Call for Observing Proposals for the Plateau de Bure Interferometer

Conditions for the next winter session

Based on our experience in carrying out configuration changes with limited access to the Observatory, we plan to schedule three configuration changes next winter. We therefore ask investigators to submit proposals for all 4 of the current primary configurations of the six antenna array. Projects will be properly adjusted in observing time and uv-coverage, in collaboration with the principal investigators, should the new configurations (see preceding section ``News from the Plateau de Bure Interferometer'') become available in time for the winter scheduling period.

A preliminary configuration schedule for the winter period is outlined below. Please note that the more compact configurations (C and D) will be available only at the end of January at the earliest. The scheduling priority will later be adapted according to pressure in right ascension ranges and may further be changed during the winter period depending on weather conditions. The configuration schedule should be taken as a guideline, in particular when the requested astronomical targets cannot be observed during the entire winter period (45$^\circ$ sun avoidance circle).

Conf	Scheduling Priority Winter 2005/2006
B	November - December
A	December - January
C	February - March
D	March - April

We strongly encourage observers to submit proposals that would highly benefit from observations in the new set of AB configurations. For these proposals we ask to focus on:

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bright compact sources, possibly at high declination,

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observations that qualify also for the 3mm receivers.

When the atmospheric conditions are not good enough at 1.3mm, 3mm projects will be observed: in a typical winter, 20-30% of the observing time is found to be poor at 1.3mm, but still excellent at 3mm. We therefore invite proposers to submit proposals also for observations at 3mm.

Call for Proposals

Under normal operating conditions, IRAM schedules and completes between 40 to 60 projects during the winter period, with an elapsed time of at least two months between start and end of a project, on average. Selection is based on scientific merit, technical feasibility, and suitability for the instrument.

Details of the PdBI and the observing procedures are given in the document ``An Introduction to the IRAM Plateau de Bure Interferometer''. A copy can be obtained from the address below or from the World-Wide-Web at ./IRAMFR/PDB/docu.html. Proposers should read this document carefully before submitting any proposal.

Proposal category

Proposals should be submitted for one of the five categories:

dual freq.:

Proposals that ask for simultaneous observations at 3mm and 1.3mm.

1.3mm:

Proposals that ask for 1.3mm data only. 3mm receivers will be used for pointing and calibration purposes, but the scientific goals of the proposal rely on the 1.3mm receivers.

3mm:

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.

time filler:

Proposals that have to be considered as backup projects to fill in periods where the atmospheric conditions do not allow mapping, or eventually, to fill in gaps in the scheduling, or periods when only a subset of the standard configurations will be available. These proposals will be carried out on a ``best effort'' basis only.

special:

Exploratory proposals: proposals whose scientific interest justifies the attempt to use the PdB array beyond its guaranteed capabilities. This category includes, for example, non-standard frequencies for which the tuning cannot be guaranteed, and more generally all non-standard observations. These proposals will be carried out on a ``best effort'' basis only.

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

Configurations of the six-antenna array

The six-element array can presently be arranged in the following configurations:

Conf	Stations
A	W27	W23	E16	E23	N13	N29
B	W12	E04	E23	N07	N17	N29
C	W12	E10	E16	N02	N09	N20
D	W05	W00	E03	N05	N09	N13

Note that a new set of configurations is proposed for the upcoming winter semester (see preceding contribution ``News from the Plateau de Bure Interferometer''), should work on the eastern and northern track extension be completed in time.

The general properties of the current configurations (see also Table 2, section ``News from the Plateau de Bure Interferometer'') are:

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A alone is well suited for mapping or size measurements of very compact objects. It provides a resolution of $1.1''$ at 100GHz, $\sim$0.5$''$ at 230GHz. In addition, because it contains long, intermediate and some short baselines, it could still be used in a tapered mode when a project is observed in marginal weather conditions despite some loss of sensitivity (for backup projects).

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B in combination with A already provides slightly higher angular resolution ($\sim$1.5$''$ at 100GHz). Short baselines have been included to facilitate calibration (less decorrelation) and give some sensitivity to extended structure, although this is clearly not the primary goal of the AB configuration. It is mainly used for relatively strong sources.

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C provides a fairly complete coverage of the uv-plane (low sidelobe level) and is well adapted to combine with D for low angular resolution studies ($\sim$3.5$''$ at 100GHz, $\sim$1.5$''$ at 230GHz) and with B for higher resolution ($\sim$2$''$ at 100GHz, $\sim$0.9$''$ at 230GHz). C alone is also well suited for snapshot and size measurement experiments.

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D alone is best suited for deep integration and coarse mapping experiments. This configuration provides both the highest sensitivity and the lowest atmospheric phase noise. It is slightly more extended than the 5-element D configuration: the beam is smaller, but slightly more elliptical.

The four configurations can be used in different combinations to achieve complementary sampling of the uv-plane, and to improve on angular resolution and sensitivity. Mosaicing is usually done with D or CD, but the combination BCD can also be requested for high resolution mosaics. Check the ANY bullet in the proposal form if the scientific goals can be reached with any of the four configurations or their subsets.

Investigators interested in observations with the new set of extended configurations only, should check the NEW bullet in addition to the requested configurations. Note that the general properties of the current configurations also apply to the new configurations.

Please consult the documentation on the Plateau de Bure configurations for further details.

Receivers

All antennas are equipped with fully operational dual frequency receivers. The guaranteed frequency range will be 82 to 116 GHz for the 3mm band, and 205 to 245 GHz for the 1.3 mm band. The 3mm and 1.3mm receivers are aligned to within about $2''$.

