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22 Feb 2006STScI 1

Working with the Virtual ObservatorySession 1: Introduction andScience Motivation, Part 1

The Virtual Observatory is a frameworkthat enables new astronomical

research by greatly enhancing access to worldwide data and computing resources.

THE US NATIONAL VIRTUAL OBSERVATORY

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Threads of the the VO Fabric

Multiwavelengthastrophysics

Archival Research

Survey astronomy

Temporal astronomy

NGC3104

Moore’s Law

Dig

ital detecto

rs

The In

ternet

Data Stan

dard

s

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NVO Applications

• Registry Interface• DataScope• Coverage Maps• Open SkyQuery• WESIX (SExtractor)• WCS Fixer• Spectrum Services• VOEvent Net• Montage mosaics• Integration with legacy software systems

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NVO Registry Portal

Find source catalogs, image archives, and otherastronomical resources registered with the NVO

A Registry is a distributed database ofVirtual Observatory resources:primarily access services for catalog,image, and spectral data, but alsodescriptions of organizations and datacollections. There are severalcoordinated registry implementationsthat share information by harvestingeach other's resources. This registry isat STScI in Baltimore, MD.Searches for resources can be done by keyword, or advanced queries can beexpressed in the SQL language. The registry is open for humans through webforms, or machines through SOAP web services.

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DataScope

Using the NVO DataScope scientists candiscover and explore hundreds of dataresources available in the VirtualObservatory. DataScope uses the VOregistry and VO access protocols to link toarchives and catalogs around the world.Users can immediately discover what isknown about a given region of the sky: theycan view survey images from the radiothrough the X-ray, explore archivedobservations from multiple archives, findrecent articles describing analysis of data inthe region, find known interesting or peculiar

Discover and explore data in the Virtual Observatory

objects and survey datasets that cover the region. A summary page provides a quickprécis of all of the available data. Users can download images and tables for furtheranalysis on their local machines, or they can go directly to a growing set of VOenabled analysis tools, including Aladin, OASIS, VOPlot and VOStat.

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Open SkyQuery

Cross-match your data with numerous catalogs

OpenSkyQuery allowsyou to cross-matchastronomical catalogsand select subsets ofcatalogs with a generaland powerful querylanguage. You can alsoimport a personal catalogof objects and cross-match it against selecteddatabases.

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Spectrum Services

Search, plot, and retrieve SDSS, 2dF, and other spectraThe Spectrum Services web site isdedicated to spectrum related VOservices. On this site you will findtools and tutorials on how to accessclose to 500,000 spectra from theSloan Digital Sky Survey (SDSS DR1)and the 2 degree Field redshift survey(2dFGRS). The services are open toeveryone to publish their own spectrain the same framework. Reading thetutorials on XML Web Services, youcan learn how to integrate the 45 GBspectrum and passband databasewith your programs with few lines ofcode.

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Web Enabled Source Identificationwith Cross-Matching (WESIX)

Upload images to SExtractor and cross-correlate theobjects found with selected survey catalogs.

This NVO service does sourceextraction and cross-matchingfor any astrometric FITS image.The user uploads a FITSimage, and the remote serviceruns the SExtractor software forsource extraction. Theresulting catalog can be cross-matched with any of severalmajor surveys, and the resultsreturned as a VOTable. Theweb page also allows use ofAladin or VOPlot to visualizeresults.

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22 Feb 2006STScI 9

Coverage Maps

The NVO Sky StatisticsService generates sourcecounts, coverage maps, andlinks to downloadable datafor catalog holdingsavailable through the NVOprotocols, including IRSA,NED and CDS VizieR

View catalogcoverage mapsand sourceinventories for aposition or objectof interest.

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WCS Fixer

Repair image coordinates in images with inaccurate ormisaligned coordinate systems.

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22 Feb 2006STScI 11

VOEvent NetExplore the multiwavelength sky inthe vicinity of transient events.

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Montage Mosaics

Make mosaicsfrom 2MASS,DPOSS, orSDSS images.

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VO Tools

• VOTable display and analysis– VOPlot, Topcat, Mirage

• Image display and analysis– Aladin, OASIS– Other standard display tools for downloaded data

• Spectrum display and analysis– VOSpec, SpecView

• Time series treated like spectra

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Interoperability

VizieR: Contains morethan 4000 astronomicalcatalogues consisting ofone or several tables.

Problem: as the catalogues come frommany different sources, the originaldescriptions are very heterogeneous:“Give me all tables containing the Vmagnitude in the Johnson system.”144 different names for Johnson V.

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Interoperability challenges

• Metadata standards• Data discovery• Data requests• Data delivery• Units• Database queries• Distributed applications; web services• Authentication and authorization

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NVO Components

• Data discovery and location– Resource Registry: Organizations, archives, tables, databases,

services– Footprint Services

• Data access– Simple tables and observation logs: Cone Search– Images: Simple Image Access Protocol (SIAP)– Spectra: Simple Spectrum Access Protocol (SSAP)VOTables and FITS used to exchange data throughout the VO– Databases: SkyNode, with Astronomical Data Query Language

(ADQL)– Transient events: VOEvent protocol– Data models, Space-Time Coordinates (STC)

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NVO Components

• Distributed data storage– VOStore, VOSpace– Authentication and authorization

• Distributed computing– Web services– Grid services– Scalability

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To get started…

http://us-vo.org