes we produce a differently named by version number and other distinguishing characteristics etc shift file and wcs fits file for each tentative run even though we are not updating the header with any improved solutions at this stage This allows us to get a better sense of how consistently different iterations are finding very nearly the same shifts or where they may deviate more significantly and to see the x and y rms values for each image in that run to which we can refer along with the plots for each run which we also save for comparison naming 10 them by the most distinguishing part of their rootname and iteration or version number and any other particular differences we made in the input catalogs etc An example of the shift file we obtain from our initial run is here below From left to right the quantities reported are image x shift y shift rotation scale x rms and y rms x and y shifts and rms units are in pixels rotation is in degrees frame output refimage shifts verl_wes fits wcs form delta units pixels jabu0lfvq_flc fits 0 000000 0 000000 0 000000 1 000000 0 000000 0 000000 jabu0lgfq_fic fits 0 022882 0 024646 359 999418 1 000002 0 1600
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