Up: IRAM Newsletter 67 (August 2006)
Previous: Proposals for IRAM Telescopes
Proposals for three types of receivers will be considered for the
coming winter semester:
In total, about 2800 hours of observing time will be available,
which should allow
scheduling of a few longer programmes (up to hours).
The main news, proposal formalities, details of the various receivers,
and observing modes are described below.
The telecope is now being operated under a new control system (NCS).
Although allmost all features available under the old
control system are already operational in the NCS, a small number of
restrictions still hold. Most visibly, the only coordinate system fully
supported by the NCS now
is equatorial J2000.0, and we request observers to use this system
for their source coordinates and offsets. Source offsets can be in
the Equatorial J2000.0 system, projection ``radio''; in the ``true
angle'' horizontal system; and in the Nasmyth system (receiver
offsets). SET ANGLE UNIT other than [arcsec] is no yet supported.
The ``Raster'' command is still not available. OTF, ONOFF or TRACKING
(with frequency switching) commands together with SIC loops should be
used instead. Observations with the rotated wobbler which are of
interest for bolometer mapping, are in preparation.
Remote observing is not yet implemented, so astronomers are asked
to travel to the observatory, or in case of short and straightforward
observations, consider service observing.
The NCS team makes a strong effort to maintain a web page
where the current status is described.
The dual polarization HERA is operational together with its
backends for high (VESPA) and low spectral resolution (WILMA, 4 MHz
filters). Although tuning parameters are now available for a large
range of frequencies, it is still recommended to send us HERA
frequencies in advance. HERA observations will be
organized as an observing pool similar to the bolometer observations.
Like last semester, a bolometer array, preferentially the
117-channel MAMBO II, which should be used for observing time
estimates, will be available.
On the official cover page, please fill in the line `special
requirements' if you request either polarimetric observations
or service observing. If the observations need or have to avoid
specific dates, enter them here. If there are periods when you
cannot observe for personal reasons, please specify them here.
We insist upon receiving, with proposals for heterodyne receivers,
a complete list of frequencies corrected for source redshift (to 0.1 GHz)
and precise positions. If in very special cases the proposers do not feel
to be in a position to give this information,
they should take up contact
with the scheduler (thumiram.fr).
The proposers should also specify on the cover sheet which receivers they
plan to use.
In order to avoid useless duplication of observations and to protect already
accepted proposals, we keep up a computerized list of targets.
We ask you to fill out carefully the source list in equatorial
This list must contain all the sources (and only those
sources) for which
you request observing time. To allow electronic scanning of your
source parameters, your list must adhere to the format indicated on the
proposal form (no hand writing, please).
If your source list is longer (e.g. more than 15 sources) than what
fits onto the cover page, please use the LATEX
- the observatory's set of four dual polarization heterodyne
receivers centered at wavelengths of 3, 2, 1.3, and 1.1 mm.
- the 9 pixel dual-polarization heterodyne receiver array,
HERA, operating at 1.3 mm wavelength
- a 1.2 mm bolometer array with 37 or 117 pixels
A scientific project should not be artificially cut into several small
projects, but should rather be submitted as one bigger project, even if
this means 100-150 hours.
If time has already been given to a project but turned out to be
insufficient, explain the reasons, e.g. indicate the amount of time
lost due to bad weather or equipment failure; if the fraction of time
lost is close to 100%, don't rewrite the proposal, except for an
introductory paragraph. For continuation of proposals having led to
publications, please give references to the latter.
A handbook (``The 30m Manual'')
collects much of the
information necessary to plan 30m telescope observations.
It is however outdated in many sections, and we recommend also to
consult the NCS web pages
The report entitled ``Calibration of spectral line data at the IRAM 30m
explains in detail the applied calibration procedure. Both documents can be
retrieved from the
A catalog of well calibrated spectra for a range of sources and transitions
(Mauersberger et al. ) is very useful for monitoring spectral
line calibration. A copy of the 30m file with the calibrated spectra can
be downloaded from the Spanish web site.
The astronomer on duty (whose schedule can be found at URL
../IRAMES/mainWiki/AstronomerOnDutySchedule) should be contacted well
in advance for any special questions concerning the preparation of
an observing run (e.g. setup of on-the-fly maps etc).
Frequency switching is available for both HERA and the single pixel
SIS receivers. This observing mode is interesting for observations
of narrow lines where flat baselines are not essential, although
the spectral baselines with HERA are among the best known in frequency
switching. Certain limitations exist with respect
to maximum frequency throw ( km/s),
backends, phase times etc.; for a detailed report see .
