As every year, we plan to carry out extensive technical work during the summer semester, including the regular maintenance of the antennas. During this period, regular scientific observations will therefore mostly be carried out with the five element array. In addition to the antenna maintenance, an upgrade of the computer system on Bure will be carried out. All HPUX and OS9 systems will be replaced by LINUX PCs along with major modifications of the corresponding antenna control and data acquisition software in the real-time system. Further work will be done on the reduction of the sun avoidance circle. Finally, new receivers operating in the 2mm band will be installed on all six antennas. This new set of receivers, which will open a new frequency band at the Plateau de Bure interferometer, will be become available for the community at the end of the summer semester, after thorough testing and commissioning.
We plan to start the maintenance at the latest by the end of May and to schedule the 5D configuration between June and September. Scheduling of the 6D and 6C configurations will be tailored to progress being made in the commissioning of the 2mm NGR system.
We strongly encourage observers to submit proposals that can be executed during summer operating conditions. To keep the procedure as simple as possible, we ask to focus on:
|5Dq||W08 E03 N07 N11 W05|
|6Dq||W08 E03 N07 N11 N02 W05|
|6Cq||W12 E10 N17 N11 E04 W09|
Part of the projects will be scheduled at the end of the summer period
when the six-element array is expected to be back to
operation. Projects that should be observed with a subset of the
five-element array, will be adjusted in uv-coverage and observing
The following configuration sets are available:
|D||Detection + ``low'' resolution mapping at 1.3mm|
|CD||3.5 resolution mapping at 3mm|
Each band of the new receivers is dual-polarization (two RF and IF channels) with the two RF channels of one band observing at the same frequency (common LO). The different bands are not co-aligned in the focal plane (and therefore on the sky). The mixers are single-sideband, backshort-tuned; they can be tuned USB or LSB, both choices being available in the central part of the RF band. The typical image rejection is 10dB. Each IF channel is 4 GHz wide (4-8 GHz). Only one frequency band can be connected to the IF transmission lines at any time. Because of this reason and due to the 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. Time-shared observations between two frequency bands can not be offered for the summer (this mode is currently being tested).
The two IF-channels (one per polarization), each 4 GHz wide (total 8 GHz) 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 1 GHz wide slices of the 4-8 GHz first IFs down to 0.1-1.1 GHz, 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 3|
|RF range in LSB||81-104||201-244|
|RF range in 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 4 GHz bandwidth (from IF=4 to 8 GHz). The two 4-GHz bandwidths coincide in the sky frequency scale. The current correlator accepts as input two signals of 1 GHz bandwidth, that must be selected within the 4 GHz delivered by the receiver. In practice, the new IF processor splits the two input 4-8 GHz bands in four 1 GHz ``quarters'', labeled Q1...Q4. Two of these quarters must be selected as correlator inputs. The system allows the following choices:
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 give access
to 1 GHz 2 polarizations.
How to use the full 2 GHz bandwidth? If two different quarters
are selected (any combination is possible), a bandwidth of 2 GHz 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 1 GHz.
Is there any overlap between the four quarters? In fact, the
four available quarters are 1 GHz wide each, but with a small overlap
between some of them: Q1 is 4.2 to 5.2 GHz, Q2 is 5 to 6 GHz, Q3 is
6 to 7 GHz, and Q4 is 6.8 to 7.8 GHz. This results from the combination
of filters and LOs used in the IF processor.
Is the 2 GHz bandwidth necessarily continuous? No: any combination
of two quarters can be selected. Adjacent quarters will result in a
continuous 2 GHz band. Non-adjacent quarters will result in two
independent 1 GHz 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. 6.0 GHz. 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 Q2
(i.e. the line should be centered at an IF1 frequency of 5500 MHz)
whereas at 1mm best performance is obtained in Q3 (i.e. the line
should be centered at 6500MHz).
The correlator has 8 independent units, which can be placed anywhere in the 100-1100 MHz band (1 GHz 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.
Note that 5% of the passband is lost at the end of each
subband. The 8 units can be independently connected to the first or
the second correlator entry, as selected by the IF processor (see
above). Please note that the center frequency is expressed - as in the
old system - in the frequency range seen by the correlator, i.e. 100
to 1100 MHz. The correspondence to the sky frequency depends on
the parts of the 4 GHz bandwidth which have been selected as correlator
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.