Call for proposals on the interferometer

Conditions for the next winter session

Proposals are thus invited for the 5 antenna interferometer, with the same set of stations as last year. Moreover, because of the access restrictions, we wish to minimize logistic problems on the Plateau de Bure next winter.

Possible ways to do so which are currently under consideration include:

• A reduced set of configurations (e.g. no C1 or no B2 configuration)
• Minimizing snow cleaning by e.g. dropping the longest baseline (A) configuration, or fixing the configuration schedule well in advance.
• Focusing the efforts on a particular type of projects (e.g. detection demanding D configuration)

We want our decisions to be based on scientific requirements as much as possible. Accordingly, proposers are strongly encouraged to emphasize in their proposals:

• The uniqueness of Plateau de Bure for the scientific goals
• The possible observing tradeoff, in particular for mapping projects
• The relative urgency of the proposition, in particular if it is relevant for a PhD thesis
• The degree of internal priority when several proposals are issued by the same team.

In view of the serious impact that the accident has, IRAM will seek the advice from an exceptional advisory panel before taking a final decision on the overall strategy for the next winter (and summer) period.

We still expect to be able to perform the equivalent of about 30-40 full synthesis during next winter. However, projects will be carried on a ``best effort'' basis.

Call for Proposals on the interferometer

Following the above rules, proposals are invited for the IRAM Plateau de Bure Interferometer (PdBI) for the period Nov. 15th, 1999 to May 15, 2000. The deadline for applications is Sept 10 th, 1999 18:00h (MET). Applications may now be submitted via the World-Wide-Web using the new electronic proposal submission facility, which will be activated three weeks before the deadline.

IRAM expects to schedule and complete at least 30-40 projects with 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.

Details of the PdBI and the observing procedures are given in the document ``The Plateau de Bure Interferometer (PdBI)''. A copy can be obtained from the address below or from Internet via the World-Wide-Web (use IRAM's page at http://iram.fr/PDBI/bure.html). Proposers should read this document carefully before submitting any proposal.

Applications sent by fax or postal mail should be addressed to:

IRAM Scientific Secretariat
Interferometer Observing Proposal
300 Rue de la Piscine
F-38406 Saint Martin d'Hères Cedex
FRANCE

Proposal templates as well as the Latex style file proposal.sty may be obtained by anonymous ftp from iram.fr (directory dist/proposal); or from Internet via the World-Wide-Web at http://iram.fr/proposal/proposal.html. In case of problems, contact the secretary, Cathy Berjaud.

We encourage the use of the electronic submission facility. Proposals sent by e-mail, however, will not be accepted. Do not use characters smaller than 11pt, which could make your proposal illegible when copied or faxed. For the same reasons, also avoid sending by fax figures with grey scale maps. In case your proposal reaches us in time, but is incomplete or unreadable when copied, we will try out best to contact you. The Principal Investigator will receive by return mail an acknowledgement of receipt and the proposal number.

The scientific aims of the proposed programme should be explained in 2 pages of text maximum, plus up to two pages of figures, tables, and references. Proposals should be self-explanatory, clearly state the scientific aims, and explain the need of the Plateau de Bure interferometer.

In all cases, indicate on the first page whether your proposal is (or is not) the resubmission of a previously rejected proposal or the continuation of a previously accepted proposal. In case of a resubmission, state very briefly in the introduction why the proposal is being resubmitted (e.g. improved scientific justification).

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

Backup Projects for the May-Nov. 1999 period

Because of longer than foreseen antenna maintenance, not all the backup projects for the summer period will be scheduled. We urge proposers to re-submit them unless they have explicitly been notified of their effective scheduling.

Proposal category

Proposals should be submitted for one of the five categories:

1.3mm:

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

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.

dual freq.:

Proposals that ask for dual-frequency observations (i.e. simultaneous observations at 3mm and 1.3mm).

time filler:

Proposals that have to be considered as background projects to fill in periods where the atmospheric conditions do not allow mapping, or eventually, to fill in gaps in the scheduling, or even periods when only a subset of the standard 4 and 5-antenna 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; for this winter non-standard configurations will not be considered.

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

Configurations

Standard configurations for the next winter period are:

5 Antenna configurations
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

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

The time order of the configurations for a given project cannot be guaranteed. Enter ANY in the proposal form if your project doesn't need any particular configuration.

Receivers

All antennas are equipped with fully operational dual frequency receivers. The available frequency range will be 82 GHz to 116 GHz for the 3mm band, and 210 to 245 GHz for the 1.3 mm band. The 3mm and 1.3mm receivers are aligned to within about 2''.

Below 110 GHz, receivers offer best performances in LSB tuning with high rejection (20 dB): expected system temperatures are (in $T_{\rm R}^{*}$ 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 $_{\rm REC}$ 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.

1.3mm band observations

Experience based on past years shows that sub-arc-second resolution can be achieved in good winter conditions, 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.

Signal to Noise

The rms noise can be computed from

$$\sigma = \frac{J_{\rm pK}\,T_{\rm SYS}} {\eta \sqrt{N_{\rm a}(N_{\rm a}-1)N_{\rm c} T B}}$$ (1)

where

• $T_{\rm SYS}$ is the system temperature in T_r^* scale (150 K below 110 GHz, 200 K at 115 GHz, 400 K at 230 GHz)
• $J_{\rm pK}$ is the conversion factor from Kelvin to Jansky (22 at 3mm, 40 at 1.3mm)
• $\eta$ is an efficiency factor due to atmospheric phase noise (0.9 at 3 mm, 0.8 at 1.3 mm)
• $N_{\rm a}$ is the number of antennas (5), and $N_{\rm c}$ is the basic number of configurations (1 for D, 2 for CD, 3 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 observations, according to the spectral correlator setup)

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 extends 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 R. Neri in case of doubt.

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 are 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

A local contact will be assigned to every proposal which does not involve an in-house collaborator. 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. Note that your proposal must be complete and exact: velocities, position and frequency setup must be exactly specified.

Non-standard observations

Please contact R.Neri, R.Lucas, or A. Dutrey in case of doubt about non-standard program feasibility. All documents can be retrieved on Internet via the World-Wide-Web. IRAM's home page is http://iram.fr/

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 at http://iram.fr/PDBI/bure.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 demonstrate how the Plateau de Bure interferometer will bring new information.

Roberto NERI