Call for Observing Proposals on the Interferometer

Observing proposals are invited for the IRAM Plateau de Bure Interferometer (PdBI), for the period Nov. 15, 1995 to May 15, 1996. The deadline for applications is September 4th, 1995. The available frequency range will be 82 GHz to 116 GHz for the 3mm band, and initially 210 to 245 GHz for the 1.3 mm band.

Details of the PdBI and the observing procedures are given in the document ``An Introduction to the IRAM Plateau de Bure Interferometer'' (copies can be obtained from the address below, or from Internet via the World-Wide-Web and NCSA-Mosaic software; use IRAM homepage http://iram.fr/iram.html). Proposers should read this document carefully before submitting any proposal.

Proposals should be sent to: IRAM Scientific Secretariat
Interferometer Observing Proposal
300 Rue de la Piscine
F-38406 Saint Martin d'Hères Cedex
FRANCE

IRAM expects to schedule and complete between 20 to 30 projects in this period, with an elapsed time of at least two months between start and end of any given project. Selection will be based on scientific merit, technical feasibility, and adequacy to the instrument.

For this call for proposals, please note the following specificities:

Proposal Category:

This will be the first winter with dual-frequency capability for Plateau de Bure. IRAM wishes to offer to its community immediate access to the new facilities, but given our lack of previous experience, we define 4 strict categories of proposals:

Category 1

: Proposals that ask for 3mm data ONLY.
1.3 mm receivers can still be used to provide either phase stability information or purely qualitative information such as the mere existence of fringes. The maximum available baseline length will be about 300 m.

Category 2

: Proposals that ask for 1.3mm data ONLY.
3mm receivers will be used for pointing and calibration purpose, but cannot provide any imaging. The maximum available baseline length will be about 200 m.

Category 3

: Proposals that ask for dual-frequency observations.
Because of technical limitations, such proposals can only be carried out on COMPACT SOURCES (less than 15).

Category 4

: Exploratory proposals
Proposals whose scientific interest justifies the attempt to use the PdB array beyond its guaranteed capabilities. This category includes for example long baselines observations (A array at 3mm, B array at 1.3mm), non standard frequencies for which tuning cannot be guaranteed, and more generally all non standard observations.

IRAM will provide its usual ``guarantee of completion'' for all projects in the first 3 categories. On the opposite, the 4th category of proposals will NOT benefit of such a guarantee, although IRAM will of course make its best effort to complete them.

The proposal category will have to be specified on the proposal cover sheet (you must use the new form), and should be carefully considered by proposers.

1.3 mm band:

All antennas are now equipped with fully operational dual frequency receivers. Since our knowledge of phase stability at 1.3 mm is based on the extrapolation of 3mm observations over the last years, no real guarantee about 1.3mm performances can be given yet. Note that even the ``compact'' CD array would give a resolution better than 2 at 1.3mm. Therefore, we have added a new configuration called D2, which in combination with the D1 configuration gives a very compact D array.

This array should be well suited for exploratory work at 1.3 mm. Though the ultimate goal of the 1.3 mm band is undoubtedly high resolution, proposers should carefully balance the pro and cons of the various configuration options for this winter.

Note that the field of view at 1.3 mm is very restricted (about 20).

Dual-frequency operation:

The 3mm and 1.3mm receivers are aligned to within about 10. This is probably sufficient for reasonable simultaneous imaging of compact objects (), but not in case of extended structure. In particular, simultaneous dual-frequency imaging of nuclei of galaxies may be seriously affected. See ``Proposal Category'' above.

Configurations:

The baseline extension will be completed this fall. Accordingly, the sets of available configurations have been modified. The configurations now include:

()previously called D
()added to provide 3 at 230 GHz
(*) The details of those configurations are currently being revised to take into account the possibilities offered by the new stations W20, W23, W27 and N30.

The PdB interferometer will thus offer 4 basic arrays:

``High'' resolution mosaicing at 3mm can be performed by combining BC+D1.

Very long baselines: configuration A:

Imaging at 1 resolution cannot be guaranteed for the next session. High resolution work requiring the A1 A2 configurations should preferably focus on size measurements of compact objects. Proposals asking for long baselines should be submitted in ``Category 4''.

Signal to Noise:

The rms noise can be computed from

where

• is the system temperature in scale (120 K below 110 GHz, 250 K at 115 GHz, 500 K at 230 GHz)
• is the Jansky per Kelvin conversion factor (30 at 3mm, 50 at 1.3mm)
• is an efficiency factor due to atmospheric phase noise (0.9 at 3 mm, 0.6 at 1.3 mm)
• is the basic number of configurations (2 for D, 3 for CD, 4 for BC)
• T is the integration time per configuration in seconds (3 to 8 hours, depending on source declination)
• B is the channel bandwidth in Hz (500 MHz for continuum, 40 kHz to 2.5 MHz for spectral line, according to spectral correlator setup)

Receivers:

Below 110 GHz, receivers offer best performances in LSB tuning with high rejection (20 dB): expected system temperatures are (in scale) 100 to 150 K for the winter time. Above 110 GHz, best performances are obtained with USB tuning, low rejection (4 to 6 dB): expected system temperatures are 250 K at 115 GHz. DSB tuning is possible over the whole frequency range, but the system temperature may degrade significantly.

