TGCat : The Chandra Transmission Gratings Catalog and Archive
The newly released Chandra Transmission Grating Catalog and Archive, TGCat, presents a fully dynamic online catalog allowing users to browse andcategorize Chandra gratings observations quickly and easily, generate custom plots of resulting response corrected spectra online without the need for special
software and to download analysis ready products from multiple observations in one convenient operation. TGCat has been designed to take advantage of theconvenience and power of modern browsers and servers to not only enrich the features available but also provide better access to helpful resources relating tosearches and returned values. TGCat has been registered as a VO resource with the NVO providing direct access to the catalogs interface. Currently underdevelopment are Simple Cone Search and a Simple Image Access interfaces compliant with NVO standards and we intend to provide spectra via the Simple
Spectral Access protocol. The catalog is supported by a back­end designed to automatically fetch newly public data, process , archive and catalog them, At thesame time utilizing an advanced queue system integrated into the archive's MySQL database allowing large processing projects including reprocessing, several
planned feature additions, and the event of catastrophic data loss, to take advantage of an unlimited number of CPUs across a network. A unique feature of thecatalog is that all of the high level functions used to retrieve inputs from the Chandra archive and to generate the final data products are available to the user inan S­Lang written library with detailed documentation. Here we present a structural overview of the Systems, Design, and Accessibility features of the catalog
and archiveSystems, Design and Accessibility
1

Arik W Mitschang
2
David P Heunemoerder
1
Joy S Nichols
1. Smithsonian Astrophysical Observatory
2. MIT Kavli Institute for Space ResearchInternal web based VV
interface.
Change queue parameters forcustom extractions, e.g. Mask
widths, Zero order positions,
etc...

New publicgratings
observations

Outside WorldTGCat Queuetgcat.mit.edu

Chandra Data
Archive

External MySQL database, File Archive
and Apaceh2/php Web Server

Validation And
Verification (V&V)

Serendipitous source
detection

Plannedfeatureaddition

Target Zero Order
determination
Combinedproducts

Indevelopment

Processing ( S-Lang freely
available functions )TGCat processing daemons, unlimited number of network
attached CPU's can request work from the queue

Notifications

in order to maintain a level ofsecurity on the internal network
where processing takes place, theworld connected web server has
limited access to internal MIT
machines. Thus, the database andarchive get dumped nightly to theweb server. A resultant benefit isan extra layer of database andarchive backup

TGCat database andarchive-meta-data-derived spectral
properties-file based extraction
products-preview images

Automatic Nightly

MIT Internal

Database and filearchive get sync'ed intheir entirety everynight. ( scp amysqldump of tables
to web/mysql server,
rsync archivedirectories)

USER-optional email notification-download tar'ed gzip'ed data
packages via
httpPackager

Query Table

Packaging Queue

Team members get notified automaticallyof new data awaiting V&V

Simple Image Access Protocol (SIA)
http://tgcat.mit.edu/tgSia.php?POS=ra,dec&Simple Cone Search Protocol (SCS)
http://tgcat.mit.edu/tgCli.php?RA=&DEC=&SEP=&VERB=VO Interface

All Queries are logged andstored in a MySQL table forlater use and statistics
gathering. Type and origin
meta-data are saved. Query
table records indexed rows of
resultant records, greatly
improving performance andscalability. Row sub selections,displayed columns, and usertags are among the data saved
to simplify and speed requerying

Web Interface
Standards Compliant NVO resources

Users can viewquery
results in ASCII,HTML and VOTable(XML) format

VO Table
VirtualObservatory

Example NVO DataScope cone search output ( actually
linked from the web interface's source table view ),showing resultant image access through TGCat SIA
Data products associated with SIA are:
The level 2 event file created in processing●Full field summary image showing zero order positionand gratings arm locations●Link to the web interface extraction summary page
●TGCat treats VO queries thesame as any other, using thesame query table interface, only
returning a VOTable XML file as
opposed to HTML/ASCII output.
In fact, the VOTable output is
not limited to queries using theVO standard interfaces
provided by TGCat, VOTable
output may be generated forany query for use with VO
software and data viewers( such as Alladin )The web interface
takes advantage ofJavascript andCookies whereavailable to increase
usefulness, but makeno dependencies on
suchAccess links.
Suchas SIMBAD,
DataScope,
ADS
abstract,...