%APN3_PROCEEDINGS_FORM%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % TEMPLATE.TEX -- APN3 (2003) ASP Conference Proceedings template. % % Derived from ADASS VIII (98) ASP Conference Proceedings template % Updated by N. Manset for ADASS IX (99), F. Primini for ADASS 2000, % D.Bohlender for ADASS 2001, and H. Payne for ADASS XII and LaTeX2e. % % Use this template to create your proceedings paper in LaTeX format % by following the instructions given below. Much of the input will % be enclosed by braces (i.e., { }). The percent sign, "%", denotes % the start of a comment; text after it will be ignored by LaTeX. % You might also notice in some of the examples below the use of "\ " % after a period; this prevents LaTeX from interpreting the period as % the end of a sentence and putting extra space after it. % % You should check your paper by processing it with LaTeX. For % details about how to run LaTeX as well as how to print out the User % Guide, consult the README file. You should also consult the sample % LaTeX papers, sample1.tex and sample2.tex, for examples of including % figures, html links, special symbols, and other advanced features. % % If you do not have access to the LaTeX software or a laser printer % at your site, you can still prepare your paper following the % instructions in the User Guide. In such cases, the editors will % process the file and make any necessary editorial adjustments. % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % \documentclass[11pt,twoside]{article} % Leave intact \usepackage{adassconf} % If you have the old LaTeX 2.09, and not the current LaTeX2e, comment % out the \documentclass and \usepackage lines above and uncomment % the following: %\documentstyle[11pt,twoside,adassconf]{article} \begin{document} % Leave intact %----------------------------------------------------------------------- % Paper ID Code %----------------------------------------------------------------------- % Enter the proper paper identification code. The ID code for your % paper is the session number associated with your presentation as % published in the official conference proceedings. You can % find this number locating your abstract in the printed proceedings % that you received at the meeting or on-line at the conference web % site; the ID code is the letter/number sequence proceeding the title % of your presentation. % % This will not appear in your paper; however, it allows different % papers in the proceedings to cross-reference each other. Note that % you should only have one \paperID, and it should not include a % trailing period. % % EXAMPLE: \paperID{O4-1} % EXAMPLE: \paperID{P7-7} % \paperID{P10-3} %%%% ID=P10-3 %----------------------------------------------------------------------- % Paper Title %----------------------------------------------------------------------- % Enter the title of the paper. % % EXAMPLE: \title{A Breakthrough in Astronomical Software Development} % % If your title is so long as to fill the page header when you print it, % then please supply a short form as a \titlemark. % % EXAMPLE: % \title{Rapid Development for Distributed Computing, with Implications % for the Virtual Observatory} % \titlemark{Rapid Development for Distributed Computing} % \title{Model Based Corrections to Data from Radiation Damaged Detectors.} \titlemark{Modelling Damaged Detectors} %----------------------------------------------------------------------- % Authors of Paper %----------------------------------------------------------------------- % Enter the authors followed by their affiliations. The \author and % \affil commands may appear multiple times as necessary (see example % below). List each author by giving the first name or initials first % followed by the last name. Authors with the same affiliations % should grouped together. % % EXAMPLE: \author{Raymond Plante, Doug Roberts, % R.\ M.\ Crutcher\altaffilmark{1}} % \affil{National Center for Supercomputing Applications, % University of Illinois Urbana-Champaign, Urbana, IL % 61801} % \author{Tom Troland} % \affil{University of Kentucky} % % \altaffiltext{1}{Astronomy Department, UIUC} % % In this example, the first three authors, "Plante", "Roberts", and % "Crutcher" are affiliated with "NCSA". "Crutcher" has an alternate % affiliation with the "Astronomy Department". The fourth author, % "Troland", is affiliated with "University of Kentucky" \author{Paul Bristow} \affil{ST-ECF, ESO, Karl-Schwarzschild-Str. 2, D-85748, Garching bei M$\ddot{\rm u}$nchen, Germany} %----------------------------------------------------------------------- % Contact Information %----------------------------------------------------------------------- % This