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aXeSIM User Manual (pdf download, 1.0Mb)

1. in a two column ASCII or fits format plus Model Object Table From the Model Object Table the task uses only the redshift and a magnitude column to shift the template spectra in redshift and flux The output is a multi dimension fits table Every extension represents a template spectrum shifted to a certain redshift and scaled to some flux value specified in the corresponding row of the input table Usage prepspectra inlist incat tpass flux 38 CHAPTER 4 THE AXESIM TASKS Parameters inlist mandatory string The name of the Spectrum Template List The template spectra therein can have ASCII or fits format incat mandatory string The Model Object Table with the magnitude values and redshift values to shift the template spectra in flux and redshift tpass_flux mandatory string Total passband to be used for the scaling of the template spectra in the flux space This is either an ASCII or fits file name or an expression of the form lambda_min lambda_max nm In the latter case the passband has a boxcar shape with lambda_min and lambda_max as boundaries model_spectra optional string Name of the output multi extension fits table to store the shifted template spectra Input and Output Input e AXE_IMAGE PATH incat e AXE SIMDATA PATH content of inlist tpass flux e inlist Output e AXE OUTSIM PATH all output 4 3 3 SIMDIRIM Description This task generates a simulated dire
2. aXeSIM To configure and then compile the C tasks do the following gt cd taxe iraf ccc gt configure For MacsOSX the option build powerpc must be added to the configure command for Power PC machines and the option build i386 pc macosx for Intel Macs If some libraries used by aXeSIM are not installed in the usual places online parameters must be used to tell the configure script where to find them For example configure with cfitsio prefix your_axelibs cfitsio with gsl prefix your axelibs gsl 1 0 with wcstools prefix your axelibs wcstools 3 0 4 specifies explicitly the location of the GSL and the CFITSIO library Follow the instructions given by the configure script to solve problems The configure script generates a Makefile which is used to compile the aXeSIM binaries Type gt to execute the Makefile and create the binaries The tasks must be installed in the bin sub directory of the aXeSIM iraf directory Simply execute gt make install to move the binaries to their proper location 2 4 aXeSIM Support The aXeSIM sofware package was developed by a dedicated group at the Space Telescope European Coordinating Facility STECF STECF will be support ing the use of the aXe software and the slitless spectroscopic modes of ACS and WFC3 until late 2010 Until that time you can request further help and infor mation via email to stdesk eso org After that time support will be provided
3. by STScI via email to help stsci edu 16 CHAPTER 2 INSTALLING AXESIM Chapter 3 Illustrated aXeSIM examples In this chapter we show some examples for aXeSIM simulations In a step by step approach we present the simulation input the aXeSIM task executed and display the simulation results In order to illustrate all possibilities of aXeSIM we start with very simple examples and finish with rather complex simulations that expose all options in aXeSIM Working with aXeSIM frequently requires modifying or creating ASCII tables in the SEXtractor catalogue format The python module AstroAsciiData dis tributed at http www stecf org software PYTHONtools astroasciidata is very convenient to do this interactively or within small python scripts 3 1 Example 1 Simulation details instrument WFC3 IR G102 of objects 1 object spectrum defined by one magnitude value object brightness defined by one magnitude value flux normalization not required object shape Gaussian default extraction YES Directories and files before the simulation example_1 gt 1s R CONF DATA OUTPUT OUTSIM wfc3_abscal_IRg102_Oth_sens fits wfc3_abscal_IRg102_2nd_sens fits Wfc3 abscal IRgi02 1st sens fits WFC3 IR G102 TV2_sim conf example_1_MOT dat OUTPUT OUTSIM example_1 gt setenv AXE_IMAGE_PATH DATA 17 18 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES 19 5mag 11248nm 1 107 10 erg cm s AA examp
4. columns NUMBER the object identifier int X_IMAGE the x position of the object pix float Y_IMAGE the y position of the object pix float A_IMAGE the major axis rms pix float the minor axis rms pix float THETA_IMAGE the position angle of the major axis deg float MAG_ lt number gt the AB magnitude at the wavelength float lt number gt nm In addition the user has the opportunity to perform more detailed simula tions by e g using high resolution spectral templates at different redshifts and flux levels image templates or total passband curves For more detailed simulations the object list needs additional columns such as SPECTEMP the index of the model spectrum to use int MODIMAGE the index of the image template to use int Z redshift of the object float The columns SPECTEMP and MODIMAGE refer to the spectral templates and image templates to be used in the simulation respectively As a first step the template is translated to the redshift given in the column Z 1 3 The output of aXeSIM The output of the aXeSIM simulation task will always consist of a simulated 2D slitless dispersed image with the spectra of the simulated objects For grism images the simulations can include several dispersed orders If provided with a proper total passband of a filter aXeSIM will also produce the direct image associated to the slitless image The total passband curve con
5. of the aXe manual e derive sensitivity files for all spectral orders e derive total passband files see Sect 5 3 for the direct image filters for simulating direct images see below e specify the collecting area of the telescope with the keyword TELAREA in the configuration file for simulating direct images see below The sensitivity files for the spectral orders must implicitly include the tele scope size For flux scaling spectral templates to a given AB magnitude aXeSIM needs only relative throughputs In case that the total passbands for the fil ters are not available standard passband files for e g the Johnson or Kron Cousins photometric system can be used For simulations of direct images however the total passband of the filter and the collecting area of the telescope must be known The aXeSIM default if not specified in the configuration file for the collecting area is the HST mirror size 45238 93cm calculated from its diameter For HST the shading by the secondary mirror is included in the throughput of the mirrors which is an input for computing the total passbands of the filters 1 6 The PyRAF module Similar to the aXe extraction package 2 available in PyRAF under stsdas slitless axe the aXeSIM package for PyRAF has three layers e at the bottom layer executables compiled from C programs provide the fast processing speed necessary for computing the pixel values in the sim ulated im
