As every year, we plan to carry out extensive technical work during the summer semester, including the regular maintenance of the antennas. In particular, yet another antenna will be fully equipped with new aluminum panels replacing its current carbon fiber panels. During this period, regular scientific observations will therefore mostly be carried out with the five element array. We plan to start the maintenance at the latest by the end of May and to schedule the D configuration between June and October.
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|
The following configuration sets are available:
Finally, enter ANY in the proposal form if your project doesn't need any particular configuration.
Please consult the documentation An Introduction to the IRAM interferometer (http://www.iram.fr/IRAMFR/PDB/docu.html) for further details.
All antennas are equipped with dual polarization receivers for the 3mm, 2mm, and 1.3mm atmospheric windows. The frequency range is 80GHz to 116GHz for the 3mm band, 129GHz to 174GHz for the 2mm band, and 201 to 267GHz for the 1.3mm band.
|Band 1||Band 2||Band 3|
|/[dB]||-10||-12 ... -10||-12 ... -8|
Each band of the receivers is dual-polarization with the two RF channels of one band observing at the same frequency. The three different bands are not co-aligned in the focal plane (and therefore on the sky). Due to the pointing offsets between the different frequency bands, only one band can be observed at any time. One of the two other bands is in stand-by mode (power on and local oscillator phase-locked) and is available, e.g., for pointing. Time-shared observations between different RF bands are presently being tested. Please contact the Interferometer Science Operations Group (sogiram.fr) to discuss the feasibility in case you are interested to use this mode.
The mixers are single-sideband, backshort-tuned; they will usually be tuned LSB, except for the upper part of the frequency range in all three bands where the mixers will be tuned USB.
The typical image rejection is 10dB. Each IF channel is 4 GHz wide (4-8 GHz). The two 4 GHz wide IF-channels (one per polarization) can be processed only partially by the existing correlator. A dedicated IF processor 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.
The rms noise can be computed from
Investigators have to specify in the ``technical justification'' and on the Technical Sheet the one sigma noise level which is necessary to achieve each individual goal of a proposal, and particularly for projects aiming at deep integrations.
For best position accuracy, source coordinates must be in the J2000.0 system.
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.
At any given time, only one frequency band can be observed, 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 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.
Where is the selected sky frequency in the IF band? It would be natural to tune the receivers such 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). In all three bands, 3mm, 2mm, and 1.3mm 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).
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.
The software ASTRO can be used to simulate the
receiver/correlator configuration. Astronomers are urged to
download the most recent version of GILDAS at http://www.iram.fr/IRAMFR/GILDAS/
to prepare their proposals.
The previous LINE command has been replaced by several new commands (see internal help; the following description applies to the current receiver system). The behavior of the LINE command can be changed by the SET PDBI 1995|2000|2006 command, that selects the PdBI frontend/backend status corresponding to years 1995 (old receivers, 500 MHz bandwidth), 2000 (580 MHz bandwidth), 2006 (new receivers and new IF processor, 1GHz bandwidth). Default is 2006:
! choice of receiver tuning line xyz 93.2 lsb low 6500 ! choice of the correlator windows narrow Q3 Q3 ! correlator unit #1, on entry 1 spectral 1 20 600 /narrow 1 ! correlator unit #2, on entry 1 spectral 2 20 735 /narrow 1 ! correlator unit #3, on entry 1 spectral 4 320 300 /narrow 1 ! correlator unit #4, on entry 2 spectral 4 320 666 /narrow 2 ...
For safety reasons, a sun avoidance limit is enforced at 45 degrees from the sun. We are presently testing a reduced sun avoidance circle at 35 degrees and expect that projects observed in the summer semester may already profit from this reduction. This can however not be guaranteed yet and we therefore ask proposers to still take into account the 45 degrees limit for the target sources.
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 http://www.iram.fr/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.