information will not appear in the paper but will be used by % the editors in case you need to be contacted concerning your % submission. Enter your name as the contact along with your email % address. % % EXAMPLE: \contact{Dennis Crabtree} % \email{crabtree@cfht.hawaii.edu} % \contact{Paul Bristow} \email{bristowp@eso.org} %----------------------------------------------------------------------- % Author Index Specification %----------------------------------------------------------------------- % Specify how each author name should appear in the author index. The % \paindex{ } should be used to indicate the primary author, and the % \aindex for all other co-authors. You MUST use the following % syntax: % % SYNTAX: \aindex{Lastname, F. M.} % % where F is the first initial and M is the second initial (if % used). This guarantees that authors that appear in multiple papers % will appear only once in the author index. % % EXAMPLE: \paindex{Crabtree, D.} % \aindex{Manset, N.} % \aindex{Veillet, C.} % % NOTE: this information is also used to build the author list that % appears in the table of contents. Authors will be listed in the order % of the \paindex and \aindex commmands. % \paindex{Bristow, P.} %\aindex{ } % Remove this line if there is only one author %----------------------------------------------------------------------- % Author list for page header %----------------------------------------------------------------------- % Please supply a list of author last names for the page header. in % one of these formats: % % EXAMPLES: % \authormark{Lastname} % \authormark{Lastname1 \& Lastname2} % \authormark{Lastname1, Lastname2, ... \& LastnameN} % \authormark{Lastname et al.} % % Use the "et al." form in the case of seven or more authors, or if % the preferred form is too long to fit in the header. \authormark{Bristow} %----------------------------------------------------------------------- % Subject Index keywords %----------------------------------------------------------------------- % Enter a comma separated list of up to 6 keywords describing your % paper. These will NOT be printed as part of your paper; however, % they will be used to generate the subject index for the proceedings. % There is no standard list; however, you can consult the indices % for past proceedings (http://adass.org/adass/proceedings/). % % EXAMPLE: \keywords{visualization, astronomy: radio, parallel % computing, AIPS++, Galactic Center} % % In this example, the author noticed that "radio astronomy" appeared % in the ADASS VII Index as "astronomy" being the major keyword and % "radio" as the minor keyword. The colon is used to introduce another % level into the index. \keywords{instrument modelling, CCD, detector read out, radiation damage, pipelines} %----------------------------------------------------------------------- % Abstract %----------------------------------------------------------------------- % Type abstract in the space below. Consult the User Guide and Latex % Information file for a list of supported macros (e.g. for typesetting % special symbols). Do not leave a blank line between \begin{abstract} % and the start of your text. \begin{abstract} % Leave intact Space based CCDs suffer continual bombardment from the hostile radiation environment which gradually degrades their performance and potentially limits their operational lifetime. As part of our effort to enhance the calibration of STIS (a spectrograph on-board the Hubble Space Telescope), we have developed a model of the readout process for CCD detectors suffering from degraded charge transfer efficiency. The model enables us to make predictive corrections to data obtained with such detectors. We present examples of the corrections possible using this technique and compare them to what can be achieved using a more conventional empirical approach. In addition we discuss some of the difficulties of providing users with automated implementations of this this kind of data analysis software.