6. red solid line the extracted spectrum The green point marks the wave length and normalization flux value the black bar indicates the wavelength interval used for the flux normalization Some annotations e Since exposure time values were specified for the slitless and the direct image these images contain noise according to a simple noise model which takes into account photon noise from sources and sky background and readout noise given in the configuration file In addition this noise model is used to generate the error extension of the slitless and direct images The noise is clearly visible in the background of Fig 3 4 and the continuum of the extracted spectra in Fig 3 5 e Background levels specified in the simdata parameters bck_flux_disp and bck flux disp are added to the simulated images However the default spectral extraction is done on a temporary slitless image that had the background removed Hence the default extraction in aXeSIM is always perfect concerning the sky background removal e When executing the task simdata with a long list of parameters as in this example it is good practice not enter the command line directly but to work with a small PyRAF or cl script that contains the entire command e Due to the narrow passband chosen for flux normalization the continuum 28 CHAPTER 3 ILLUSTRATED EXAMPLES levels of the simulated objects vary significantly At the redshift of object 4 the average
7. s silent optional boolean default yes The silent mode reduces the output written to the screen Input an Output Input e AXE IMAGE PATH incat model spectra model images 40 CHAPTER 4 THE AXESIM TASKS e AXE_CONFIG_PATH config bck_flux if image e AXE_SIMDATA_PATH tpass_direct Output e AXE_OUTSIM PATH all output 4 3 4 SIMDISPIM Description The task generates a simulated dispersed image The objects to be simulated are given in a Model Object Table The Model Object Table may contain references to extensions in a Model Spectra file and Model Image file to be used for specific objects It is possible to add Poisson noise from sources background and readout The final output image will be in units of e s Usage simdispim incat config Parameters incat mandatory string The filename of the Model Object Table with the source list to be simulated config mandatory string The name of the aXe configuration file to be used in the simulations dispim_name optional string The name of the simulated dispersed image created by this task If not given a filename is derived from the name of the Model Object Table lambda_psf optional float The wavelength where the object extent A_IMAGE and B_IMAGE was determined model_spectra optional string The multi extension fits table with the input spectra to be used in the simulations model_images optional string The multi extensi
8. 78908 01 6 500 0 120 0 1 5 1 5 90 0 20 0 0 7 1 O 1 500000 00 1 500000 00 9 000000 01 5 320396 01 2 778888 01 7 650 0 105 0 2 5 1 5 0 0 21 5 0 0 o 0 2 500000 00 1 500000 00 0 000000 00 5 320272e 01 2 779064e 01 8 350 0 150 0 1 5 1 0 90 0 21 5 0 0 0 o O 1 500000 00 1 000000 00 9 000000 01 5 320500e 01 2 778701 01 9 550 0 220 0 1 5 1 5 10 0 21 5 0 0 0 o O 1 500000e 00 1 500000e 00 1 000000e 01 5 320217e 01 2 778866e 01 10 50 0 105 0 1 5 1 5 135 0 21 5 0 0 0 0 1 500000 00 1 500000 00 1 350000 02 5 320847e 01 2 778407 01 11 510 0 140 0 1 5 1 5 90 0 20 0 2 0 9 1 1 500000 00 1 500000 00 9 000000e 01 5 320360 01 2 778884 01 12 490 0 160 0 1 5 1 5 90 0 20 0 5 2 1 1 4 1 500000 00 1 500000 00 9 000000 01 5 320353e 01 2 778846e 01 13 570 0 177 0 1 5 1 5 90 0 20 0 4 1 3 0 5 1 500000 00 1 500000 00 9 000000 01 5 320254 01 2 778921 01 14 400 0 212 0 1 5 1 5 90 0 20 0 1 456 1 6 1 500000 00 1 500000 00 9 000000 01 5 320371 01 2 778707 01 The Image Template List template images lis gt more template_images lis WFC3_IR_1400nm_big_psf fits WFC3_IR_1400nm_psf fits WFC3_IR_950nm_big_psf fits WFC3_IR_950nm_psf fits WFC3_UVIS_350nm_psf fits The Spectrum Template List template_spectra lis gt more template_spectra lis Mann S0 dat starbi template fits starb2 template fits starb3 template fits Mann E dat The simulation command gt simdata incat example_4_MOT
9. 8 flatfield 10 flux normalization 25 format 9 45 GSL 15 High Level Task 33 HST 7 image template list 43 installation 13 IRAF 8 Linux 14 login file 14 Low Level Task 36 model images 44 Model Object Table 8 45 model spectra 44 NICMOS 10 NIMCOS 7 noise 10 online parameter 15 preamble 5 PREPIMAGES 37 PREPSPECTRA 37 PyRAF 8 13 27 python 13 saturation 10 sensitivity file 8 sensitivity variations 10 SExtractor 9 45 SExtractor format 45 SIMDATA 33 SIMDIRIM 38 SIMDISPIM 40 spectral extrapolation 19 spectral interpolation 19 spectrum template list 43 ST ECF 8 STScI 8 STSDAS 13 support 5 15 template image 44 template spectrum 44 total passband 43 50 INDEX WCS 15 WFC3 10 51
10. ATH the path where the aXe configuration file and the sen sitivity file s are located AXE OUTPUT PATH the directory path to which all embedded aXe tasks write their output to This is only intermediate data and can be deleted once the corresponding simlation has finished 47 48 CHAPTER 6 ENVIRONMENTAL VARIABLES Bibliography Kiimmel M Walsh J R Pirzkal N Kuntschner H amp Pasquali A J 2009 PASP 121 The aXe extraction software http www stecf org software slitless_software axe aXe configuration and calibration files http www stecf org instruments ACSgrism calibration http www stecf org instruments WFC3grism The aXe User Manual http www stecf org instruments ACSgrism axe manual html index html Kuemmel M Larsen 5 5 amp Walsh J R 2005 New Developments in aXe ST ECF Newsletter 38 8 http www spacetelescope org about further_information newsletters html newsletter_38 html The stsci_python package http www stsci edu resources software_hardware pyraf stsci_python Thompson R I Illingworth G Bouwens R et al 2005 ApJ 130 1 49 Index ACS 7 10 AXE_CONFIG_PATH 47 AXE IMAGE PATH 47 AXE OUTPUT PATH 47 AXE OUTSIM PATH 47 AXE SIMDATA PATH 47 aXeSIM 8 background 10 27 blooming 10 calibration file 8 CFITSIO 15 compilation 13 configuration file 8 19 dark current 10 direct image 7 9 19 environmental variables 47 equivalent width 36 ETC
11. GE 500 0 100 500 120 500 140 500 160 500 180 500 200 dt dob db db d Gb GR db Gb vonourune 90 90 90 90 90 90 20 20 20 20 20 20 oooooo m nananana anna ooo o 00000 w w www HRHOOO nvrwoxa The Image Template List template images lis gt more template_images lis WFC3 IR 1400nm big psf fits WFC3 IR 1400nm psf fits WFC3 IR 950nm big psf fits WFC3 IR 950nm psf fits WFC3_UVIS_350nm_psf fits The Spectrum Template List template_spectra lis more template_spectra lis s0 template fits starbi template fits starb2 template fits starb3 template fits 3 3 EXAMPLE 3 The simulation command gt simdata incat example_3_MOT dat config WFC3 IR G102 TV2_sim conf utput_root StarBurst inlist spec template spectra lis tpass_flux 1040 1060 inlist ima template images lis exptime disp 2000 0 bck_flux_disp 1 0 tpass_direct wfc3_ir_f110w_tpass_m01 dat exptime dir 100 0 bck flux dir 0 5 Directories and files after the simulation gt le R CONF DATA OUTPUT OUTSIM SIMDATA template_images lis template_spectra lis CONF wfc3_abscal_IRg102_Oth_sens fits WFC3 IR G102 TV2_sim conf Wfc3 abscal IRgi102 1st sens fits WFC3 IR G102 TV2_sim conf simul Wfc3 abscal IRg102 2nd sens fits DATA example 3 MOT dat StarBurst images fits StarBurst spectra fits OUTPUT OUTSIM StarBurst_direct fits St