Below 105 GHz, receivers offer best performances in LSB tuning with high rejection (20 dB): expected system temperatures are 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.

The 1.3 mm receivers have DSB tuning with typical T$_{\rm REC}$ below 50 K. Expected SSB system temperature are 350 to 450 K. The guaranteed tuning range is 205-245 GHz, but it is possible to reach some lower and higher frequencies. Higher frequencies are not feasible on all antennas because of limitations in the triplers. For details about observing at frequencies slightly below or above the guaranteed tuning range of the 3mm and 1.3mm receivers, please get in touch with the Interferometer Science Operations Group (sog$@$iram.fr).

Signal to Noise

The rms noise can be computed from

$$\sigma = \frac{\JpK\mbox{$T_{\rm SYS}$}} {\eta \sqrt{\Na (\Na -1) \Nc T_{\rm ON} B}}$$ (1)

where

• $\hbox{$J_{\rm pK}$}$ is the conversion factor from Kelvin to Jansky (22 Jy/K at 3mm, 35 Jy/K at 1.3mm)
• $T_{\rm SYS}$ is the system temperature (150 K below 110 GHz, 200 K at 115 GHz, 400 K at 230 GHz for sources at $\ge 20^\circ$)
• $\eta$ is an efficiency factor due to atmospheric phase noise (0.9 at 3 mm, 0.8 at 1.3 mm).
• $\hbox{$N_{\rm a}$}$ is the number of antennas (6), and $\hbox{$N_{\rm c}$}$ is the number of configurations: 1 for D, 2 for CD, 2 for BC, and so on.
• $T_{\rm ON}$ is the on-source integration time per configuration in seconds (2 to 8 hours, depending on source declination). Because of various calibration observations the total observing time is typically 1.4 $T_{\rm ON}$.
• $B$ is the spectral bandwidth in Hz (580 MHz for continuum, 40 kHz to 2.5 MHz for spectral line, according to the spectral correlator setup)

Investigators have to specify the $1\sigma$ noise level which is necessary to achieve each individual goal of a proposal, particularly for projects aiming at deep integrations.

Coordinates and Velocities

The interferometer operates in the J2000.0 coordinate 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 new correlator has 8 independent units, which can be placed anywhere in the 100-680 MHz band. 7 different modes of configuration are available, characterized in the following by couples of total bandwidth/number of channels. In the 3 DSB modes (320MHz/128, 160MHz/256, 80MHz/512 - see Table) the two central channels may be perturbed by the Gibbs phenomenon if the observed source has a strong continuum. When using these modes, it is recommended to avoid centering the most important part of the lines in the middle of the band of the correlator unit. In the remaining SSB modes 160MHz/128, 80MHz/256, 40MHz/512, 20MHz/512) the two central channels are not affected by the Gibbs phenomenon and, therefore, these modes may be preferable for some spectroscopic studies.

Spacing	Channels	Bandwidth	Mode
(MHz)		(MHz)
0.039	$1 \times 512$	20	SSB
0.078	$1 \times 512$	40	SSB
0.156	$2 \times 256$	80	DSB
0.312	$1 \times 256$	80	SSB
0.625	$2 \times 128$	160	DSB
1.250	$1 \times 128$	160	SSB
2.500	$2 \times 64$	320	DSB

Note that 5% of the passband is lost at each end of a subband. The 8 units can be independently connected either with the 3mm or 1.3mm IFs.

Sun Avoidance

For safety reasons, a sun avoidance circle is enforced at 45 degrees. Please take this into account for your sources AND calibrators.

Mosaics

The PdBI has mosaicing capabilities, but the pointing accuracy may be a limiting factor at the highest frequencies. Please contact the Interferometer Science Operations Group (sog$@$iram.fr) 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 may have to come for the data 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.
• In certain cases, proposers may have a look at the uv-tables as the observations progress. If necessary, and upon request, more information can be provided. Please contact us if you are interested in this possibility.
• CLIC evolves to cope with upgrades of the PdBI array. The newer versions are downward compatible with the previous releases. Observers who wish to finish data reduction at their home institute should obtain the most recent version of CLIC. Because differences between CLIC versions may potentially result in imaging errors if new data are reduced with an old package, we advise observers having a copy of CLIC to take special care in maintaining it up-to-date.

Data reduction will be carried out on dedicated computers at IRAM. Remote data reduction is possible, and especially for experienced users of the Plateau de Bure Interferometer. Please contact the Interferometer Science Operations Group (sog$@$iram.fr) if you're interested in this possibility.

Local contact

A local contact will be assigned to every A or B rated proposal which does not involve an in-house collaborator. He/she will assist you in the preparation of the observing procedures and provide help to reduce the data. Assistance is also provided before a deadline to help newcomers in the preparation of a proposal. 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 addition to the scientific review by the programme committee. Please help in this task by submitting technically precise proposals. Note that your proposal must be complete and exact: the source position and velocity as well as the requested frequency setup must be correctly given.

Non-standard observations

If you plan to execute a non-standard program, please contact the Inteferometer Science Operations Group (sog$@$iram.fr) to discuss the feasibility.

Documentation

The documentation for the IRAM Plateau de Bure Interferometer includes documents of general interest to potential users, and more specialized documents intended for observers on the site (IRAM on-duty astronomers, operators, or observers with non-standard programs). All documents can be retrieved on the Internet at ./IRAMFR/PDB/docu.html

Finally, we would like to stress again the importance of the quality of the observing proposal. The IRAM interferometer is a powerful, but complex instrument, and proposal preparation requires special care. Information is available in the documentation and at ./IRAMFR/PDB/docu.html. 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 the need for the Plateau de Bure Interferometer.

Roberto NERI