% Place the text of your abstract here - NO BLANK LINES \end{abstract} %----------------------------------------------------------------------- % Main Body %----------------------------------------------------------------------- % Place the text for the main body of the paper here. You should use % the \section command to label the various sections; use of % \subsection is optional. Significant words in section titles should % be capitalized. Sections and subsections will be numbered % automatically. % % EXAMPLE: \section{Introduction} % ... % \subsection{Our View of the World} % ... % \section{A New Approach} % % It is recommended that you look at the sample papers, sample1.tex % and sample2.tex, for examples for formatting references, footnotes, % figures, equations, html links, lists, and other special features. \section{Introduction} Charge Coupled Devices (CCDs) operating in hostile radiation environments suffer a gradual decline in their Charge Transfer Efficiency (CTE, or equivalently, an increase in charge transfer inefficiency, CTI). STIS and WFPC2 have both had their CTE monitored during their operation in orbit and both indeed show a measurable decline in CTE which has reached a level which can significantly effect scientific results (eg. Cawley et al 2001, Heyer 2001, Kimble, Goudfrooij and Gililand 2000). As part of the Instrument Physical Modelling Group's effort to enhance the calibration of STIS we have developed a model of the readout process for CCD detectors suffering from degraded charge transfer efficiency. The model enables us to make predictive corrections to data obtained with such detectors. \section{The Model} Detailed discussion of the model development and the physics involved can be found in Bristow \& Alexov et al. 2002 and Bristow 2003a. Our approach is to simulate the readout process at the level of individual charge transfers. That is we take an image (a charge distribution on a two dimensional pixel array) and transfer the charges out as they would be on a real chip. Throughout we keep track of the status of bulk traps in the silicon pixels as they interact with the charge distribution. The timescales and densities for these known traps are appropriate to the operating temperature and on-orbit radiation exposure respectively. The model has been optimised for the correction of STIS data, but could in principle be ported to other detectors. \section{Cleaning CTE Trails} The clearest aesthetic diagnostic of data suffering from poor CTE is the presence of trails under bright objects. This can be seen clearly in the section of STIS data shown in figure 1 (left), the read out direction is upwards. Figure 1 (right) shows the success of the simulation derived correction in cleaning these trails. \begin{figure} \plottwo{P10-3_1a.eps}{P10-3_1b.eps}%{P10-3_1b.eps} %%% P10-3_1b.eps INERROR \caption{Left: A section of STIS image data suffering from significant CTI. Right: The same section after correction with the physical model. Note that trails under bright sources have been removed} \end{figure} \section{Photometric Corrections} Probably the most important effect of CTI is the loss of flux from the central isophotes of sources. It is possible to calibrate an empirical flux correction as a function of signal strength, background, epoch and position on the chip. Such a correction must be formulated and calibrated differently for photometric and spectroscopic data because of the differing nature of the spatial distributions of illumination and resulting charge. Moreover, empirical corrections {\it only apply to point sources}. On the other hand, modelling the readout process we are able to correct for any charge distribution and can therefore apply this method to all data whether photometric or spectroscopic and obtain a correction for every pixel, not just extracted sources or spectra. Nevertheless the empirical corrections for STIS provide an ideal means of testing and calibrating the physical model, as the empirical corrections are essentially a distillation of what is to be learnt from the calibration data with respect to CTI. If the physical model reproduces empirical results on average for point sources then it is reasonable to conclude that it is correctly modifying the charge distribution and will also therefore correctly predict the CTI in extended sources and indeed the whole image array. \begin{figure} \plotfiddle{P10-3_2a.eps}{90.0mm}{-90.0}{40}{50}{-145.0}{275.0} \caption{Comparison between empirical and model based corrections } \end{figure} A comparison between model based and empirical corrections, for sources to which the empirical corrections apply, is shown if figure 2. Beyond the general good agreement, there are many sources for which the model based and empirical corrections differ significantly. The scatter is due to the fact that the non uniformity of the charge distribution causes the CTI experienced by each source to vary in a way which cannot be accounted for in the empirical corrections. Indeed, if we examine sources corresponding to outlying points in figure 2 in the raw image array, we find that the anomalous correction factor assigned by the physical model is easily understood by considering charge distribution in the surrounding pixels. For example, nearby