12. Image 2929s RR REX Ryo 44 50 Model Mages 29299 ommo RR AAA 44 sr Model Spes uox ues ate eke EU Rer x OP AO 44 5 8 Model Object Table sse m ERR m A 45 6 Environmental variables 47 Preamble The Space Telescope European Coordinating Facility STECF is responsible for supporting the slitless spectroscopic modes of the Hubble instruments ACS and WFC3 until late 2010 with stdesk eso org as the main contact address After that time all support simulation and extraction software calibration and user support will be provided by STScI Space Telescope Science Institute STScI with help stsci edu as the central contact The slitless spectroscopy URL s provided in this manual all point to www stecf org and below and this web site will be kept up to date until late 2010 Starting in 2011 the webpages for slitless spectroscopy will be hosted at http www stsci edu resources software_hardware stsdas axe Pages at www stecf org will reflect this and then point to the corresponding location at www stsci edu CONTENTS Chapter 1 Description As part of the ST ECF support for the spectroscopic modes of Wide Field Cam era 3 WFC3 the slitless spectroscopy group of the ST ECF has developed a dedicated simulation package applicable to WFC3 Whilst the package was ini tiated for exploitation of WFC3 slitless grism modes it is equally applicable to other slitless spectroscopy modes of the Hubble Space Telescope HST such a
13. PTION WFC G800L HRC G800L HRC PR200L SBC PR130L SBC PR110 In cluding these slitless modes simply requires including the necessary configura tion files specifying the instrument specific aspects of the slitless spectra these files are already available from the ST ECF web http www stecf org instruments ACSgrism calibration The simulation package also finds application to analysis of existing slitless spectroscopy datasets The simulations can be extracted identically to slitless spectral data allowing quantitative assessment of detected spectra and spec tral features such as emission lines Tasks such as matching spectra against templates convolved with the actual object size and at the grism spectral reso lution determining the detection limits for spectra of given types and measuring cross contamination between spectra are readily achieved More extensive stud ies such as assessing completeness limits of survey observations for a variety of object classes can also be performed aXeSIM is made available in two ways It is distributed via the ST ECF homepage as a PyRAF IRAF module and is made available via a web interface Though based on identical software the web interface targets new less experi enced or occasional users and offers a subset of the options existing in aXeSIM In addition to the software we will also provide from our webpages the nec essary configuration and sensitivity files to run aXeSIM at http ww
14. The aXe SIMulation package aXeSIM User manual version 1 4 M Kummel and J R Walsh H Kuntschner July Ist 2010 Contents 1 Description 11 Dessen ee ae 1 2 User provided input for the PyRAF module 1 3 The output of eXeSIM cc ccc ee eee c ee ed 14 Limitations of aXeSIM 15 General use of aXeSIM 1 6 The PyRAF module 2 Installing aXeSIM 2 1 Begmiremenis ww na een 2 2 Installing from the aXeSIM source distribution 2 3 Compiling the Code nassen ror Rmo 24 aXeSIM S DDORb cas komm omo n eee ERR 3 Illustrated aXeSIM examples SL xcd hbo eee ee it 24 6 we ee Me an BOER oe ES 33 Example 6 0 2 4 500886 bee b koh x x eov m ee bee ds 44 A E E E EE E E E E 4 The aXeSIM tasks 4 1 High Level Tasks Low Level Tasks 4 2 Meb Level Tasks 2 utet n AGA koe eh Banned AA 43 Low Level Tasks y ae ww 431 PREPIMAGES 2 re a 432 PREPSPECTRA 24 000 28 28 Rd 33 9 434 SIMDISPIM ssc hoa eA Saw Ree EE 5 File Formats 5 1 Image Template List Kae era 5 2 Spectrum Template List e Total Passband File o sac cioe teata dnega he be 4 CONTENTS 54 Template Spectrum occa cresta Roe RR I ERE Gem RR 44 5 9 Template
15. ages Most of this code does already exist as part of the aXe extraction package in quantitative contamination see 5 This guaran tees the symmetry between the simulations and the extractions Moreover this legacy code has been used for some years and therefore has proven to be without major bugs or problems e a middle layer with python scripts connects the various C executables and performs less computationally expensive preparatory work e a very thin upper layer makes the python scripts accessible from within PyRAF 12 CHAPTER 1 DESCRIPTION This concept is currently followed in all software published in the stsci_python package 6 Chapter 2 Installing aXeSIM 2 1 Requirements The following are required to run aXeSIM e STSDAS 3 11 or later http www stsci edu resources software_hardware stsdas e PyRAF 1 8 or later http www stsci edu resources software_hardware pyraf 2 2 Installing from the aXeSIM source distribu tion After downloading the aXeSIM 1 4 tarball from http www stecf org software slitless_software axesim move it to the instal lation directory your aXeSIM path and unpack it there with gt gunzip taxe21 taxesimi4 src tar gz gt tar xvf taxe21 taxesimi4 src tar aXeSIM consists of a part written in ANSI C and a second part written in Python www python org For several operating systems statically linked binaries are available at http www stecf org software slitless_software ax
16. al structure of the template image is clearly visi ble in Figure 3 2 which shows the direct image and the dispersed image on the left and right side respectively In total the results comprise e the simulated slitless image example 2 MOT slitless fits the simulated direct image example 2 MOT direct fits the extracted 1D spectrum example 1 MOT slitless 2 SPC fits the 2D grism stamp image file example 1 MOT slitless 2 STP fits the Model Images template images fits The Model Images template images fits is a multi extension fits image which contains all template images listed in template images lis and repli cates user input aXeSIM needs the template images in this compact form and generates this file hence it is considered as part of the result Figure 3 3 shows a comparison of the input spectrum and the default ex tracted spectrum in the left panel and the image template in the right panel The input spectral energy distribution is defined by the AB magnitudes and linear interpolation in between the values Some annotations e The simulated object and brightness was taken from the NICMOS UDF catalogue published in 7 The UDF was observed in the filters 3 3 EXAMPLE 3 23 F425W F606W F775W F814W F850LP and the NICMOS filters F110W and F160W However in the column names we have used the pivot wave length of the filter always in nm and not the less accurate filter name to give the characteristic wavelength
17. arBurst_slitless_2 SPC fits StarBurst_slitless fits StarBurst_images fits StarBurst_slitless_2 STP fits StarBurst_spectra fits SIMDATA s0_template fits WFC3_IR_1400nm_big_psf fits wfc3_ir_f105w_tpass_m01 dat starbi_template fits WFC3_IR_1400nm_psf fits wfc3_ir_f110w_tpass_m01 dat starb2_template fits WFC3_IR_950nm_big_psf fits wfc3_ir_f110w_tpass_m01 fits starb3_template fits WFC3_IR_950nm_psf fits WFC3_UVIS_350nm_psf fits The simulation results 25 The six objects simulated in this example all use the same model image which is WFC IR PSF at 950nm All objects are based on the identical high resolution 26 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES Figure 3 4 The results of the third simulation the direct image left and the slitless image right Only a cutout image of 80 x 130 pix and 200 x 130pix around the simulated objects is shown for the direct and slitless image respectively spectral template starb2_template fits however the template is shifted to different redshift values prior to simulating the images Figure 3 4 shows the direct image and the slitless image in the left and right panels respectively As the redshift increases from bottom to top the emission lines are shifted to longer wavelengths to the right In total the results comprise e the direct image StarBurst_direct fits the slitless image StarBurst_slitless fits the Model Images StarBurst_images fits the Model Spectra StarBurst_spectra f
