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arXiv:1001.0039v1 [astro-ph.IM] 30 Dec 2009Astronomical Data Analysis Software and Systems XIX P45 |
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ASP Conference Series, Vol. XXX, 2009 |
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Y. Mizumoto, K.-I. Morita, and M. Ohishi, eds. |
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TGCat, The Chandra Transmission Grating Catalog and |
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Archive: Systems, Design and Accessibility |
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Arik W. Mitschang1, David P. Huenemoerder2, Joy S. Nichols1 |
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Abstract. The recently released Chandra Transmission Grating Catalog and |
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Archive, TGCat, presents a fully dynamic on-line catalog allowing users to |
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browse and categorize Chandra gratings observations quickly and easily, gen- |
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erate custom plots of resulting response corrected spectra on- line without the |
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need for special software and to download analysis ready product s from multi- |
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ple observations in one convenient operation. TGCathas been registered as |
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a VO resource with the NVO providing direct access to the catalogs in terface. |
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The catalog is supported by a back-end designed to automatically fe tch newly |
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public data, process , archive and catalog them, At the same time ut ilizing an |
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advanced queue system integrated into the archive’s MySQL datab ase allowing |
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large processing projects to take advantage of an unlimited numbe r of CPUs |
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across a network for rapid completion. A unique feature of the cat alog is that |
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all of the high level functions used to retrieve inputs from the Chan dra archive |
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and to generate the final data products are available to the user in an ISIS writ- |
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ten library with detailed documentation. Here we present a structu ral overview |
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of the Systems, Design, and Accessibility features of the catalog a nd archive. |
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1. Introduction |
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TGCataims to be the definitive end-user source for all Chandra HETG S and |
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LETGS observations. In order to achieve this goal the catalo g must both have |
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the absolute best processed and calibrated data, as well as h ave an interface |
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which makes it easy for users to find, review and download thei r observations |
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of choice. The science requirements for accurately process ing gratings data are |
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discussed elsewhere ( Huenemoerder et. al. 2010 ). This writ ing will focus on |
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the automated system that collects and processes new public data, the interfaces |
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used for administrative review, and the interfaces and syst ems provided for user |
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access. |
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2. Database, Archive, and Subsystems |
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TheTGCatprocessing system is comprised of three major components: |
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•MySQL database storing meta-data |
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•File archive |
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•Processing Software |
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1Smithsonian Astrophysical Observatory, Cambridge, MA, US A |
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2MIT Kavli Institute for Space Research, Cambridge, MA |
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12 MITSCHANG, HUENEMOERDER, NICHOLS |
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Figure 1. TGCatdata flow |
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These components are described in the context of TGCatprocessing in this |
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section. |
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Tables: Thetables relevant toprocessingincludetheextractions, source, spec- |
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tral properties, files, and queue tables. The extractions ta ble has one entry per |
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processed extraction, where extraction is taken to mean a si ngle source in a |
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uniqueChandra observation ID (ObsID). Any one ObsIDcan have many sources |
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and any one source can be in many ObsIDs, the extractions tabl e will store one |
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entry for each combination thereof. In order to consolidate all extractions of a |
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single source, there is a source table indexed on SIMBAD1identifier, a TGCat |
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identifier, and coordinates, that associates entries in the extractions table. The |
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files table tracks processing output products and summary im ages allowing the |
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webpagestoeasily displayinformation onfilesavailable fo rdownload. Thespec- |
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tral properties table stores and indexes spectral properti es in several different |
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wavebands, these data are also available in a fits table for do wnload. |
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Data Flow: The flow of data through the system is rather simple, as illus- |
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trated in Figure 1. A bash script run via cronat regular intervals downloads a |
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list of gratings observations from the public chandra archi ve2and compares with |
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the list of ObsIDs that have been submitted to TGCat. Any not in TGCat |
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will be added to the queue table to be processed in line. Daemo n processes, |
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written in python, run on any number of network connected hos ts continuously |
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requesting entries from the queue in a FIFOmanner, the first process to ask |
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entries from the queue table will retrieve the first entry ( by time of creation |
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). They then parse the queue entry which can contain a number o f custom |
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processing parameters, setup work spaces and logging, fork off the processing |
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which is implemented in ISIS ( Houck & Denicola 2000 ) interac tive library |
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functions, which are available for download3and custom use, and finally ingest |
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1http://simbad.u-strasbg.fr/simbad |
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2http://cda.harvard.edu/chaser/ |
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3http://space.mit.edu/cxc/analysis/tgcatTGCat 3 |
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data into the database and archive. During the ingest step, s everal checks are |
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done to evaluate whether or not the resultant processed data are a complete |
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set and worth being manually reviewed by TGCatscientists. If so, meta data |
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are added to the database’s main extractions table which ret urns a unique iden- |
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tifier that is then used to tag the file based products. At this t ime linking is |
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done between the source table and extractions table. If not, the queue entry is |
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marked as an error and notification sent. TGCatoperators have the choice to |
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investigate the existing processing workspace or simply re -evaluate parameters |
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and re-queue the extraction as new. |
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Validation and Verification: Each extraction available for browsing has |
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been reviewed by a member of the TGCatscience team in order to confirm |
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zeroth order placement, proper masking, etc. This is done vi a an internal web- |
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site nearly mimicking the public interface for reviewing ex tractions but with |
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the addition of forms for queueing processing and for markin g the extraction as |