This report also explains how to identify mesospheric lines which may
easily be confused in some cases with genuine astronomical lines from cold
This matter needs special attention as a serious time underestimate may be
considered as a sure sign of sloppy proposal preparation. We strongly
recommend to use the web-based Time Estimator
whenever applicable. Versions 2.6 and higher handle
heterodyne (single pixel and HERA) as well as bolometer observations with
updated instrumental parameters.
If very special observing modes are proposed which are not covered
by the Time Estimator, proposers must give sufficient technical
details so that their time estimate can be reproduced. In
particular, the proposal must give values for , the
spectral resolution, the expected antenna temperature of the signal,
the signal/noise ratio which is aimed for, all overheads and dead
times, and the resulting observing time. The details of the
procedures on which our time estimator is based are explained in a
technical report published in the January 1995
issue2 of the IRAM Newsletter .
Proposers should base their time request on normal
winter conditions, corresponding to 4mm of precipitable water vapor. Conditions during
afternoons can be degraded due to anomalous refraction. The observing
efficiency is then reduced and the flux/temperature calibration is
more uncertain than the typical 10 percent (possibly slightly more
for bolometer observations).
If exceptionally good transmission or stability of the atmosphere
is requested which may be reachable only in
best winter conditions, the
proposers must clearly say so in their time
estimate paragraph. Such proposals will however be particularly scrutinized.
As in previous semesters, we plan to pool the bolometer with other
suitable proposals into a bolometer pool. HERA projects will be
pooled with other less demanding project into a HERA pool. Both
pools will be organized in several sessions, occupying a significant
fraction of the totally available observing time.
The proposals participating in the pools will be observed
by IRAM staff, the PIs and Co-PIs of participating projects and
other cooperating external astronomers. The pool observations will
be organized by the pool coordinators, Stéphane Léon
(bolometers) and Helmut Wiesemeyer (HERA). The participating
proposals are grouped according to their demand on weather quality,
and they get observed following the priorities assigned by the
program committee. The organization of the bolometer observing pool
is described at ../IRAMES/observing/flexible/flexible.html. A description of the HERA
pool will follow soon.
Bolometer and heterodyne proposals which are particularly weather
tolerant qualify as backup for the pool. Participation in the pool
is voluntary, and the respective box on the proposal form should be
Questions concerning the pool organization can be directed to
the scheduler (thumiram.fr) or the Pool Coordinators,
Stéphane Léon (leoniram.es) and Helmut Wiesemeyer
To facilitate the execution of short (8 h) programmes, we
propose ``service observing'' for some easy to observe programmes
with only one set of tunings.
Observations are made by the local staff using precisely laid-out
instructions by the principal investigator.
For this type of observation, we request an acknowledgement
of the IRAM staff member's help in the forthcoming publication.
If you are interested in this mode of observing, specify it as
a ``special requirement'' in the proposal form. IRAM will then decide which
proposals can actually be accepted for this mode.
This observing mode
where the remote observer actually controls the telescope very much like
on Pico Veleta, used to be available from the downtown Granada office, from the
MPIfR in Bonn, from the ENS in Paris, from the OAN in Madrid (near Parque de Retiro), and from IRAM in
Grenoble. However, due to the transition to the telescope's new
control system, remote observing will not be operational during several
months. Observers are strongly encouraged either to consider service
observing for short ( h) and simple proposals, to participate
in a pool, or to come to the telescope.
This section gives all the technical details of observations with the 30m
telescope that the typical user will have to know. A concise
summary of telescope characteristics is published on the IRAM web pages.
The HEterodyne Receiver Array is expected to be
available for most of next winter. Whenever possible, HERA
observations will be pooled. The 9 dual-polarization pixels are
arranged in the form of a center-filled square and are separated by
. Each beam is split into two linear polarizations (after a
successful upgrade in March 2005) which couple to separate SIS
mixers. The 18 mixers feed 18 independent IF chains. Each set of 9
mixers is pumped by a separate local oscillator system. The same
positions can thus be observed simultaneously at any two frequencies
inside the HERA tuning range (210-276 GHz).
A derotator optical assembly can be set to keep the 9 pixel pattern
stationary in the equatorial or horizontal coordinates.
Receiver characteristics are listed in Tab. 1,
and an updated user manual (version 1.9) is available on our
Frequency tuning of HERA, although fully under remote control and automatic,
is substantially more complicated than for the
observatory's other SIS receivers. HERA observers are therefore
advised to send a list of their frequencies to Granada at least 2
weeks ahead of their run.