18. ct image The objects to be simulated are given in a Model Object Table The total passband parameter tpass direct and the object spectra determine the simulated object flux in e s It is possible to add Poisson noise from sources background and readout The final output image will be in units of e s Usage simdirim incat config 4 3 LOW LEVEL TASKS 39 Parameters incat mandatory string The filename of the Model Object Table with the source list to be simulated config mandatory string The name of the aXe configuration file to be used in the simulations tpass_direct mandatory string Total passband of the optical system to be simulated This can be in fits or ASCII format dirima_name optional string The name of the simulated image created by this task If not given a filename is derived from the name of the Model Object Table model_spectra optional string The multi extension fits table with the input spectra to be used in the simulations model_images optional string The multi extension fits image with the image templates to be used in the simulations nx optional int The dimension of the simulated direct image in x ny optional int The dimension of the simulated direct image in y exptime optional float The exposure time If given noise will be added to the simulated direct image bck_flux optional float The background flux rate or a background image both in e
19. dat config WFC3 IR G141 TV2_sim conf output root 0bjMix inlist spec template spectra lis tpass flux wfc3 ir fiiOw tpass m01 dat inlist ima template images lis exptime disp 2000 0 bck flux disp i 4 tpass direct wfc3 ir fi05w tpass mO1 dat exptime dir 100 0 bck flux dir 0 7 Directories and files after the simulation example 4 1s R CONF DATA OUTPUT OUTSIM SIMDATA template images lis template spectra lis CONF Wfc3 abscal IRgi41 Oth sens fits wfc3_abscal_IRg141_3rd_sens fits 30 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES Object 1 Object 5 Object 11 Object 13 Fluz 10 erg em s 1 1 1 2 1 3 1 4 1 5 1 6 1 1 1 2 1 3 1 4 1 5 1 6 Wavelength Wavelength um Figure 3 7 Comparison between the default extracted spectra red solid line and the simulated spectrum dashed blue line for selected objects wfc3_abscal_IRgi4i_ist_sens fits WFC3 IR G141 TV2_sim conf Wfc3 abscal IRgi41 2nd sens fits WFC3 IR G141 TV2_sim conf simul DATA example 4 MOT dat ObjMix_images fits ObjMix_spectra fits OUTPUT OUTSIM ObjMix direct fits ObjMix_slitless_2 SPC fits ObjMix_slitless fits ObjMix_images fits ObjMix_slitless_2 STP fits ObjMix_spectra fits SIMDATA Mann_E dat WFC3_IR_1400nm_big_psf fits wfc3_ir_f105w_tpass_m01 fits Mann_SO dat WFC3 IR 1400nm psf fits Wfc3 ir fii0w tpass m01 dat starb2 template fits WFC3 IR 950nm psf fits starbi templa
20. direct image and using the catalogue in an aXe spectral extraction would avoid this problem 3 3 Example 3 Simulation details instrument of objects object spectrum object brightness flux normalization object shape default extraction direct image WFC3 IR G102 6 high resolution spectra at different redshift defined at 11550A in 10400 10600 template image YES YES filter wfc3_ir_f110w_tpass_m01 dat Directories and files before the simulation example 3 ls R CONF DATA OUTPUT OUTSIM SIMDATA template images lis template spectra lis 24 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES CONF Wfc3 abscal IRg102 Oth sens fits WFC3 IR G102 TV2 sim conf Wfc3 abscal IRg102 1st sens fits Wfc3 abscal IRg102 2nd sens fits DATA example 3 MOT dat OUTPUT OUTSIM SIMDATA s0_template fits WFC3_IR_1400nm_big_psf fits wfc3_ir_f105w_tpass_m01 dat starbi_template fits WFC3_IR_1400nm_psf fits wfc3_ir_f110w_tpass_m01 dat starb2_template fits WFC3_IR_950nm_big_psf fits WFC3_UVIS_350nm_psf fits starb3_template fits WFC3_IR_950nm_psf fits example_3 gt setenv AXE_IMAGE_PATH DATA example_3 gt setenv AXE_OUTPUT_PATH OUTPUT example_3 gt setenv AXE_CONFIG_PATH CONF example_3 gt setenv AXE_OUTSIM_PATH OUTSIM example_3 gt setenv AXE_SIMDATA_PATH SIMDATA The Model Object Table example_3_MOT dat NUMBER X IMAGE Y IMAGE A IMAGE B IMAGE THETA IMAGE MAG F1155W SPECTEMP 2 10 MODIMA
21. e This result comprises in detail e the simulated slitless image example 1 MOT slitless fits e the extracted 1D spectrum example 1 MOT slitless 2 SPC fits e the 2D grism stamp image file example 1 MOT slitless 2 STP fits Figure 3 1 displays the main results of the example the simulated slitless im age left and the extracted spectrum right The blue line marks the input spectrum which is a flat spectrum at the value f corresponding to the given AB magnitude 19 5 1248 1 107 107 7erg cm s Some annotations e The dispersed image in Fig 3 1 shows besides the central first order also the zeroth order left and second order right slitless spectrum e The extracted spectrum appears to differ in flux level from the input spectrum solid and dashed lines in Fig 3 1 The quantitative difference is explained by the finite extraction width which corresponds to the aXe parameter mfwhm 3 0 see Chapt 4 2 1 for an explanation of this parameter e An observant reader may have noticed that after performing the example simulation there is next to the configuration file WFC3 IR G102 TV2 sim conf a file with the similar name WFC3 IR G102 TV2 sim conf simul aXeSIM has created and used in the simulations this variant of the original configu ration file The new configuration file contains a keyword for the telescope area necessary for generating direct images which has the HST collect ing area as de
22. es parameter inlist An ASCII list loadable with the AsciiData module Lines starting with are not loaded The list must contain at least one column and the first column has to be of type string NULL entries are not allowed in the first column Data in possible further columns is not used The entries must point to existing fits images which are located in the directory AXE_SIMDATA_PATH 5 2 Spectrum Template List Used in e simdata parameter inlist_spec e prepspectra parameter inlist Similar to 5 1 but the entries must point to existing fits binary tables or ASCII tables in the directory AXE SIMDATA PATH 5 3 Total Passband File Used in e simdata parameter tput direct e prepspectra parameter tpass flux 43 44 CHAPTER 5 FILE FORMATS A binary fits table with one extension or an ASCII table with two rows The fits table must contain the two columns wavelength and throughput The col umn wavelength contains the wavelength positions in Angstrom in ascending order The column throughput contains the system throughput for the wave length range 0 0 1 0 An ASCII table must contain two columns the first is the wavelength in Angstrom and the second the total throughput The total throughput is the fraction of photons that is recorded on the detector at a given wavelength in All optical components mirrors filters entrance windows and the detector efficiency contribute as factors to the t
