We announce the opportunity for coordinated, high angular resolution and high sensitivity GLOBAL VLBI observations in the 3mm band ( GHz), complementing stand-alone VLBA observations at this frequency.
The Global 3mm VLBI Array consists of 8 VLBA antennas equipped with 3mm receivers, plus the IRAM 30m telescope on Pico Veleta (Spain), the phased 6-element IRAM interferometer on Plateau de Bure (France), the MPIfR 100m radio telescope in Effelsberg (Germany), the OSO 20m radio telescope at Onsala (Sweden), and the 14m telescope in Metsähovi (Finland).
The Global 3mm VLBI Array is the successor to the former Coordinated Millimeter VLBI Array (CMVA) and offers 3 to 4 times more sensitivity than the stand-alone VLBA (although for logistical reasons this global array cannot be ``dynamically'' scheduled). Observations with the Global 3mm VLBI array will be scheduled in time blocks in special observing sessions, performed twice per year, typically in mid May and mid October. The actual duration of each session depends on proposal pressure and typically ranges between 3 and 5 days.
The Global 3mm VLBI Array supports the same observing modes as the VLBA. Note that 512 Mb/s recording is offered as a standard mode for continuum observations in order to maximize the sensitivity. Correlation will we performed in absentia at the MPIfR MK4 correlator in Bonn unless some technical reason for using another correlator is given in the proposal. The P.I. will receive the correlated data in uv-fits format.
For each session proposers are asked to submit their proposals to both the European mm-VLBI Scheduler, R. Porcas (firstname.lastname@example.org) AND to the VLBA (propsocnrao.edu) for the normal VLBI deadlines: October 1st for observations in spring and February 1st for observations in autumn of each year. Proposers should use the standard VLBI cover sheet (from the VLBA web site). Proposals will be reviewed by NRAO and the participating European Observatories.
Global VLBI observations at 3mm are subject to some technical restrictions, which are summarized in the technical guidelines below:
Twice per year, in spring (April/May) and autumn (October).
Proposers should use the standard VLBI cover sheet. Proposals will be reviewed by NRAO and the participating European Observatories.
Note: The VLBA will support only its ``Validated Observing Modes'', which are the modes supported by the NRAO-Sched programme.
For continuum observations the recommended standard recording mode is 512-8-2 (512 Mbps, 16 IFs of 8 MHz bandwidth each, 2 bit sampling in left circular polarisation (LCP) or 8 IFs of 8 MHz bandwidth each, 2 bit sampling in both left and right circular polarisation (LCP and RCP). P.I's who wish to record with 1 bit sampling or with modes not compatible with 512-8-2 should justify this in their proposal and contact the Schedule Maker in order to make sure that their prefered recording mode is possible.
After correlation the data will be made available to the P.I. in UV-FITS format, compatible to be read in into the most recent version of AIPS.
Note: At present it is not yet possible to reduce polarization data recorded at PV in AIPS, due to the special mount-type of the PV antenna (Nasmyth focus). An installion of a new AIPS TST version which can deal with Nasmyth mounted telescopes (kindly provided by R. Dodson) will be available soon. The receivers of PdB have been upgraded recently and now provide dual polarisation (LCP/RCP). However for PdB, the calibration for this observing mode is not yet well tested. Test reports from users, willing to help to characterize the station D-terms are welcome.
For large antennas like Pv, Ef, Pb frequent (3-4 times per hour) pointing and calibration gaps of at least 5-7 min duration must be scheduled between VLBI scans. Pv and Ef will use these pointing scans also for antenna temperature measurements. The PdB-interferometer additionally needs to do the phasing during these gaps.
For the VLBA the pointing is done quasi-automatically on bright SiO-maser sources at 43 GHz. The VLBI schedule (key-file) must contain ``reference pointing scans'', which are scheduled between adjacent VLBI scans. The pointing gaps need a length of at least 3 min duration.
For continuum imaging the following well tested observing scheme will be used at 512 Mbps: 4 VLBI scans per hour, one every 15 mins, with pointing gaps between adjacent VLBI scans
P.I.'s who wish to deviate from this standard should indicate this in the proposal and should contact the Schedule Coordinator or the Schedule Maker to check whether this is possible.
P.I.'s who wish to participate actively in the scheduling process should indicate this in their proposal. They will contacted by the Schedule Maker during the scheduling process.
The observing schedules (key-files) will made in week 4 and 3 before observing. In week 2 before observing they will be send to the VLBA, where a final check is done. The individual stations fetch the final schedules from the usual '/astronomy' account (http://www.vlba.nrao.edu/astro/VOBS/astronomy/) via ftp during week 1 before observing.
In case of technical questions please contact the following
persons at MPIfR Bonn, Germany: