Call for Global VLBI Proposals at 3mm wavelength

Deadlines each year:
February 1st and October 1st

We announce the opportunity for coordinated, high angular resolution and high sensitivity GLOBAL VLBI observations in the 3mm band ($85 - 95$ 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 (propvlbi@mpifr-bonn.mpg.de) AND to the VLBA (propsoc$@$nrao.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:

Technical Guidelines for Global VLBI Observations

Main purpose of Global 3mm-VLBI observations:

To image compact radio sources with high angular resolution (up to $50\; \mu$arcsec) and better sensitivity than the stand-alone VLBA can provide. Typical single baseline detection thresholds: $0.06 - 0.4$ Jy (see Antenna Characteristics and Sensitivities).

Observing dates:
Twice per year, in spring (April/May) and autumn (October).

How to propose:

For Global 3mm-VLBI observing proposals have to be submitted electronically to the European mm-VLBI Scheduler, R. Porcas (propvlbi$@$mpifr-bonn.mpg.de) AND in parallel also to the VLBA (propsoc$@$nrao.edu). The submission deadline for observations in the spring is October 1st, and for observations in the fall is February 1st.

Proposers should use the standard VLBI cover sheet. Proposals will be reviewed by NRAO and the participating European Observatories.

Participating Stations:

• in Europe: Effelsberg (100m (Ef)), Onsala (20m (On)), Pico Veleta (30m (Pv)), Plateau de Bure (6x15m, phased (Pb)), Metsähovi (14m (Mh))
• in the USA: VLBA (8x25m) - BR, NL, PT, LA, FD, KP, OV, MK (HN, SC are not equipped with 3mm receivers)
• other stations: as other stations become available in the future, they may join in (next candidates: Yebes (40m), Noto (32m), GBT (100m))

Frequency:

The standard frequency for continuum observations is 86.2 GHz.
For spectral line observations a range of 84-95 GHz is available at Ef, Pv, Pb. The VLBA at present supports 80-96 GHz (NL, PT, FD, KP, OV, MK) except for the stations LA and BR which at the moment only support 80-90 GHz. Thus for the global 3mm VLBI array the common frequency range at the moment is 84-90 GHz. If other frequency setup than standard is needed, the P.I. is asked to contact the European Schedule Coordinator before proposing.

Recording:

All stations: can do MKV/VLBA recording modes with up to 512 Mbps (the standard for continuum observations is currently 512 Mbps)
European stations: can do MKV recording at up to 1 Gbps on special request

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.

Correlation:

The data will be correlated at the MPIfR-VLBI correlator in Bonn (Germany).

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.

Spectral lines:

Allowed number of lags must be within Bonn-correlator limits (for details see: http://www.mpifr-bonn.mpg.de/EVN/MK4CORstatus)

Disk usage:

A limited number of MarkV disks is available, which have to be correlated and released between two adjacent observing sessions (Spring/Autumn). In standard observing mode (512 Mbps) this corresponds to a duty cycle of 0.5 (an equivalent to 12 hours recording every 24 hours). This is a bit more than double the duty cycle offered by the VLBA alone at 86 GHz (where the equivalent of 2-tapes-per-day guideline applies).

Polarisation:

Dual polarisation receivers available at: Ef, Pv, Pb, Mh, VLBA ; single polarisation receivers available at: ON

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.

Sunavoidance:

A 35 degree limit must be obeyed at Pb.

Pointing/Calibration:

mm-VLBI requires special efforts with regard to antenna pointing and data calibration. To ensure the success of the observations several 'rules' must be obeyed:

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.

Scheduling:

For logistical reasons and to ensure optimum use of telescope time, all experiments which got observing time will be scheduled within a block schedule, which is optimized by the Schedule Maker (Thomas Krichbaum). The Schedule Maker will take care of the special needs with regard to antenna pointing, calibration and disk usage.

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:

• R. Porcas (Schedule Coordinator),
• T. Krichbaum (Schedule Maker),
• D. Graham (frequency setup),
• W. Alef (Correlation).

The MPIfR VLBI team