23. esim To install them please download them and do the following gt mv aXe 2 1 lt arch gt bin tar gz your aXeSIM path taxe iraf bin gt cd your aXeSIM path taxe iraf bin gt gunzip aXe 2 1 lt arch gt bin tar gz gt tar xvf aXe 2 1 lt arch gt bin tar In the hopefully unlikely case that these binaries do not work or you work with a different operating system you have to build the executables by yourself as described in Chapter 2 3 13 14 CHAPTER 2 INSTALLING AXESIM On the Python side there exists a script to compile the code Go to the Python directory and compile the Python code there with gt cd your aXeSIM path taxe iraf gt python compileaXe py If all went well aXeSIM 1 4 is now ready Since aXeSIM 1 4 the code basis of aXeSIM and the extraction package aXe 2 are united As a consequence the new version 2 1 of aXe is delivered and installed together with aXeSIM 1 4 The new packages with their tasks must be declared in PyRAF To do this add the following lines near the end of your login cl file or in loginuser cl reset taxe21 task taxe21 pkg reset helpdb your aXe2 1 path taxe iraf taxe21 taxe21 cl envget helpdb taxe21 lib helpdb mip reset taxesimi4 7 your aXe2 1 path taxe iraf task taxesimi4 pkg taxesimi4 taxesimi4 cl reset helpdb envget helpdb taxesimi4 lib helpdb mip The next time PyRAF is launched the package aXeSIM and aXe are available aXeSIM can then be
24. example_4 gt setenv AXE_OUTPUT_PATH OUTPUT example_4 gt setenv AXE_CONFIG_PATH CONF example_4 gt setenv AXE_OUTSIM_PATH OUTSIM example_4 gt setenv AXE_SIMDATA_PATH SIMDATA The Model Object Table example 2 MOT dat after a simdata run Unlike the previous examples we have listed here the Model Object Table as it looks after the execution of simdata During the simulations the columns 11 16 were appended No original table entry in 721 7210 was modified NUMBER X IMAGE Y IMAGE A IMAGE B IMAGE THETA IMAGE MAG F1155W SPECTEMP 9 7 10 MODIMAGE ONANBRWNHH 3 4 EXAMPLE 4 29 Figure 3 6 The image results of the fourth simulation the slitless image left and the direct image Only coutouts of 400 x 200pix and 320 x 200pix centered on the objects are shown 11 MODSPEC 12 A_WORLD 13 B_WORLD 14 THETA_WORLD 15 X_WORLD 16 Y_WORLD 1 450 0 170 0 1 6 1 3 270 0 21 0 0 0 0 0 O 1 600000 00 1 300000 00 2 700000 02 5 320378 01 2 778795 01 2 460 0 110 0 1 5 1 2 45 0 21 0 0 0 0 0 O 1 500000 00 1 200000 00 4 500000 01 5 320448 01 2 778852 01 3 450 0 130 0 1 9 1 5 70 0 21 0 5 2 0 3 1 1 900000 00 1 500000e 00 7 000000 01 5 320431 01 2 778826 01 4 450 0 80 0 1 5 1 5 90 0 21 0 0 0 0 0 1 500000 00 1 500000 00 9 000000 01 5 320497 01 2 778865 01 5 500 0 95 0 1 5 1 5 90 0 20 0 3 0 5 1 2 1 500000 00 1 500000 00 9 000000 01 5 320429e 01 2 7
25. fault Moreover the new configuration file always marks the extensions 1 2 and 3 as science error and dq extension As a conse quence aXeSIM simulates only images with one science extension and for simulating ACS WFC and WFC3 UVIS grism images the two chips must 20 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES be treated separately Concerning the essential quantities the descrip tions of trace and dispersion of the various orders there is no difference between the original and the new configuration file and both can be used to extract spectra from the simulated slitless images the original one may need to be corrected to address the correct image extension e A close inspection of the Model Object Table reveals that during the simu lation some additional columns were appended For internal reasons these added columns are necessary for running aXeSIM However these modifica tions to the Model Object Table never change essential simulation input given by the user and repeating a simulation with the modified table will yield the identical simulated images 3 2 Example 2 Simulation details instrument WFC3 IR G102 of objects 1 object spectrum spectral energy distribution defined by several magnitude values object brightness defined by several magnitude values flux normalization not required object shape template image default extraction YES direct image YES filter w c3 ir f105w tpass mO1 dat Directories and files befo
26. flux disp if image e AXE_SIMDATA_PATH content of inlist_spec content of inlist_ima tpass_direct tpass_flux e inlist_spec inlist_spec Output e AXE_OUTSIM PATH all output 4 3 Low Level Tasks As aleady mentioned in previous chapters few users will benefit from using the Low Level Tasks for their simulations The box on page 36 describes a usage scenario based on Low Level Tasks Most users will exclusively work with the High Level Task presented in Sect 4 2 4 3 LOW LEVEL TASKS 37 4 3 1 PREPIMAGES Description This task generates the multi extension fits image with normalized image tem plates to be used in simdata simdispim or simdirim The input is a list of template images in fits format These templates are normalized to an integrated intensity of 1 0 and stored as a multi extension fits image Usage prepimages inlist Parameters inlist mandatory string The Image Template List The template images listed therein must have fits format model_images optional string Name of the multi extension fits images containing the normalized template images Input an Output Input e AXE SIMDATA PATH content of inlist e inlist Output e AXE OUTSIM PATH all output 4 3 2 PREPSPECTRA Description This task generates the multi extension fits table with the spectra to be used by the tasks simdata simdispim or simdirim The task uses as input the template spectra assumed restframe
27. flux in normalization passband is very high due to the strong emission line see Fig 3 5 This results in a large normalization factor and a lower continuum level of this source see object traces in Fig 3 4 as compared to the other objects 3 4 Example 4 Simulation details instrument WFC3 IR G141 of objects 14 object spectrum high resolution spectra and spectral energy distributions object brightness defined at 11550A flux normalization filter wfc3 ir f105w tpass mO1 dat object shape template images and Gaussian shapes default extraction YES direct image YES filter w c3_ir_f105w_tpass_m01 dat Directories and files before the simulation example_4 gt 1s R CONF DATA OUTPUT OUTSIM SIMDATA template_images lis template_spectra lis CONF Wfc3 abscal IRgi41 Oth sens fits wfc3_abscal_IRg141_3rd_sens fits Wfc3 abscal IRgi41 1st sens fits WFC3 IR G141 TV2_sim conf Wfc3 abscal IRg141 2nd sens fits example_4_MOT dat OUTPUT OUTSIM ObjMix_direct fits ObjMix_slitless_2 SPC fits ObjMix_slitless fits ObjMix images fits ObjMix_slitless_2 STP fits ObjMix_spectra fits SIMDATA Mann_E dat starb3_template fits WFC3 IR 950nm psf fits Mann S0 dat WFC3 IR 1400nm big psf fits wfc3 ir fi05w tpass mO1 dat starbi template fits WFC3 IR 1400nm psf fits wfc3_ir_f110w_tpass_m01 dat starb2_template fits WFC3_IR_950nm_big_psf fits WFC3_UVIS_350nm_psf fits example_4 gt setenv AXE_IMAGE_PATH DATA
