Facilitating regular Global VLBI Observations at 3mm

Final Version (28.8.2003)

There is considerable scientific interest for global VLBI observationsin the 3mm-band. Since the CMVA has ceased organizing such experiments, there is at present no possibility to propose and perform global  3mm-VLBI observing.

With the two IRAM telescopes (the phased 6-element interferometer on Plateau de Bure and the 30m telescope on Pico Veleta), the OSO 20m radio telescope at Onsala, and the MPIfR 100m telescope in Effelsberg, the sensitivity of 3mm VLBI will be enhanced by at least a factor of 3-4 compared to the stand-alone VLBA. The combination of the existing mm-VLBI telescopes in Europe (MPIfR, IRAM, Onsala, Metsahovi - other telescopes may join in as they become available for VLBI) with the VLBA and the GBT (and later with the LMT, CARMA, ALMA) will create a large and sensitive 3mm-VLBI network. This Global 3mm-VLBI network can provide high angular resolution (up to 50 micro-arcseconds) and high dynamic range (of a few hundred) images of compact radio sources of a much better quality than before.

In order to make regular 3mm-VLBI observing possible on a basis which is open to the astronomical community and which allows - despite the technical difficulties at each telescope - successful absentee observing, the participating observatories and institutions agree (see the Memorandum of Understanding, CLICK HERE):

1)To perform coordinated global VLBI observing, combining the European and American telescopes on a regular basis.
2)For logistical reasons, "dynamic scheduling" (as used for most VLBA observations) is not at present possible for the global 3mm-array. Therefore two global 3mm observing sessions per year at roughly 6 month intervals will be set up. To facilitate scheduling, the observing dates will be fixed and frozen at least 6-12 months in advance. Each observing session will last up to a maximum of 5 days. The actual time scheduled for each session, will be based on proposal pressure and on the evaluation of the proposals' merit by the review process in place for the participating observatories.
3)A regular Announcement of Opportunity for Global 3mm-VLBI will be made to the community twice per year, for proposal deadlines coinciding with the normal VLBI/VLBA ones (e.g. February 1st for a session in autumn (September-November), and August 1st for a session in spring (March-May) of each year). Information regarding the 3mm VLBI capabilities of the network and advice for proposers are available on the web (see http://www3.mpifr-bonn.mpg.de/div/vlbi/globalmm). Proposals asking for observing time with the Global 3mm-VLBI array should be sent initially to the NRAO using their Proposal Submission Tool (PST). From proposals will be send to the European Schedule Coordinator. He will forward the proposals within Europe to the participating European observatories.
4)Each observatory decides how it would like the VLBI proposals to be refereed. Observatories may use their existing refereeing systems or designate one or more individual scientists as special referees for rating the proposals or just join the refereeing from other observatories. Each observatory will provide the results of its review process to the Schedulers no later than 12 weeks after the proposal deadline.
5)Similar to the tried and trusted scheme used for Global cm-VLBI, a two person scheduling committee (SC), consisting of a European and a VLBA scheduler, will allocate observing time for each proposal on the basis of the proposal ratings received from the observatories. The NRAO uses their present VLBA referees and consolidate their views in its own Scheduling Committee. The European Scheduler Coordinator consolidates the proposal ratings received from the European mm-observatories. The SC combines all ratings and schedules projects along the lines of present Global cm-VLBI. (In the event of unresolvable disputes, matters will be referred to the Directors of the participating institutes.) The SC will inform the users of their proposal ratings, the amount of observing time allocated and any observing mode restrictions. The SC will also generate a block schedule, scheduling the allocated proposals within the observing sessions, and will distribute this to the observatories and P.Is. After being reviewed, each successful proposal is eligible for scheduling for a 1 year period (i.e. can be scheduled in the next session or the session thereafter), after which it must be re-proposed, if the proposer still desires observing time. If an observation fails a proposal's eligibility may be prolongued by ONE session (see note B).
6)All experiments are grouped together and are observed within one or a few block schedules, which are made by the "Schedule Maker" on the basis of the time allocation made by the SC. If the P.I. wants to actively participate in the scheduling process, he must provide a schedule in NRAO-SCHED format (key-file), which the "Schedule Maker" will incorporate in the block schedule. Although any of the "validated VLBA observing modes", which are allowed by the SCHED programme in principle are possible, mainly standard and in previous 3mm sessions well tested observing modes will be used. See also note A below and the Technical Guidelines.
7)MPIfR offers to correlate the data at its correlator center in Bonn and provide the data to the P.I. in UV-FITS format. (Use of other correlators might be desireable for a few experiments, if there are good technical reasons for it.) The proposers have exclusive use of the data for a proprietary period of 12 months after completion of correlation. MPIfR will release the recorded disks after correlation within ~4 months, so that the limited pool can be re-distributed to the observatories for the next session.
8) Availability of recording media (disks) may lead to a limitation of the recording cycle which can be used in a session. For a recording rate of 2 Gbps, a duty cycle of 0.5 is envisaged, but cannot be guaranteed. The available disks come from a pool maintained at the MPIfR.
A. Integrated observing schedules have advantages for making more efficient use of the available observing time. An experienced mm-VLBI observer will be designated "Schedule Maker" to ensure that the schedule is suitable for all observatories, where possible to share calibration observations and techniques, or to assist in making individual schedules. The individual project key-files should be sent to the "Schedule Maker" 4 weeks before the observing session. The "Schedule Maker" will send final key-files to the NRAO 2 weeks before the observing session. A few days later, after check with NRAO staff, the schedule will be finalized and distributed to the participating observatories.
B. Millimeter-VLBI observations are especially vulnerable to bad weather conditions, which may result in the need for reobservation. If, before correlation, the P.I. and correlator staff judge that the data obtainable will not permit the scientific aim of the proposal to be met (e.g. not enough sensitivity due to loss of large antennas), the P.I. can ask the SC for ONE reobservation in the next possible session and the observations will not be correlated. The proposal's eligibility will then be prolongued by ONE session. Scheduling in the next session will depend on the competition from other eligible proposals. A proposal may not be prolongued a second time. It must be resubmitted for a new review.

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