Observing Program

IYA09 Very Large Astrometry Session

International Year of Astronomy 2009 Very Large Astrometry Session

Purpose    Goals    Observation Period Network Resources    Schedule Documents    Links

(Please send a message to the Coordinating Center if you have updates or links to be included on this page.)

Purpose

As an activity for the International Year of Astronomy (IYA2009) the IVS is organizing a special astrometric session with as large a participation as possible. The observing goal is to observe as many of the 295 ICRF2 defining sources in a single 24-hour session as possible (the southern sky may not be fully covered) avoiding possible systematic effects of patchwise observing. The IYA09 session will thus enable a fully connected control of the ICRF2 and constitutes an ideal kick-off session for ICRF2 monitoring. The session will be accompanied by outreach activities at the stations and other sites. Bordeaux Observatory hosts the dynamic Web page IYA 2009: VLBI Astrometric Session which will depict the latest images available for each source (either from BVID, RRFID, or VCS) and will be updated every time a new source is observed.

Goals

The very large astrometry session for the IYA2009 is an unprecedented effort to acquire unified data on the ICRF2 defining sources and gives the general public the opportunity to bear witness to the observational part as it happens.

• Science: One of the major deficiencies of the VLBI data set for all-sky astrometry is that the usual 24-hour sessions observe only a small part of the total VLBI source catalogue. The primary reason is that the most common sessions are for monitoring EOP and use the small geodetic source catalogue. The earliest VLBI sessions were limited to 12–15 sources, but the number of sources gradually increased with time. A typical modern session observes 50–70 sources.
  
  Most sources in the complete catalogue, including many of the ICRF2 defining sources, have usually been observed in a limited set of sessions specifically for the maintenance and improvement of the celestial reference frame. The complete catalogue is the result of concatenating all the relevant observations, both geodetic and astrometric. However, the strength of the overall network of sources in the sky depends on the overlap of common sources from session to session. Sources observed in a session that had no common sources with any other session could not be related in position to the other sources without using external information. Because of the nature of scheduling VLBI observations and the differences between the station networks used for various purposes, the source overlap between sessions is largely random and includes only a small fraction of the sources in the sessions. The weakness of overlapping is a particular difficulty linking the northern and southern sky hemispheres because of the small number of southern VLBI stations and limitations on observing time.
  
  In contrast, this IYA09 astrometry session will attempt to observe all the ICRF2 defining sources (see sky map) and provide the arc lengths between all sources without relying on source overlaps. This should give much stronger geometry and relative positions between the ICRF2 defining sources. Unfortunately there are a few practical and exceptional difficulties. The ICRF2 defining sources are evenly distributed on the sky, so a few sources will be too close to the sun for good dual frequency observations. The station network in the southern hemisphere is sparse and generally insensitive. Three stations are smaller than the 20-m size common in the geodetic network. In addition, a key station in South Africa is under repair and is unable to participate. It is likely that more southern sources will be missed than is desirable. Nonetheless this is an exceptional opportunity to strengthen the ICRF2.
  
  
  
• Outreach activities: An important goal of the IYA09 session is to reach out to the public. This is in line with one of the major goals of the the IYA, which is aiming at stimulating worldwide interest in astronomy and science under the central theme "The Universe, Yours to Discover". The IYA2009 events and activities promote a greater appreciation of the inspirational aspects of astronomy that embody an invaluable shared resource for all nations (see http://www.astronomy2009.org/).
  
  The IYA09 session is an official event of the IYA and is announced on the IYA 2009 Web site. News updates were posted on November 9 and November 10. A dynamic Web page is hosted at Bordeaux Observatory. This page provides the latest images available for each source (either from BVID, RRFID, or VCS) and will be updated every time a new source is observed. It will also provide links to Web cams of participating stations that have this capability. All information regarding the IYA09 session such as articles, interviews, and the like, will be collected and provided through this Web page.
  
  For the stations, a special issue of the IVS Newsletter is under preparation. The issue will give an overview of "VLBI through the Decades" from the first VLBI experiments, to first operational sessions, to the formation of the IVS, and to the next generation VLBI system and beyond. In addition, a flyer will be prepared showing a map of the actual station network with explanatory text (rationale of session, what is a quasar, etc.) on the back. These two items will be produced as PDF files for the stations to print out (in full color).

Observation Period

The 24-hour observation period is set to:

• observation start: Wednesday November 18, 2009 @ 18:00:00 UT
• observation end: Thursday November 19, 2009 @ 18:00:00 UT

Network Resources

The observational network of the IYA09 session consists of 25 geodetic VLBI stations and the 10 VLBA stations.

The geographical distribution of the entire network is depicted in the network map:

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Schedule

The schedule will be generated using the NASA SKED program at GSFC. Scheduling goals will be to have on average 3 scans per source (most sources with 3–5 scans) and about 100–130 observations per source, sufficient for imaging. We will strive for optimizing the schedule to a maximum number of observations and a reasonable sky coverage at all stations. A limiting factor will be the heterogeneity of the sensitivity of the participating stations whose dish sizes range from 3 m to 100 m.

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Documents

All documentary material pertaining to the IYA09 session is collected here. Please provide the Coordinating Center with articles, interviews, photos, and other items that you consider worthwhile sharing.

• Handout and display material
• Press releases:
  • 10 November 2009: English version, Japanese version
• NASA top news story on ICRF2

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Links

In the following please find a list of relevant links. Please notify the Coordinating Center if you want a link added.

• Dynamic Web page at Bordeaux Observatory: IYA2009: VLBI Astrometric Session
• International Year of Astronomy 2009 Official Web site
• IYA2009 news updates:
  • 9 November 2009: Interferometry super-session to be held for IYA2009
  • 10 November 2009: Thirty-five radio telescopes around the world will conduct an unprecedented observation
  • 18 November 2009: Un projet de radioastronomie unique pour quadriller le ciel avec une précision extrême
• NASA top news story on ICRF2
• News coverage and press releases:
  • Mittelbayerische Zeitung (in German): Ein Experiment der Superlative
  • TU Wien (in German): Experiment der Superlative
  • GSI Press Release (in Japanese): World-size Telescope Conducts Largest Astrometric VLBI Session Ever Observed
  • El País (in Spanish): Récord de radiotelescopios en una macrosesión de astrometría

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