September 13, 2004NVO Summer School 1

Exploring VO Registries,Resources and Software withThe NVO DataScope and Other VO Tools

Tom McGlynnNASA/GSFC

THE US NATIONAL VIRTUAL OBSERVATORY

September 13, 2004NVO Summer School 2

Summary

• Discovery– Using the DataScope– Types of data resources and major sites– Browsing the data

• Access– How do we get it– Protocols

• Analysis– How do we use data– What programs are available– Standardized formats

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What do astronomers want?

• Information on a particular source or sources– Is this candidate source object for a GRB extended? Could

the X-ray flux for this source have background contamination? What is the radio flux of this source? Are there any nearby SNRs?

• Information on a class of sources– Which of these are QSOs? What is the average X-ray flux

of the B-stars in the sample?• Analysis of a given sample

– Which of these stars have a common proper motion? How does a principal components analysis break down the sample?

• Analysis of correlated data– What are the brightest objects in the SDSS that do not show

up in 2MASS (or vice versa)? Is there a statistical excess of IR flux at the positions of this sample of X-ray sources?

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Resource Discovery

• Do you know if data is available?• Are there resources in addition to the

ones you know about?• How do we select among multiple

resources?

VO registries are appropriate for answering these kinds of questions.

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Starting the DataScope

• The NVO DataScope uses the VO registry to search for existing data at many sites.– Finds out what resources might be appropriate– Queries them– Organizes the results

Start the DataScope

Look at:• A well studied source: 3C 273• A much less observed source: the last BATSE gamma-ray

burst with RA/Dec of 06 40 55 -04 48.5

The DataScope caches information, so we can reuse the results from the last time someone tried this query.

Only required field

User can select type of resources to be displayed.

Starting the

DataScope

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What do we get?

• Cone searches – queries of positional catalogs• Simple Image access – queries of archives of images or image generation services

• Some prominent resources:– NED: extracts information about extragalactic sources from the literature and publshed catalogs. Images

are available as an SIA service and data about each source can be extracted using as a VOTable.– SIMBAD: Similar to NED but covering all objects.– ADS: links to astronomical literature. The ADS provides a pseudo-conesearch which gives articles that are

related to given areas on the sky.– VizieR: the basic reference resource for thousands of astronomical catalogs mostly describing objects. The

registry currently only has a few of the many catalogs in VizieR.– NASA Domain Archives:

• IR: IPAC provides image and cone search data for 2MASS and space based IR missions.• Optical/UV: MAST provides image services for the DSS1 and 2 and cone search capabilities for the datasets archived in

MAST. Most (all?) cone searches are linked to preview and/or archival data.• High-energy: The HEASARC provides cone search services for its archive holdings with links to the data archives. Many

object catalogs are also served with considerable overlap with VizieR.• Microwave: The LAMBDA archive supports MAP and some other microwave datasets but is not yet indexed in the registry

– SkyView: provides an image service which takes existing survey data and resamples and mosaics to get the image specified by the user. All spectral regimes from radio through gamma-ray are supported. SkyView provides an SIA service to its higher resolution datasets.

– SDSS: a large multicolor optical CCD survey of unprecedented depth. Sloan data is avialable through cone and SkyNode services

– GSC2.2/USNO: Deep all sky optical surveys based upon Schmidt plate data. These datasets are available through redundant though not usually mirror cone-search services.

– ADIL: A library of astronomical images from all wavelenths but especially in the radio. Both an image and cone search query is supported.

– CADC: Support for a number of ground and space observatories. Not all CADC datasets are currently available on the Web.

– Mission specific archives: Chandra, XMM, NTT, …

Near 3c273

Starting an uncached query near the last BATSE Burst Trigger

After a minute we have searched about 250 resources in total.

After 3 minutes the search is pretty much done.

There are many fewer observations that for a popular target like 3c273.

Many resources did not return data.

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DataScope results organization

• Image archives (SIAP services)– Organized by wavelength

• Catalogs(cone search)– Queries of catalogs of observations

• Organized by wavelength

– Queries of catalogs of objects• Organized by object type

– Other queries

• Queries that didn’t return information

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Browsing DataScope results

• Find resources that have information• Look at full metadata for resources

– Help documentation• Quick look images

– Look at images in the SIAP results• First image is displayed by default but all quicklook data is accessible.

– Look at catalog results for obervations and objects• Link to archives and ADS

– Click on HST observation link• Click on Data links at the beginning of each line

– Note the HEASARC and MAST IUE links• Only the MAST link points to data since that is the Optical/UV domain archive.

– Click on the ROSPUBLC observations and then on Data to get to the HEASARC archive.

– Click on the ADS link and then on any of the bibcodes– These use non-VO methods to access archives but work is proceeding on

agreeing on standards.

Registry Metadata for the DSS1 SkyView resource

Looking at the SkyView image and Simple Image Access VOTable Response

The GSC2.2 catalog near the last BATSE burst. Only the first few of several thousand rows is shown.

We can send this table directly to VOPlot or VOStat using the links shown

Looking at the actual VOTable.

HUT observations of 3c273. Note the data links.

Following the data links to the MAST preview pages.

Now searching the ADS for papers with targets near 3c273. Note the bibcode links.

Following the bibcode links to the ADS.

Color-Color plot of 2MASS sources near 3c273 using VOPlot

VOStat linear regression on magnitudes of 2MASS sources

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Some concerns

• Duplicate resources– HEASARC and MAST IUE catalogs– Multiple USNO catalogs– ADIL as SIAP and Cone search

• Obsolete and superseded resources• Too many resources?

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Getting the data

• Three major VO protocols…– Cone search

• CGI simple positional query with VOTable result

– Simple Image (Spectral) Access• CGI initial query gives VOTable with URLs listing

available datasets (data likely to be in FITS)

– SkyNode• SOAP VOQL (SQL-like) query with SOAP response.

Not used in DataScope (yet!)

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Access using DataScope

VOTable and FITS data may be retrieved or sent to analysis tools

• Select resources by clicking on appropriate checkboxes.– Go into SIA (SSA) resources with multiple entries to select desired

observations.– Select catalog queries or single element SIA (SSA) resources using top-

level checkbox

• To download resources click on ‘TAR selected resources’ ….– All resources are combined into a single tar file.

• … or send the data directly to Aladin or OASIS– May be limits on the number of datasets that can be sent

• Individual VOTables can be sent to VOPlot or VOStat

• Need to make more analysis tools available

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Data Analysis

Successful data analysis requires agreed standards for the meaning of the data.

• FITS WCS for image data• VOTables with UCDs• VOQL results• Discipline standards (optical, IR, x-ray)• UCDs may address this at lowest level.Probably the hardest part of the VO.

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Image analysis using Aladin

• Select a few images and object catalogs and Start Aladin.

• Image overlays• Object identification• Guide stars• Catalog cross-correlation

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Image analysis using OASIS

• Similar to Aladin

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Using fv and DS9

• Data can easily be used in local software tools

• By setting appropriate handlers for FITS data, FITS viewers may be invoked automatically

Downloading a FITS file from NED into fv

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Conclusions

• DataScope illustrates access to myriad VO-enabled data resources

• VO doesn’t replace existing systems, it enhances their grasp and availability.

• There is a long way to go yet