28. g the tradition of the aXe software package aXeSIM contains two levels of tasks the so called Low Level Tasks and the so called High Level Tasks curently there exists only one of the latter simdata While the Low Level Tasks perform one special step each the High Level Tasks successively do a series of processing steps to generate complete simulated images as output from the basic input The High Level Tasks use the Low Level Tasks for the individual steps The normal user who simulates only one object will likely just use the High Level Task For specific applications and large series of simulations e g to determine limiting depths in deep fields it might have advantages to use the Low Level Tasks saving time if successive steps need to be repeated 4 2 High Level Tasks 4 2 1 SIMDATA Description This task generates the simulated data which is the simulated dispersed image and if requested the simulated direct image simdata comprises all the sim ulation possibilities available in aXeSIM hence this is the only task most users will ever use Internally simdata executes from several to all Low Level Tasks depending on the parameters Usage simdata incat config 33 34 CHAPTER 4 THE AXESIM TASKS Parameters incat mandatory string The filename of the Model Object Table with the source list to be simulated There is a minimal list of columns and additional columns which have to be present for certain d
29. irect image models config mandatory string The name of the aXe configuration file to be used in the simulations output_root optional string Root name for all output products If not given the root name is derived from the name of the Model Object Table silent optional boolean default yes The silent mode reduces the output written to the screen inlist_spec optional string The name of the Spectrum Template List The template spectra therein can have ASCII or fits format tpass_flux optional string Total passband to be used for the scaling of the template spectra in the flux space This is either an ASCII or fits file name or an expression of the form lambda_min lambda_max nm In the latter case the passband has a boxcar shape with lambda min and lambda max as boundaries inlist ima optional string The Image Template List The template images listed therein must have fits format lambda psf optional float The wavelength where the object extent A IMAGE and B IMAGE was determined nx disp optional int The dimension of the simulated dispersed image in x ny_disp optional int The dimension of the simulated dispersed image in y exptime disp optional float The exposure time If given noise will be added to the simulated dispersed image bck flux disp optional float string 4 2 HIGH LEVEL TASKS 35 The background flux rate or a background image both in e s fo
30. ith a table header in the SExtractor format The table has the mandatory columns e NUMBER the object identifier int e X IMAGE the x position of the object pix float e Y IMAGE the y position of the object pix float e A IMAGE the major axis rms pix float e B IMAGE the minor axis rms pix float e THETA IMAGE the position angle of the major axis deg float e MAG number the AB magnitude at the wavelength number nm float There might be several columns with AB magnitudes If the task SIMDATA is run with non empty parameter spec models the table must contain the columns e SPECTEMP which model spectrum to use int e Z redshift of object float If the task is run with the parameter object models the table must contain the column e MODIMAGE which image template to use int NULL entries are not allowed in the mandatory columns Any further columns and table entries are not used 46 CHAPTER 5 FILE FORMATS Chapter 6 Environmental variables aXeSIM uses some of the traditional aXe environmental variables and intro duces two new specific ones The variables and their usage are AXE SIMDATA PATH the path where the template spectra template im ages and total passband files are located AXE_OUTSIM_PATH all output of aXeSIM is written to this directory path AXE IMAGE PATH the path where the model object table is located as input to simdispim simdirim and simdata AXE CONFIG P
31. its e the default extracted 1D spectra StarBurst_slitless_2 SPC fits the 2D grism stamp image file StarBurst_slitless_2 STP fits results start with the string given in the simdata parameter output_root Before simulating the direct and slitless images the template spectra are shifted in redshift and in flux These spectra are stored in the Model Spectra file StarBurst_spectra fits The column MODSPEC which simdata appends to the Model Object Table contains for each object the corresponding extension in the Model Spectra file Figure 3 5 shows a comparison between the default extracted spectra from StarBurst_slitless_2 SPC fits and their corresponding extension in StarBurst_spectra fits for all objects in this example The blue dashed line marks the template and 3 3 EXAMPLE 3 27 6 S 6 4 Object 1 4 Object 2 4 4 3 3 La lt SE M 24 Re i t e 6 55 Object 3 5 5 Object 4 Sa Sa i UU 5 3 A gt ce 1 ol 8 4 Object 5 8 Object 6 3 3 E 4 Ba N 3 En 3 1 2 Fa 2 1 1 4 1 0 80 0 85 0 90 095 100 105 1 10 0 80 0 85 090 0 95 100 1 05 1 10 Wavelength Wavelength Figure 3 5 Comparison between the default extracted spectrum red solid line and the simulated spectrum dashed blue line The green point marks the flux normalization value and the black bar the wavelength interval for the flux normalization the
32. its cor responds to which simulated and extracted object check the Model Ob ject Table here example_2_MOT dat after the simulations The column MODSPEC here 11 contains the corresponding extension number of the object in ObjMix_spectra fits When e g simulating object 3 the already redshifted and flux scaled extension 1 of example 2 MOT dat was used as input spectrum The panel for Object 5 in Fig 3 7 was done plot ting 0bjMix slitless 2 SPC fits beam 5A over ObjMix_spectra fits 2 0 in this column means no spectral template hence a spectral energy dis tribution is used as spectral input e Fig 3 7 object 5 is an example of the extrapolation constant in fA of a spectrum beyond the defined range shown with the blue dotted line e For some objects in Fig 3 7 the extracted flux seems to exceed the input spectra As Fig 3 6 shows contamination the mutual overlap of spectra could be an issue here e Using the passband of an existing filter is natural if observational data in this filter already exists and the simulation is perhaps even based on an according SExtractor catalogue Defining a boxcar passband as in Exam ple 3 3 is more appropriate for purely synthetic data or in cases where the spectral template does not completely cover the intended normalization passband see box on page 25 32 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES Chapter 4 The aXeSIM tasks 4 1 High Level Tasks Low Level Tasks Followin
