
\section{News from the Plateau de Bure Interferometer}

Following the successful installation and commissioning of the Next
Generation Receivers (NGRs) for the 3\,mm and 1.3\,mm atmospheric
windows last fall, regular observing was resumed on January 18th, 2007 
when
the array was in its 6D configuration. We switched to the A
configuration (that provides baselines up to 760m) was achieved on
January 28 and the baselines were determined with high precision
(better than 14\,deg phase rms at 86\,GHz on  the longest baselines).
It is planned to move to the B configuration around end of February
and to the C configuration by end of March. The switch back to the
most compact configuration D is foreseen before end of
April. According to these plans, it will not be possible to complete
projects requesting deep integrations using the compact configurations 
before the end of the current observing period.

The observing conditions in January were quite mediocre due to the
unusually warm winter in Europe, but they improved considerably by the end
of the month. Only commissioning projects were observed with the NGR
system in D configuration but as of February 13 already 17 tracks have
been scheduled in A configuration for regular user projects.

As far as A-rated projects are concerned, we look forward to bring
many of these to completion before the end of the current winter
semester. B-rated projects are likely to be observed only if they fall
in a favorable LST range. We remind users of the Plateau de Bure
interferometer that B-rated proposals which are not started before the
end of the winter period have to be resubmitted.

Global VLBI observations, which include the array in the 3mm
phased-array mode, are planned from May 10 to 15, 2007.

Investigators, who wish to check the status of their project, may
consult the interferometer schedule on the Web at
../PDBI/ongoing.html. The page is updated daily.

\signed {Jan Martin WINTERS}

\section{Call for Observing Proposals on the Plateau de Bure Interferometer}
\subsection{Conditions for the next summer period} 
\noindent

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 2\,mm 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 2\,mm 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:

\begin{itemize}
\item[$\circ$] observations requesting the use of the 3mm receivers
\item[$\circ$] circumpolar sources or sources transiting at night between 
June and September,
\item[$\circ$] observations that qualify for the 5D, 6D, and 6C configurations
\end{itemize}

\subsection{Proposal category}
Proposals should be submitted for one of the four categories:
\begin{description}
\item[{\sc 1.3mm:}\/] Proposals that ask for 1.3mm data.
3mm receivers can be used for pointing and calibration purposes, but cannot
provide any imaging. 
%\item[{\sc 2mm:}\/] Proposals that ask for 2mm data. These proposals
%will be observed on a shared risk basis as ``science verification''
%projects to inaugurate the new receiver band expected to be available
%after September.
\item[{\sc 3mm:}\/] Proposals that ask for 3mm data.
\item[{\sc 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
5-antenna configurations will be available. These proposals will be
carried out on a ``best effort'' basis only.
\item[{\sc 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,
non-standard configurations and more generally all non-standard
observations. These proposals will be carried out on a ``best effort''
basis only.
\end{description}
The proposal category will have to be specified on the proposal cover
sheet and should be carefully considered by proposers.

\subsection{Configurations}
Configurations planned for the summer period are:
\begin{center}
\begin{tabular}{|l|c|}
\hline
Name & Stations  \\
\hline
5Dq & W08 E03 N07 N11 W05  \\
6Dq & W08 E03 N07 N11 N02 W05  \\
6Cq & W12 E10 N17 N11 E04 W09  \\
\hline
\end{tabular}
\end{center}

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
time.\\

The following configuration sets are available:
\begin{center}
\begin{tabular}{|c|p{4.3cm}|}
\hline
Set & Main purpose \\
\hline
D  & Detection + ``low'' resolution mapping at 1.3mm \\
CD &  3.5$''$ resolution mapping at 3mm \\
\hline
\end{tabular}
\end{center}
Finally, enter {\sc any}\/ in the proposal form if your project
doesn't need any particular configuration. 

\subsection{Receivers}
Since December 2006 all antennas are equipped with a new generation of 
dual polarization receivers for the 3\,mm and 1.3\,mm atmospheric windows. 
The frequency range is 81\,GHz to 116\,GHz for
the 3\,mm band, and 201 to 256\,GHz for the 1.3\,mm band.  

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 10\,dB. 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 4\,GHz 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.

\vskip 4mm \begin{center}
\begin{tabular}{lll}
\hline
\hline
\multicolumn{3}{c}{PdBI Receiver Specifications} \\
       & Band 1  & Band 3 \\
\hline
 RF coverage     &  81--116     &  201--256 \\
 $\rm T_{rec}$   &  40--55      & 40--60 (LSB) \\
 $\rm T_{rec}$   &              & 50--70 (USB) \\
 $\rm G_{im}$    & $\rm -10$~dB & $\rm -12 -8$~dB \\
 RF range in LSB & 81--104      & 201--244 \\
 RF range in USB & 104--116     & 244--256 \\
\hline
\end{tabular}
\end{center}

\subsection{Signal to Noise}

The rms noise can be computed from
\begin{equation}
 \sigma = \frac{J_{\rm pK} T_{\rm sys}} {\eta \sqrt{N_{\rm a} (N_{\rm a}-1) 
N_{\rm c} T_{\rm ON} B}} \frac{1}{\sqrt{N_{\rm pol}}}
\end{equation}
where
\begin{itemize}
\item $J_{\rm pK}$\ is the conversion factor from Kelvin to Jansky (22
Jy/K at 3\,mm, 35 Jy/K at 1.3\,mm)
\item $T_{\rm sys}$ is the system temperature ($T_{\rm sys}$ = 100\,K
below 110\,GHz,  180\,K at 115\,GHz, 250\,K at 230\,GHz for sources at
$\delta \ge 20^\circ$ and for typical summer conditions.)
\item $\eta$ is an efficiency factor due to atmospheric phase noise
(0.9 at 3\,mm, 0.8 at 1.3\,mm).
\item $N_{\rm a}$ is the number of antennas (5), and $N_{\rm c}$ 
is the number of
configurations: 1 for D, 2 for CD, and so on.
\item $T_{\rm ON}$ 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 $T_{\rm ON}$.
\item $B$ is the spectral bandwidth in Hz (up to 2~GHz for continuum, 
40 kHz to 2.5 MHz for spectral line, according to the spectral correlator
setup)
\item $N_{\rm pol}$ is the number of polarizations: 1 for single polarization 
and 2 for dual polarization (see section {\it Correlator} for details).
\end{itemize}

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.

