Based on our experience in carrying out configuration changes in winter conditions with limited access to the observatory, we plan to schedule four configuration changes next winter. We therefore ask investigators to submit proposals for any of the 4 primary configurations of the six antenna array.
A preliminary configuration schedule for the winter period is outlined below. Adjustments to the provisional configuration planning will be made according to proposal pressure, weather conditions, installation of the 2mm receiver band and other contingencies. Due to the installation of the new generation receivers last fall, the C configuration was not available in December, and this spring not all of the projects requesting the C configuration could be worked off. These projects are now postponed for the C configuration to be scheduled at the end of the summer semester and at the beginning of the upcoming winter. We therefore may again have less time available in C configuration this winter than in regular previous years. The configuration schedule given below should be taken as a guideline, in particular when the requested astronomical targets cannot be observed during the entire winter period (sun avoidance circle of radius 45).
|Conf||Scheduling Priority Winter 2007/2008|
|A||December - January|
|B||February - March|
|C||March - April|
|D||April - May|
We strongly encourage observers to submit proposals for the new set of AB configurations that include 730 and 760 meter baselines. For these proposals we ask to focus on bright compact sources, possibly at high declination.
We invite proposers to submit proposals also for observations at 3mm. When the atmospheric conditions are not good enough at 1.3mm, 3mm projects will be observed: in a typical winter, % of the time used for observations is found to be poor at 1.3mm, but still excellent at 3mm.
Proposals requesting the 2mm band should be submitted on a shared-risk basis only.
All applications under this call for proposals will have to take into account that the new receivers cannot be operated simultaneously at more than one frequency band. Investigators will therefore have to make it clear whether a request is made for one (e.g., 3mm) or more (e.g., 3mm and 1mm) frequency bands.
Proposals should be submitted for one of the five following categories:
The proposal category will have to be specified on the proposal cover sheet and should be carefully considered by proposers.
The six-element array can be arranged in the following
The general properties of these configurations are:
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.
Please consult the documentation on the Plateau de Bure configurations and the IRAM Newsletter No. 63 (August 4th., 2005, accessible on the web at ../IRAMFR/ARN/aug05/aug05.html) for further details.
Since December 2006, all antennas are equipped with a new generation of dual polarization receivers for the 3mm and 1.3mm atmospheric windows. The frequency range is 81GHz to 116GHz for the 3mm band, and 201GHz to 256GHz for the 1.3mm band. For the upcoming winter semester, the 2mm band may additionally become available, covering the frequency range 129GHz to 168GHz.
Each band of the new receivers is dual-polarization with the two RF channels observing at the same frequency. The mixers are single-sideband, with a typical image rejection of 10dB. Only one frequency band (dual polarization) can be connected to the IF transmission lines at any time. Because of this reason and due to pointing offsets between different frequency bands, only one band can be observed at any time. The other band is in stand-by (power on and local oscillator phase-locked) and is available, e.g., for pointing and focusing. Time-shared observations between two frequency bands cannot be offered for the winter (this mode is currently being tested).
The two IF-channels (one per polarization), each 4GHz wide, are transmitted by optical fibers to the central building. At present, the 4GHz bandwidth can be processed only partially by the existing correlator, through a dedicated IF processor that converts selected 1GHz wide slices of the 4-8GHz first IFs down to 0.1-1.1GHz, the input range of the existing correlator. Further details are given in the section describing the correlator setup and the IF processor.
|PdBI Receiver Specifications|
|Band 1||Band 2||Band 3|
|RF range LSB||81-104||201-244|
|RF range USB||104-116||244-256|
The rms noise can be computed from
Investigators have to specify the one sigma noise level which is necessary to achieve each individual goal of a proposal, and particularly for projects aiming at deep integrations.
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.
At any given time, only one frequency band is used, but with the two polarizations available. Each polarization delivers a 4GHz bandwidth (from IF to 8GHz). The current correlator accepts as input two signals of 1GHz bandwidth, that must be selected within the 4GHz delivered by the receiver. In practice, the new IF processor splits the two input 4-8GHz bands in four 1GHz ``quarters'', labeled Q1...Q4. The system allows the following choices:
where HOR and VER refers to the two polarizations:
|IF1 [GHz]||4.2 - 5.2||5 - 6||6 - 7||6.8 - 7.8|
How to observe two polarizations? To observe simultaneously two polarizations at the same sky frequency, one must select the same quarter (Q1 or Q2 or Q3 or Q4) for the two correlator entries. This will necessarily result in each entry seeing a different polarization. The system thus gives access to 1GHz x 2 polarizations.
How to use the full 2GHz bandwidth? If two different quarters are selected (any combination is possible), a bandwidth of 2GHz can be analyzed by the correlator. But only one polarization per quarter is available in that case; this may or may not be the same polarization for the two chunks of 1GHz.
Is there any overlap between the four quarters? In fact, the four available quarters are 1GHz wide each, but with a small overlap between some of them: Q1 is 4.2 to 5.2GHz, Q2 is 5 to 6GHz, Q3 is 6 to 7GHz, and Q4 is 6.8 to 7.8GHz. This results from the combination of filters and LOs used in the IF processor.
Is the 2GHz bandwidth necessarily contiguous? No: any combination of two quarters can be selected. Adjacent quarters will result in a continuous 2GHz band. Non-adjacent quarters will result in two independent 1GHz bands. Note that in any case, the two correlator inputs are analyzed independently.
Where is the selected sky frequency in the IF band? It would be natural to tune the receivers so that the selected sky frequency corresponds to the middle of the IF bandwidth, i.e. 6.0GHz. However, this corresponds to the limit between Q2 and Q3. It is therefore highly recommended to center a line at the center of a quarter (see Section ``ASTRO'' below). At 3mm, the receivers offer best performance in terms of receiver noise and sideband rejection in Q3 (i.e. the line should be centered at an IF1 frequency of 6500 MHz) whereas at 1mm best performance is obtained in Q2 (i.e. the line should be centered at 5500MHz).
The correlator has 8 independent units, which can be placed anywhere in the 100-1100MHz band (1GHz bandwidth). 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.
|0.039||1 x 512||20||SSB|
|0.078||1 x 512||40||SSB|
|0.156||2 x 256||80||DSB|
|0.312||1 x 256||80||SSB|
|0.625||2 x 128||160||DSB|
|1.250||1 x 128||160||SSB|
|2.500||2 x 64||320||DSB|
The software ASTRO has been updated to reflect these new
receiver/correlator setup possibilities. Astronomers are urged to
download the most recent version (February 2007 or later) of GILDAS
at ../IRAMFR/GILDAS/ to prepare their proposals.
The old LINE command has been replaced by several new commands (see internal help):
! choice of receiver tuning ngr_line xyz 230 lsb ! choice of the correlator windows narrow Q1 Q3 ! correlator unit #1, on entry 1 spectral 1 20 520 /narrow 1 ! correlator unit #2, on entry 1 spectral 2 320 260 /narrow 1 ! correlator unit #3, on entry 2 spectral 3 40 666 /narrow 2 ...
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 this
call 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.