The Virtual Observatory (VO) projects are creating standards to facilitate the discovery and joining of data among astronomical archives. These projects include the US-Virtual Observatory (NVO) which is a member of the International Virtual Observatory Alliance. MAST is working to make its data compliant with the current VO standards. We are currently making our holdings available using VO-defined protocols and standards including those listed below.

• All MAST mission searches returned in the VOTable format.
• MAST implemented the VO Simple Cone Search protocol.
• HST previews are available via the VO Simple Image Access Protocol (SIAP).
• UIT image and preview data are available via SIAP.
• GOODS Version 1 High-Level Science Products (HLSP) are available via SIAP.
• A wide variety of webservices for the GALEX mission will soon be available.
  • GALEX image and spectral previews will be available via SIAP and the Simple Spectral Access Protocol (SSAP) respectively. (The SSAP is not yet fully defined so this will be a prototype).
  • Provide GALEX spectral services to allow users to produce mean, average, etc. GALEX spectra of objects observed in different visits.
  • GALEX will become part of a larger ensemble of surveys and mission under new initiative called SkyNode, the next step in the pursuit of a distributed astronomical query system called SkyQuery.
  • The GALEX GMAX application will return results in VOTable format. GMAX is a positional cross correlation tool.
  • GALEX HTM Footprint service will return results in VOTable format. GALEX users will be able to retrieve data for a single object or for objects which lie within the footprint of any MAST survey or instrument.
• See the MAST Services page for details on what services are currently available and what parameters are allowed.

MAST has begun to integrate some VO services and tools into the MAST website and applications.

• Users may now search the entire set of 4,000 VizieR catalogs and cross correlate the results with any MAST mission. This uses a VizieR web service which communicates using the VOTable standard.
• Users may plot search results from any MAST mission or VizieR catalog search with the new JAVA-based graphical display tool called VOPlot.

Links to useful services already developed by VO.

• VO DataScope Data Inventory Service - MAST holdings can now be searched simultaneously with data from many other surveys and missions through this service developed for the National Virtual Observatory and hosted at HEASARC. The survey and mission data accessed include SDSS, 2MASS, RASS, HST, Chandra and EGRET.
• Main VO Registry Page - This is a fully functional VO registry service. A VO registry service contains a collection of services available to the community for use in building applications. As an example, the Data Inventory Service, (see above), probes this registry to get relevant data. Thus, when a new data service is created and published in the Registry, that service is immediately visible to the scientific community via VO DataScope Data Inventory Service