33. le 1 MOT slitless 2 SPC fits beam 1a 0 2 7 Fluz 10 lerg em 0 0 0 80 0 85 0 90 0 95 1 00 1 05 1 10 1 15 Wavelength Figure 3 1 The results of the first simulation the simulated slitless image in the left panel left panel and the default extracted spectrum solid red line in comparison to the input spectrum dashed blue line in the right panel The extraction box did not include all the source flux example i setenv AXE OUTPUT PATH OUTPUT example i setenv AXE CONFIG PATH CONF example i setenv AXE OUTSIM PATH OUTSIM The Model Object Table example 1 MOT dat 1 NUMBER 2 X IMAGE 3 Y IMAGE 4 A IMAGE 5 B IMAGE 6 THETA IMAGE 7 MAG F1248W 1 512 0 512 0 2 0 1 0 30 5 19 5 HEH RE The simulation command gt simdata incat example 1 MOT dat config WFC3 IR G102 TV2_sim conf extraction YES Directories and files after the simulation example 1 ls R CONF DATA OUTPUT OUTSIM CONF wfc3_abscal_IRg102_Oth_sens fits wfc3_abscal_IRgi02_2nd_sens fits WFC3 IR G102 TV2 sim conf simul wfc3 abscal IRgi02 ist sens fits WFC3 IR G102 TV2_sim conf example_1_MOT dat OUTPUT OUTSIM example 1 MOT slitless 2 SPC fits example 1 MOT slitless 2 STP fits example 1 MOT slitless fits 3 1 EXAMPLE 1 19 The simulation results As already mentioned in Sect 1 3 aXeSIM collects all output in the directory AXE_OUTSIM_PATH which is OUTSIM in this exampl
34. loaded as any other package by simply typing its name taxesimi4 The aXeSIM software package 1 4 was developed by the Slitless Spectroscopy Group of the ST ECF Maintenance is provided by the Space Telescope Science Institute Further information is available at http www stsci edu resources software_hardware stsdas axe Any questions regarding this software can be directed to help stsci edu taxesim14 tprepimages tprepspectra tsimdata tsimdirim tsimdispim The message which appears during the loading of the package and the task overview indicate that everything went OK and that the tasks can be used from now on The package can be used by more than one user Other users only have to modify their login cl or loginuser cl as described above to access the aXeSIM package and the tasks within it of course provided that they have access to the installation directory aXeSIM was successfully built and tested under Fedora 6 It should be no prob lem to install aXeSIM under other Unix or Unix like operating systems such as HPUX or MacOSX 2 3 COMPILING THE C CODE 15 2 3 Compiling the C code To compile the C code you need e a compiler such as GNUC CC e GNU Scientific Libraries http www gnu org software gsl e WCStools 3 x libraries http tdc www harvard edu software wcstools e CFITSIO 3 x libraries http heasarc gsfc nasa gov docs software fitsio fitsio html For the C part a configure script is included with
35. of the filter The total passband see Sect 5 3 for a definition of the direct image was given as the ASCII table wfc3_ir_f105w_tpass_m01 dat and transformed to the equivalent fits file w c3 ir f105w tpass mO1 fits in aXeSIM The default extraction of aXeSIM uses like aXe the columns A IMAGE and B IMAGE in the object table to determine the extraction width For the def initely extended object in the image template see Fig 3 3 the tentative value 8 0 was given An independent SExtractor run on the direct image would deliver the correct value The Gauss parameters A IMAGE B IMAGE and THETA IMAGE are not used when making the simulated images since the object shape is defined with a template image There are a number of reasons why the default extracted spectrum does not completely coincide with the input spectrum in Fig 3 3 As in the first example there is a wiggle on the long wavelength end due to the object extent and the drop in sensitivity Also when using image templates care must be taken to put the sources into the centre of the template aXeSIM puts the centre of the template image at the nominal position given in the Model Object Table and the default extraction also uses this position for the extraction An off centre template source results in a wavelength shift between the simulation and the extraction which can translate into a flux difference between the simulated and the extracted spectrum Running SExtractor on the
36. on fits image with the image templates to be used in the simulations nx optional int The dimension of the simulated dispersed image in x 4 3 LOW LEVEL TASKS 41 ny optional int The dimension of the simulated dispersed image in y exptime optional float The exposure time If given noise will be added to the simulated dispersed image bck_flux optional float The background flux rate or a background image both in e s extraction optional boolean default yes Flag to initiate a basic spectral extraction on the simulated dispersed image extrfwhm optional float default 3 0 Factor to set the extraction width orient optional boolean default yes Whether to use tilted extracted This is the default When set to no only vertical extraction along columns is performed slitless_geom boolean default yes Whether to use an extraction orientation which is optimized for slitless spectroscopy adj_sens boolean default yes Adjust sensitivity for extended objects silent optional boolean default yes The silent mode reduces the output written to the screen Input an Output Input e AXE IMAGE PATH incat model_spectra model images e AXE CONFIG PATH config bck flux if image Output e AXE OUTSIM PATH all output 42 CHAPTER 4 THE AXESIM TASKS Chapter 5 File Formats 5 1 Image Template List Used in e simdata parameter inlist_ima e prepimag
37. otal throughput 5 4 Template Spectrum Files listed in the Spectrum Template List simdata parameter inlist spec are all Template Spectra An ASCII or binary fits table The table contains exactly two columns with float values The first column contains the ascending wavelength positions in A The second column contains the associated flux values in erg s cm NULL elements are not allowed 5 5 Template Image Files listed in the Image Template List simdata parameter inlist_ima are all Template Images binary fits image with at most two extensions In case of two extensions the first extension must be empty and the second contain the data In case of one extension only this extension must contain data 5 6 Model Images Used in e output of simdata and prepimages e simdispim parameter model images e simdirim parameter model images A multi dimension binary fits image Each extension contains one image with the integrated intensity 1 0 5 7 Mlodel Spectra Used in 5 8 MODEL OBJECT TABLE 45 e output of simdata and prepspectra e simdispim parameter model spectra e simdirim parameter model spectra A multi dimension binary fits table Each extension contains a table with the two columns wav nm nm and flux erg cm s A 5 8 Model Object Table Used in e simdata parameter incat e simdispim parameter incat e simdirim parameter incat An ASCII table loadable with AsciiData module w
38. r the dispersed image extraction optional boolean default yes Flag to initiate a basic spectral extraction on the simulated dispersed image extrfwhm optional float default 3 0 Factor to set the extraction width orient optional boolean default yes Whether to use tilted extracted This is the default When set to no only vertical extraction along columns is performed slitless_geom boolean default yes Whether to use an extraction orientation which is optimized for slitless spectroscopy adj_sens boolean default yes Adjust sensitivity for extended objects tpass_direct optional string Total passband of the optical system to be simulated The can be in fits or ASCII format In case this parameter is not given no direct image will be produced nx_dir optional int The dimension of the simulated direct image in x ny_dir optional int The dimension of the simulated direct image in y exptime_dir optional float The exposure time If given noise will be added to the simulated direct image bck_flux_dir optional float string The background flux rate or a background image both in e s for the direct image version optional string Parameter to always have the version number accessible No need to ever change use or even touch it 36 CHAPTER 4 THE AXESIM TASKS Input and Output Input e AXE_IMAGE_PATH incat e AXE CONFIG PATH config bck flux dir and bck