\subsection{Coordinates and Velocities}
The interferometer operates in the J2000.0 system. For best
position accuracy, source coordinates must be in the J2000.0
system; position offsets 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 {\tt 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.

\subsection{Correlator}

\subsubsection{IF processor} 

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 {\em Q1...Q4}. Two of these quarters must be
selected as correlator inputs. The system allows the following
choices:
\begin{itemize}
\item first correlator entry can only be Q1 HOR, or Q2 HOR, or Q3 VER, or Q4 VER
\item second correlator entry can only be Q1 VER, or Q2 VER, or Q3 HOR, or Q4 HOR
\end{itemize}
where HOR and VER refers to the two polarizations:
\begin{flushleft}
\begin{center}
\begin{tabular}{l|cccc}
\hline\noalign{\smallskip}
Quarter  & Q1 & Q2 & Q3 & Q4 \\
IF1 [GHz]& $4.2 - 5.2$ & $5 - 6$ & $6-7$ & $6.8 - 7.8$\\
\noalign{\smallskip}\hline\noalign{\smallskip}
input 1 & H  & H  & V  & V  \\
input 2 & V  & V  & H  & H  
\noalign{\smallskip}\hline
\end{tabular}
\end{center}
\end{flushleft}
\bigskip

{\em 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 $\times$ 2 polarizations. \\

{\em 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. \\

{\em 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. \\

{\em 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. \\

{\em 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 3\,mm, 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 1\,mm best performance is obtained in Q3 (i.e. the line
should be centered at 6500\,MHz).\\

\subsubsection{Spectral units of the correlator} 

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.

\vskip 4mm \begin{center}
\begin{tabular}{crrc}
\hline
\hline
 Spacing & Channels & Bandwidth  & Mode \\
 \multicolumn{1}{c}{(MHz)} & & \multicolumn{1}{c}{(MHz)} & \\
\hline
 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 \\
\hline
\end{tabular}
\end{center}
\vskip 3mm
\noindent 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 
inputs. \\

\subsubsection{ASTRO}

The software {\tt ASTRO} has been updated to reflect these new
receiver/correlator setup possibilities. Astronomers are urged to
download the most recent version ({\bf February 2007 or later}) of GILDAS 
at {\tt ../IRAMFR/GILDAS/ } to prepare their proposals.\\

The old {\tt LINE} command has been replaced by several new
commands (see internal help):
\begin{itemize}
\item {\tt NGR\_LINE}: receiver tuning
\item {\tt NARROW}: selection of the narrow-band correlator inputs
\item {\tt SPECTRAL}: spectral correlator unit tuning
\item {\tt PLOT}: control of the plot parameters. 
\end{itemize}
A typical session would be:

\begin{verbatim}
   ! 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   
   ...
\end{verbatim}


\vskip 4mm
\subsection{Sun Avoidance}
For safety reasons, the sun avoidance circle has been extended to 45
degrees. Please take this into account for your target sources {\sc
and} for the calibrators.

\subsection{Mosaics}
The PdBI has mosaicing capabilities, but the pointing accuracy may be
a limiting factor at the highest frequencies. Please contact the
Science Operations Group (sog@iram.fr) in case of doubts.

\subsection{Data reduction}
Proposers should be aware of constraints for data reduction:
\begin{itemize}
\item[$\circ$] In view of the new receiver system, {\bf data have to
be reduced  in Grenoble}. Proposers will not come for the
observations, but will have to come for the reduction.  For the time
being, remote data reduction will not be offered for projects
observed with the NGR system.
%Remote data reduction is possible, especially for experienced
%users of the Plateau de Bure Interferometer. Please contact your local
%contact if you're interested in this possibility.
\item[$\circ$] 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. Data reduction will be carried out on dedicated computers at
IRAM. Please contact us in advance.
\item[$\circ$] 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 your local contact 
or the Science
Operations Group (sog@iram.fr) if you are interested in this.
\item[$\circ$] 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 NGR 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.  The upgrade of CLIC to handle the NGR data implied many
modifications for which backward compatibility with old PdBI receiver data has
not yet been fully checked. To calibrate data obtained with the ``old''
receiver system, we thus urge you to use the January 2007 version of
CLIC.
\end{itemize}

\subsection{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
program complexity, IRAM may require an in-house collaborator
instead of the normal local contact.

\subsection{Technical pre-screening}
All proposals will be reviewed for technical feasibility in parallel
to being sent to the members of the program 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.

\subsection{Non-standard observations}
If you plan to execute a non-standard program, please contact the
Interferometer Science Operations Group (sog@iram.fr) to discuss the
feasibility.

\subsection{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 {\tt
../IRAMFR/PDB/docu.html}\\
{\bf Note however, that the documentation on 
the web has not yet been updated with respect to the new generation 
receivers. All information currently available on the new generation receiver 
system is given in this call for proposals.}\\ [5mm]

\renewcommand{\finally}{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 {\tt ../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.}

\begin{latexonly}
\fullbox{3mm}{\finally}
\end{latexonly}
\begin{htmlonly}
{\bf \finally}
\end{htmlonly}

\signed {Jan Martin WINTERS}