Recent observations have shown that the noise temperature of the
pixels of the second polarization array may vary across the 1 GHz IF
band. The highest noise occurs towards the band edges which are,
unfortunately, picked up when HERA is connected with VESPA whose
narrow observing band is located close to the lower edge of the 1
GHz band. Therefore, while not as important for wide band
observations with centered IF band, the system noise in narrow mode
is higher (factor 1.5 - 2) as compared to the first
polarization array. We do not recommend
to use the second polarization for frequencies GHz.
HERA can be connected to three sets of backends:
HERA will be operational in two basic spectroscopic observing modes:
(i) raster maps3
of areas typically not smaller than , in
position, wobbler, or frequency switching modes, and (ii)
on-the-fly maps of moderate size (typically ).
Extragalactic proposals should take into account the current
limitations of OTF line maps, as described in the HERA User Manual, due
to baseline instabilities induced by residual calibration errors.
HERA proposers should use the web-based
For details about observing with HERA, consult the User manual.
The HERA project scientist, Karl Schuster (schusteriram.fr),
or Albrecht Sievers (sieversiram.es), the astronomer
in charge of HERA, may also be contacted.
Four dual polarization SIS receivers are available at the
telescope for the upcoming observing season.
They are designated according to the dewar in which they are
housed (A, B, C, or D), followed by the center frequency (in GHz) of their
Their main characteristics are summarised in Tab. 1. All receivers
are linearly polarized with the E-vectors, before rotation in the
Martin-Puplett interferometers, either horizontal or
vertical in the Nasmyth cabin.
Up to four of these eight receivers can be combined
for simultaneous observations in the four ways depicted in Tab. 1.
Note that they cannot be combined with HERA nor with the bolometers.
Also listed are typical system temperatures which apply to normal
winter weather (4mm of water) at the center of the tuning range and
at 45 elevation. All receivers are tuned by the operators
from the control room. Experience shows that it normally takes not
more than 15 min to tune four such receivers.
- VESPA with the following combinations
of nominal resolution (KHz) and maximum bandwidth (MHz):
20/40, 40/80, 80/160, 320/320, 1250/640. The maximum bandwidth can actually
be split into two individual bands for each of the 18 detectors
at most resolutions. These individual bands can be shifted separately
up to MHz offsets from the sky frequency
(see also the sections on backends below).
- a low spectral resolution (4 MHz channel spacing) filter
covering the full IF bandwidth of 1 GHz. Nine units (one per HERA pixel)
are available. Note that only one polarization of the full array is thus
connectable to these filter banks.
- WILMA with a 1 GHz wide band for each of the 18 detectors.
The bands have 512 spectral channels spaced out by 2 MHz.
Several molecules of high astrophysical importance have transitions
in the frequency band 66 - 80 GHz, i.e. between the atmospheric
absorption band and the low frequency edge of the nominal 3mm
tuning range (see Tab.1). Tests have shown that both 3mm
receivers, A100 and B100 have good performance (good upper
sideband rejection and system temperature) in the range 80 - 77
GHz. The receivers become increasingly double sideband
below 77 GHz, until their behavior becomes erratic around 72 GHz.
Due to the rapid variation of the image gain, special care must be
exercised with calibration. A new image gain calibration tool is
provided and described in the test report available on the
IRAM web site
/IRAMFR/PV/veleta.htm). The report includes a set of reference spectra.
Following the considerable demand for this frequency range in the last
2 semesters, the LO hardware has been simplified. As a result,
observations in the 72 - 80 GHz range do not require any special
arrangements. But note that the A230 (B230) receiver is not
available when the A100 (B100) receiver is used below 80 GHz.
Tuning of the single pixel/dual polarization receivers is now
considerably faster and more reproducible than before.
Particular frequencies, like those in the range 72 - 80 GHz or
those near a limit of the tuning range,
may still be problematic. In these cases, we recommend
to check with a Granada receiver
engineer at least two weeks before the observations.
HERA observers, however, are requested to send their frequencies as
soon as their project gets scheduled.
An upgrade of the IF polarimeter 
is now available,
where the cross correlation between the IF signals from a pair of orthogonally
polarized receivers is made digitally in VESPA.
The new observing procedure, designated XPOL, generates simultaneous
spectra of all 4 Stokes parameters. The following combinations of
spectral resolution (kHz) and bandwidth (MHz) are available:
40/120, 80/240, and 320/480.
Although successful XPOL observations were made at many frequencies,
experience is still limited, particularly at 1.3mm wavelength and
with respect to observations of extended sources.
Considerable progress was made in reducing polarization sidelobes, notably
for Stokes V. Interested users should contact C. Thum for details.