39. re the simulation sia R CONF DATA OUTPUT OUTSIM SIMDATA template images lis CONF Wfc3 abscal IRg102 Oth sens fits wfc3 abscal IRg102 2nd sens fits Wfc3 abscal IRgi02 1st sens fits WFC3 IR G102 TV2 sim conf example_2_MOT dat OUTPUT OUTSIM SIMDATA spiral_1 fits wfc3_ir_f105w_tpass_m01 dat WFC3_IR_1400nm_psf fits WFC3_UVIS_350nm_psf fits WFC3 IR 950nm psf fits 7 gt AXE IMAGE PATH DATA 7 setenv AXE OUTPUT PATH OUTPUT setenv AXE CONFIG PATH CONF 7 setenv AXE SIMDATA PATH SIMDATA setenv AXE OUTSIM PATH OUTSIM The Model Object Table example 2 MOT dat NUMBER X IMAGE Y IMAGE A IMAGE B IMAGE THETA IMAGE MAG F432W 3t dob b db d Gb onme6ovn 3 2 EXAMPLE 2 21 Figure 3 2 The results of the second simulation the direct image left and the slitless image right Both images are displayed with a logarithmic lookup table to enhance the contrast 8 MAG_F592W 9 MAG F769W 10 MAG F906W 11 MAG F1123W 12 MAG F1603W 13 MODIMAGE Ren 269 312 0 512 0 8 0 8 0 90 0 22 984 22 163 21 890 21 807 22 027 21 788 4 The Image Template List template images lis more template images lis WFC3 IR 1400nm psf fits WFC3 IR 950nm psf fits WFC3 UVIS 350nm psf fits spiral 1 fits The simulation command gt simdata incat example 2 MOT dat config WFC3 IR G102 1V2 sim conf inlist ima template images lis tpass direct wfc3 ir fi05w tpa
40. rently not included in the aXeSIM simulations e non linear detector effects such as saturation or blooming are not simu lated e aXeSIM neither adds dark current nor takes dark current into account in the noise model e aXeSIM does not include a detector or large scale flatfield in the simula tions e images simulated with aXeSIM do not have intra pixel sensitivity variations as images from real detectors e g NICMOS do e aXeSIM takes as input object positions and sizes only as pixel coordinates on the detector No attempt is made to correct for instrument distortions from sky to detector Users can compensate some of these aXeSIM deficiencies e g by adding the dark current to the sky background or applying non linear effects on aXeSIM images 1 5 General use of aXeSIM aXeSIM was developed for the slitless spectroscopic modes of the HST instru ments WFC3 ACS NICMOS 1 6 THE PYRAF MODULE 11 However aXeSIM is not restricted to be used for HST and HST intruments only The software can be used for any telescope and instrument which can be described with aXe configuration and calibration files and the parameters offered by aXeSIM e g a sky which is described either in e s hence flat or with a sky image in e s To use aXeSIM for simulating data for a new telescope instrument you have to e create a new aXe configuration file describing the trace and dispersion solutions for all spectral orders see Sect 5 2
41. s ACS and NICMOS An option of the simulator is to produce a direct image through a selected filter to match the slitless spectrum image The simulation package uses the same components as used by aXe 2 for the extraction of slitless spectra and thus aims at spectrophotometric integrity useful for observation design but essential for the quantitative assessment of slitless data The simulation package will help HST users during their Phase I and Phase II proposal preparation to e gain a 2D impression of the layout of the target field and the likely prob lems to be encountered in slitless spectroscopy e g crowding spectral overlap presence of bright spectra e check the exposure time to determine a given signal to noise in a 2D spec trum The spectroscopic ETC s at the STScI provide more flexible deter mination of S N for an individual 1D spectrum e by adjustment determine the optimal pointing and roll angle for a specific target field such as to minimize the contamination of spectra of interest e learn what to expect in terms of spectral resolution and sensitivity from slitless spectra and thus choose the best instrument and configuration e and incidentally become familiar working with and reducing slitless spec troscopic data with the aXe package While the primary motivation to start the aXeSIM project was WFC3 with its three grisms aXeSIM will also work for all the ACS grism and prism modes T 8 CHAPTER 1 DESCRI
42. ss m01 dat Directories and files after the simulation gt ls R CONF DATA gaga txt OUTPUT OUTSIM SIMDATA template images lis CONF Wfc3 abscal IRg102 Oth sens fits WFC3 IR G102 TV2 sim conf Wfc3 abscal IRg102 1st sens fits WFC3 IR G102 TV2 sim conf simul Wfc3 abscal IRg102 2nd sens fits DATA example 2 MOT dat template images fits OUTPUT OUTSIM example_2_MOT_direct fits example_2_MOT_slitless fits example_2_MOT_slitless_2 SPC fits template_images fits example_2_MOT_slitless_2 STP fits SIMDATA spiral_1 fits wfc3_ir_f105w_tpass_m01 dat WFC3_IR_1400nm_psf fits wfc3_ir_f105w_tpass_m01 fits WFC3 IR 950nm psf fits WFC3_UVIS_350nm_psf fits 22 CHAPTER 3 ILLUSTRATED AXESIM EXAMPLES lt spectral energy distribution from AB mags AD NEL 5 1 01 example 2 MOT slitless 2 SPC fits beam_269a 5 0 E 0 n n 0 80 0 85 0 90 0 95 1 00 1 05 1 10 1 15 1 20 Wavelength Figure 3 3 Left panel Comparison between the default extracted spectrum red solid line and the input spectrum dashed blue line a spectral energy distribution defined by the AB magnitude values Right panel The image template The simulation results In the Model Object Table the column MODIMAGE contains the value 4 thus pointing to the fourth entry in the Image Template List This entry named spiral_1 fits is then used as the image template when simulating the direct and dispersed image The spir
43. tains the total system throughput mirror instrument detector as a function of wavelength for the direct image to be simulated The set of direct image slitless image will be identical to an ideal observed direct image slitless image pair in standard ACS WFCS3 slitless observations 10 CHAPTER 1 DESCRIPTION This means that a positional offset which might be applied in the observations by default as it is the case for e g ACS data with HRC PR200L will also be present in the simulated images Sky background provided by the user either as single value or background image file in e s and random noise readout and photon noise from back ground and objects can be added to the output images It is possible to close the loop by performing a simple aXe extraction at the end of the simulations in aXeSIM Alternatively the user can use SExtractor on the direct images and then perform a standard extraction using the original aXe software Making the spectral extractions on the simulated data is very important to for example check the detectability of spectral features as a func tion of the signal to noise ratio or to make completeness and reliability tests for scientific publications All final output of aXeSIM is written to the directory to which the environ mental variable AXE_OUTSIM_PATH is pointing to see Sect 6 1 4 Limitations of aXeSIM There are a number of effects and features in real data that are cur