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“good”, “bad”, or “warning” and optional comment fields whic h are available |
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for review by the end user. “bad” extractions are never shown on the public |
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site and administrators have the option of rejecting any oth er extraction for |
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whatever reason. Because each extraction is tagged with the date of processing, |
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the version of TGCatused for processing, and a so called group ID which is |
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unique per group of extractions intended to be of the same obj ect for a single |
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ObsID, keeping track of accepted sources and avoiding dupli cates is made easy. |
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3. Access |
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TGCathas several interfaces for data access. Currently three are operational |
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includingthewebbrowserinterface, andtwoVirtualObserv atoryaccessprotocol |
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interfaces. Each oftheseaccess interfaces areimplemente dasa“plug-in”written |
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in php. Plug-in functions to create output are called by a cat alog independent |
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generalized query library written in php under TGCatdevelopment dubbed |
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“queryLib”. This modular approach makes it trivial to add ac cess interfaces to |
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TGCat. |
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queryLib: queryLib stores state and type information of an individual query |
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in a database table. Each time a query is performed, fields in t his table such as |
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awhereclause, sort fields, indexed IDs and columns are populated wi th infor- |
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mation specific to that query. As a user interacts with the par ticular interface, |
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information in this table entry are updated to reflect the new state of the query |
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through object method calls. queryLib initialized a query b y creating a new en- |
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try in the table with two unique IDs: one is the primary key ide ntifier assigned |
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at creation and can be used to reference the query, the other i s created on the fly |
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using a combination of the primary key and a random hash strin g that is very |
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unlikely to be guessed. This is done so that a malicious user c annot change the |
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state of anyone’s query by simply guessing an ID. The queryLi b speeds up the |
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process of redrawing a table of results by storing the indexe d primary keys of |
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all entries selected rather than having to rerun a potential ly complicated where |
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clause.4 MITSCHANG, HUENEMOERDER, NICHOLS |
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Web Catalog Interface: The web interface4toTGCatallows users browse |
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extraction and object entries in a way that is most suitable t o the catalog data |
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structure. Each extraction has an associated preview page w here a set of stan- |
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dard plots produced at the time of processing is available fo r viewing. A table |
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of spectral properties providing quick general categoriza tion, and a table of each |
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individual file available for the extraction along with a lin k to download that file |
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are provided. Perhaps one of the most important features of t he web interface |
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is the interactive plotting of individual or combined spect ra directly on the site. |
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This is implemented server side by taking the POST request fo r plotting param- |
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eters along with a unique file name, creating a small script of the commands for |
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loading data and plotting, and piping this script into an ISI S process. Malicious |
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useisprevented by checking all parameter inputsfor approp riatevalues, running |
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the ISIS process as an unprivileged user, and checking the te mp file name for |
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validity before piping. Since the file name is known at the tim e of the request, |
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the page simply needs to reload to show the new plot. The comma nds, any error |
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output, and an ASCII dump of the plot data are available for do wnload as well. |
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Virtual Observatory: TGCatis a registered VO service providing both |
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the Simple Cone Search5and Simple Image Access6Protocols. These are both |
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implemented as an XML output plug-ins taking input from a php script that |
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provides appropriate GET parameters, then creates a query o bject after parsing |
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the input data, finally running the query in exactly the same w ay as for the web |
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and ASCII interfaces. Error handling is done by the calling s cript and meta |
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data is provided by running a query with parameters known to h ave no catalog |
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entries ( indexed ID=0 ). VO queries, and any other type, can b e tracked in |
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the query table using the type column. In this way we can track statistics on |
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requests coming from services such as datascope7. |
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Data Package Downloads: Generally, users will want to download more |
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than one file at a time for analysis, such as such as spectra and responses or |
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productsfrom multiple extractions of the same target. To th is endTGCatruns |
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apackager processthatparsesaqueuetablemuchlikethepro cessingqueuetable |
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described above. Requested packages are added to the packag e queue table, |
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validated and read by the packager which then fetches data to a temp space |
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placing them in a directory hierarchy tagged with ObsID and TGCatID. The |
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entire hierarchy is then tarred, compressed and provided to the user along with |
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file checksums via HTTP. |
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Acknowledgements. We would like to thank Dan Dewey for extensive input |
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on data organization and interface layout, and Mike Nowak fo r ISIS plotting |
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routines and advice on the interactive plotting interface. This work is supported |
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4http://tgcat.mit.edu |
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5http://tgcat.mit.edu/tgCli.php?OUTPUT=V |
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6http://tgcat.mit.edu/tgSia.php |
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7http://heasarc.gsfc.nasa.gov/cgi-bin/vo/datascope/i nit.plTGCat 5 |
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by the Chandra X-ray Center (CXC) NASA contract NAS8-03060. DPH was |
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supportedby NASA through the Smithsonian Astrophysical Ob servatory (SAO) |
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contract SV3-73016 for the Chandra X-Ray Center and Science Instruments. |
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References |
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Huenemoerder, et. al. 2010, ( in preparation ) |
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Houck, J. C., Denicola, L. A. 2000, in ASP Conf. Ser. 216, ADASS IX, ed. N. Manset, |
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C. Veillet, & D. Crabtree (San Francisco: ASP), 591 |
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Williams, Roy, Hanisch, Robert, Szalay, Alex, Plante, Ray 2009, Simple Cone Search |
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Version1.03,http://www.ivoa.net/Documents/REC/DAL/ConeSea rch-20080222.html |
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Tody, Doug & Plante, Ray 2009, Simple Image Access Specification Ve rsion 1.0, |
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http://www.ivoa.net/Documents/SIA/20091008/PR-SIA-1.0-20 091008.html |