Data reduction software using CLASS enhanced with a
graphical user interface is available (H. Wiesemeyer,
wiesemeyiram.fr). A short guide
(at ../IRAMFR/PV/veleta.htm) describes XPOL observations.
Polarimetry proposals for observation of extended sources should demonstrate
that their observations are feasible in the presence of the known
sidelobes (see ).
The bolometer arrays, MAMBO-1 (37 pixels) and MAMBO-2 (117 pixels),
are provided by the Max-Planck-Institut für Radioastronomie. They
consist of concentric hexagonal rings of horns
centered on the central horn. Spacing between horns is .
Each pixel has a HPBW of 11.
We expect that MAMBO-2 will be normally used, but MAMBO-1 is kept as
The effective sensitivity of both bolometers for onoff observations is
mJys for mapping. The rms,
in mJy, of a MAMBO-2 map is typically
where , in arcsec/sec, is the velocity in the scanning
direction and , in arcsec, is the step size in the
orthogonal direction. The factor is 1 (2) for sources of size
. It is assumed that the map is made large enough
that all beams cover the source.
The sensitivities apply to bolometric
conditions (stable atmosphere),
0.3, elevation 45 deg, and application of skynoise filtering algorithms).
In cases where skynoise filtering algorithms
are not or not fully effective
(e.g. extended source structure, atmosphere not sufficiently stable),
the effective sensitivity is typically about a factor of 2 worse. For
those projects, only atmospheric conditions with
low skynoise (i.e. stable atmosphere, no clouds,
little turbulence) are recommened unless the
expected signal is about 1 Jy/beam or stronger.
The bolometer arrays are mostly used in two basic observing modes, ON/OFF and
mapping. Previous experience with MAMBO-2 shows that the ON/OFF reaches
typically an rms noise of mJy in 10 min of total observing time
(about 200 sec of ON source, or about 400 sec on sky integration time)
under stable conditions.
Up to 30 percent lower noise may be obtained in perfect weather.
In this observing mode, the noise integrates down with time as
to rms noise levels below 0.4 mJy.
In the mapping mode, the telescope is scanning in the
direction of the wobbler throw (default: azimuth) in such a way
that all pixels see the source once.
A typical single map4
with MAMBO-2 covering a fully and homogeneously sampled area of
(scanning speed: per sec, raster step: )
reaches an rms of 2.8 mJy/beam in 1.9 hours if skynoise filtering is effective.
Much more time is needed (see Time Estimator) if sky noise filtering cannot be
The area actually scanned (
) must be larger than the map size
(add the wobbler throw and the array size (), the source extent,
and some allowance for baseline determination)
if the EHK-algorithm is used to restore properly extended emission.
Shorter scans may lead to problems in
restoring extended structure. Mosaicing is also
possible to map larger areas. Under many circumstances,
maps may be co-added to reach lower noise levels.
If maps with an rms
mJy are proposed, the proposers should
contact R. Zylka (zylkairam.fr).
The bolometers are used with the wobbling secondary mirror
(wobbling at a rate of 2 Hz).
The orientation of the beams on the sky changes with
hour angle due to parallactic and Nasmyth rotations, as the array is
fixed in Nasmyth coordinates and the wobbler direction is fixed with
respect to azimuth during a scan.
Bolometer proposals participating in the pool have their observations
(maps and ONOFFs) pre-reduced by a data quality monitor
which runs scripts in MOPSIC. This package, complete with all necessary scripts,
is also installed for off-line data analysis in Granada
and Grenoble. It is also available for distribution from the IRAM Data Base for
Pooled Observations or directly from R. Zylka (zylkairam.fr).
The older software packages (NIC  and MOPSI)
are still available, but cannot process data obtained with the NCS.
Bolometer proposals will be pooled together like in previous
semesters along with suitable heterodyne proposals as long as the respective
The web-based time estimator handles well the usual bolometer observing
modes, and its use is again strongly recommended. The time estimator uses
rather precise estimates of the various overheads which will be applied
to all bolometer proposals.
If exceptionally low noise levels are requested which may be reachable only
in a perfectly stable (quasi winter)
atmosphere, the proposers must clearly say so in their time estimate
paragraph. Such proposals will however be particularly scrutinized.
On the other extreme, if only strong sources are observed and moderate
weather conditions are sufficient,
the proposal may be used as a backup in the observing pool. The
proposal should point out this circumstance, as it affects positively the
chance that the proposal is accepted and observed.
Table 2 lists the size of the telescope beam for the
range of frequencies of interest. Forward and main beam efficiencies
are also shown (see also the note by U. Lisenfeld and A. Sievers, IRAM
Newsletter No. 47, Feb. 2001). The variation of the
coupling efficiency to sources of different sizes can be estimated from
plots in Greve et al. .