The 1.3 mm receivers give DSB tuning with typical T below 50 K. Expected SSB system temperature are 400 to 500 K. However a relatively narrow resonance significantly degrades the performances near 240 GHz. The guaranteed tuning range is 210-245 GHz, but it may be possible to reach lower frequencies for specific cases. Higher frequencies are unlikely to be feasible this winter because of limitations in the triplers.

Coordinates and Velocities:

The interferometer operates in the J2000.0 system. For best positioning accuracy, source coordinates must be in the J2000.0 system; position errors up to 0.3 may occur otherwise.

Please do not forget to specify LSR velocities for the sources. For pure continuum projects, the ``special'' velocity NULL (no Doppler tracking) can be used.

Coordinates and velocities in the proposal MUST BE CORRECT: A coordinate error is a potential cause for proposal rejection.

Correlator:

The correlator has 6 independent units, each being tunable anywhere in the 110-610 MHz band, and providing 4 choices of bandwidth/channel configuration: 160 MHz/64, 80 MHz/128, 40 MHz/256 and 20 MHz/256. For the 40, 80 and 160 MHz bandwidth, the two central channels may be perturbed by the Gibbs phenomenon (depending on continuum strength): it is recommended to avoid centering the most important part of the lines in the middle of the band of the correlator unit.

The 6 units can be independently placed either on IF1 (3 mm receiver) or on IF2 (1.3 mm receiver).

40 kHz resolution:

One (and only one) of the 6 units has been retrofitted to offer a higher frequency resolution (40 kHz instead of 80 kHz). This is obtained by operating at half clock-speed and inserting an anti-aliasing filter of effective bandwidth 6 MHz. Because the filter reduces the input power to the sampler, this unit should be placed near the maximum amplitude of the IF bandpass: band edges must be avoided.

Sun Avoidance:

For safety reasons, the sun avoidance circle has been extended to 45 degrees. Please take this into account for your sources and for the calibrators.

Mosaics:

The PdBI has mosaicing capabilities, but the pointing accuracy may be a limiting factor at the highest frequencies. Please contact S.Guilloteau in case of doubts.

Data reduction:

Proposers should be aware of constraints for data reduction:

• In general, data will be reduced in Grenoble. Proposers will not come for the observations, but will have to come for the reduction.
• We keep the data reduction schedule very flexible, but wish to avoid the presence of more than 2 groups at the same time in Grenoble. Please contact us in advance.
• IRAM may consider splitting the data reduction in two phases: intermediate calibration and final mapping. Such a splitting is often absolutely necessary for the high resolution images. In such a case, the proposers must be ready to come at IRAM for fast data reduction of the ``compact'' configurations.
• CLIC is still evolving fast to cope with the evolution of the PdBI array. The newer versions are upward compatible with the previous releases, but the reverse is not true. Observers wanting to finish data reduction at their home institute should obtain an updated version of CLIC, which is now available. Because differences between CLIC versions may potentially result in imaging errors if new data is reduced with an old package, we insist that observers having a copy of CLIC take special care in maintaining it up-to-date.

Data reduction will be carried out on the dedicated HP workstation.

Local contact:

Depending upon the programme complexity, IRAM may require an in-house collaborator instead of the normal local contact.

Technical pre-screening:

All proposals will be reviewed for technical feasibility in parallel to being sent to the members of the programme committee. Please help in this task by submitting technically precise proposals. Scientific justification should be kept within 2 pages. Note that your proposal must be complete and exact: velocities, position and frequency setup must be exactly specified.

Non-standard observations:

Please contact S.Guilloteau in case of doubt about non-standard programme feasibility.

The documentation for the IRAM Plateau de Bure interferometer includes documents of general interest to potential users:

• An Introduction to the IRAM Plateau de Bure Interferometer.
• IRAM Plateau de Bure Interferometer: Calibration CookBook.
• IRAM Plateau de Bure Interferometer: Mapping CookBook.
• IRAM Plateau de Bure Interferometer: Frequency Setup.
• CLIC: Continuum and Line Interferometer Calibration.

• IRAM Plateau de Bure Interferometer: OBS Users Guide.
• IRAM Plateau de Bure Interferometer: Amplitude Calibration.
• IRAM Plateau de Bure Interferometer: Flux Measurements.
• IRAM Plateau de Bure Interferometer: Pointing Parameters.
• IRAM Plateau de Bure Interferometer: Trouble Shooting Guide.

Finally, we would like to stress again the importance of the quality of the observing proposal. The technical preparation of observing proposals is unfortunately often insufficient. In the past, proposals were received which did not even include exact observing frequencies or even source coordinates, or worse, with coordinates with the wrong epoch !... The IRAM interferometer is a powerful, but complex and unique instrument, and proposal preparation requires special care. Information is available in the documentation, and the IRAM staff can help in case of doubts if contacted well before the deadline. Note that the proposal should not only justify the scientific interest, but also demonstrate how the Plateau de Bure interferometer will bring new information.

Stéphane GUILLOTEAU