sources, falling between the source in question and the read out register, will trail charge into the aperture, leading to a smaller CTI effect than the empirical calibration would suggest. (See Bristow 2003a\&b). \begin{figure} \plotone{P10-3_4.eps} \caption{Schematic showing the preparation of CTI corrected data for the CALSTIS pipeline} \end{figure} \section{Pipeline Integration} A complex and comprehensive data pipeline already exists for STIS. It relies upon a database of empirically derived and continually updated reference files selected by header keywords in each dataset. Introducing a model based component of the calibration leads to some conflicts. Some aspects of the calibration which fit neatly into one reference file have more than one physical source and vice versa. Specifically: \begin{itemize} \item Reference files (bias and dark) must themselves be corrected for CTI effects \item The readout simulation generates hot columns from the hot pixels and thereby includes a correction for these features as well as CTI. However, the bias files provided for use in the pipeline, include these hot columns and other features not dealt with by the readout simulation. \end{itemize} However, a complete model based calibration of STIS is not yet possible. In addition, the simulation is CPU intensive and adds considerably to the total processing time, therefore the possibility to execute this as a stand alone process is also desirable. Figure 3 illustrates the incorporation of the model in a way which takes the above into account. %----------------------------------------------------------------------- % References %----------------------------------------------------------------------- % List your references below within the reference environment % (i.e. between the \begin{references} and \end{references} tags). % Each new reference should begin with a \reference command which sets % up the proper indentation. Observe the following order when listing % bibliographical information for each reference: author name(s), % publication year, journal name, volume, and page number for % articles. Note that many journal names are available as macros; see % the User Guide listing "macro-ized" journals. % % EXAMPLE: \reference Hagiwara, K., \& Zeppenfeld, D.\ 1986, % Nucl.Phys., 274, 1 % \reference H\'enon, M.\ 1961, Ann.d'Ap., 24, 369 % \reference King, I.\ R.\ 1966, \aj, 71, 276 % \reference King, I.\ R.\ 1975, in Dynamics of Stellar % Systems, ed.\ A.\ Hayli (Dordrecht: Reidel), 99 % \reference Tody, D.\ 1998, \adassvii, 146 % \reference Zacharias, N.\ \& Zacharias, M.\ 2003, % \adassxii, \paperref{P7.6} % % Note the following tricks used in the example above: % % o \& is used to format an ampersand symbol (&). % o \'e puts an accent agu over the letter e. See the User Guide % and the sample files for details on formatting special % characters. % o "\ " after a period prevents LaTeX from interpreting the period % as an end of a sentence. % o \aj is a macro that expands to "Astron. J." See the User Guide % for a full list of journal macros % o \adassvii is a macro that expands to the full title, editor, % and publishing information for the ADASS VII conference % proceedings. Such macros are defined for ADASS conferences I % through XI. % o When referencing a paper in the current volume, use the % \adassxii and \paperref macros. The argument to \paperref is % the paper ID code for the paper you are referencing. See the % note in the "Paper ID Code" section above for details on how to % determine the paper ID code for the paper you reference. % \begin{references} \reference Bohlin, R.\ \& Goudfrooij, P.\ 2003, STIS Instrument Science Report 2003-03 \reference Bristow, P.\ \& Alexov, A.\ 2002, CE-STIS-Instrument Science Report 2002-001 \reference Bristow, P.\ 2003a CE-STIS-Instrument Science Report 2003-003, in preparation \reference Bristow, P.\ 2003b CE-STIS-Instrument Science Report 2003-001 \reference Bristow, P.\ 2003c CE-STIS-Instrument Science Report 2003-002 \reference Cawley, L., Goudfrooij, P.\ \& Whitmore, B.\ 2001, Instrument Science Report WFC3 2001-05 \reference Goudfrooij, P.\ \& Kimble, R. A.\ 2002 in Proceedings of the 2002 HST Calibration Workshop, Eds Arribas, S., Koekemoer, A and Whitmore, B. (Space Telescope Science Institute) \reference Heyer, I.,\ 2001, WFPC2 Instrument Science Report 2001-009 \reference Kimble, R. A., Goudfrooij, P.\ \& Gililand, R.L.\ 2000, Proc. SPIE Vol. 4013, p. 532-544, in UV, Optical, and IR Space Telescopes and Instruments, Ed. J. B. Breckinridge; P. Jakobsen \end{references} % Do not place any material after the references section \end{document} % Leave intact