Call for Observing Proposals on the Plateau de Bure Interferometer

Observing proposals are invited for the IRAM Plateau de Bure Interferometer (PdBI), for the period Nov. 15, 1997 to May 15, 1998. The deadline for applications is September 8th, 1997. The available frequency range will be 82 GHz to 116 GHz for the 3mm band, and 210-245 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; use IRAM's home page http://iram.fr/). 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 30 to 50 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:

Proposal Category:

 
Proposals should be submitted for one of the 4 categories defined below:

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.

Category 2:

Proposals that ask for 1.3mm data ONLY. 3mm receivers will be used for pointing and calibration purposes, but cannot provide any imaging.

Category 3:

Proposals that ask for dual-frequency observations.

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 observing at non-standard frequencies for which tuning cannot be guaranteed, and more generally all non-standard observations. These proposals will be carried out on a ``best effort'' basis.

The proposal category will have to be specified on the proposal cover sheet, and should be carefully considered by proposers.

Backup Projects for the May-Nov. 1997 period

 
Because of heavy antenna maintenance, backup projects for the last period have not all been scheduled. We urge proposers to re-submit them unless they have explicitly been notified of their effective scheduling.

Configurations

 
The available configurations include:

Name Stations

D W05 W00 E03 N05 N09

C1 W05 W01 E10 N07 N13

C2 W12 W09 E10 N05 N15

B1 W12 E18 E23 N13 N20

B2 W23 W12 E12 N17 N29

A W27 W23 E16 E24 N29

With 5 antennas, the following configuration sets are available:

Set Configs Main purpose

D D ``Low'' resolution at 1.3 mm

CD D, C2 or C1 3.5'' resolution at 3mm, 1.8'' resolution at 1.3 mm

CC C1, C2 Slightly higher resolution than CD.

BC B1, C2 2'' resolution at 3 mm

BB B1, B2, C2 Better sensitivity than BC

AB A, B1, B2 1'' resolution at 3 mm, 0.5'' resolution at 1.3mm

There is a possibility of choice between CD and CC arrays when the C2 configuration has been performed for sources in which the resolution choice is unclear. At a higher resolution level, a similar choice between CC and BC or BB is possible.

1.3 mm band

 
All antennas are now equipped with fully operational dual frequency receivers. Experience of the last winter shows that 1.8'' can be easily reached (CD array). Sub-arc-second resolution has been obtained on a few projects, but cannot be guaranteed.

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

Atmospheric Phase Compensation

 
Software is available to provide real-time atmospheric phase compensation on spectral and continuum data, as well as a-posteriori processing for continuum data. Experience shows that a final phase noise below 30 degrees at 230 GHz is obtained under good circumstances.

Dual-frequency operation

 
The 3mm and 1.3mm receivers are aligned to within about 2''.

Signal to Noise

 
The rms noise can be computed from

where

• is the system temperature in scale (150 K below 110 GHz, 300 K at 115 GHz, 500 K at 230 GHz)
• is the conversion factor from Kelvin to Jansky (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 number of antennas (5), and is the basic number of configurations (with 5 antennas 1 for D, 2 for CD, 3 for BC)
  item 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 performance 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 performance is 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 250 to 350 K. The guaranteed tuning range is 210-245 GHz, but it may be possible to reach lower frequencies for specific cases. Higher frequencies are not feasible 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 8 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 should 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 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 workstations.

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 program 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.

More specialized documents are also available; they are intended for observers on the site (IRAM on-duty astronomers, operators, or observers with non-standard programmes):

• 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