At 1.3 mm (and a fortiori at shorter wavelengths) a large
fraction of the power pattern is distributed in an error
beam which can be approximated by two Gaussians of FWHP
and (see  for details).
Astronomers should take into account this error beam when converting
antenna temperatures into brightness temperatures.
A variable and sometimes large contribution to the error beam was known
to come from telescope astigmatism.
Extensive work during the last years had shown that the astigmatism resulted
from temperature differences between the telescope backup structure and
the yoke. The recent installation of heaters in the yoke by J. Peñalver
has nearly completely removed the astigmatism.
Main observational parameters of 30m telescope.
- beam width (FWHP). A fit to all data gives:
/ frequency [GHz]
- forward efficiency (coupling efficiency to sky)
- main beam efficiency. Based on a fit of measured data to
the Ruze formula:
With the systematic use of inclinometers the telescope pointing became
much more stable. Pointing sessions are now scheduled at larger intervals.
The fitted pointing parameters typically yield an absolute rms pointing
accuracy of better than . Receivers are closely
aligned (within ).
Checking the pointing, focus, and receiver alignment is the
responsibility of the observers (use a planet for alignment checks).
Systematic (up to 0.4 mm) differences between the foci of various receivers
can occasionally occur.
In such a case the foci should be carefully monitored and a compromise value
be chosen. Not doing so may result in broadened and
distorted beams ().
Unnecessarily large wobbler throws should be avoided, since they introduce
a loss of gain, particularly at the higher frequencies, and imply a loss
of observing efficiency (more dead time).
- Beam-throw is depending on wobbling frequency.
At 2 Hz, the maximum throw is
- Standard phase duration: 2 sec for spectral line observations, 0.25 sec
for continuum observations.
The following four spectral line backends are available which can be
individually connected to any single pixel receiver and, if indicated,
also to HERA.
The 1 MHz filterbank consists of 4 units. Each unit has 256
channels with 1 MHz spacing and can be connected to different or
the same receivers giving bandwidths
between 256 MHz and 1024 MHz. The maximum bandwidth is available
for only one receiver, naturally one having a 1 GHz wide IF bandwidth.
Connection of the filterbank in the 1 GHz mode presently excludes the
use of any other backend with the same receiver.
Other configurations of the 1 MHz filterbank include
a setup in 2 units of 512 MHz connected to two different receivers, or 4 units
of 256 MHz width connected to up to four (not necessarily) different receivers.
Each unit can be shifted in steps of 32 MHz relative to the center frequency
of the connected receiver.
The 100 kHz filterbank consists of 256 channels of 100 kHz spacing.
It can be split into two halves, each movable inside the 500 MHz IF
bandwidth, and connectable to two different single pixel receivers
(must be set up in narrow band mode).
VESPA, the versatile spectrometric and polarimetric array,
can be connected either to HERA or to a subset of 4 single pixel receivers,
or to a pair of single pixel receivers for polarimetry.
The many VESPA configurations and user modes are summarized in a
 and in a
but are best visualised on a demonstration program which can be downloaded
from our web page
at URL ../IRAMFR/PV/veleta.htm.
Connected to a set of 4 single pixel receivers VESPA typically provides up to
12000 spectral channels (on average 3000 per receiver).
Up to 18000 channels are possible in special
configurations. Nominal spectral resolutions range from 3.3 kHz
to 1.25 MHz. Nominal bandwidths are in the range 10 -- 512 MHz.
When VESPA is connected to HERA, up to 18000 spectral channels can be used
with the following typical combinations
of nominal resolution (kHz) and maximum bandwidth (MHz):
20/40, 40/80, 80/160, 320/320, 1250/640.
The 4 MHz filterbank consists of nine units.
Each unit has 256 channels (spacing of 4 MHz, spectral resolution at 3 dB
is 6.2 MHz) and thus covers a total bandwidth of 1 GHz.
The 9 units are designed for connection to HERA, but a subset of 4 units
can also be connected to the backend distribution box which feeds
the single pixel spectral line receivers. All these receivers have a 1 GHz RF
bandwidth except for A100 and B100 (500 MHz only).
At the present time, a 4 MHz filterbank cannot be used simultaneously with
the autocorrelator or the 100 kHz filterbank on the same receiver.
The wideband autocorrelator WILMA consists of 18 units. They can
be connected to the 18 detectors of HERA. Each unit provides 512
spectral channels, spaced
out by 2 MHz and thus covering a total bandwidth of 1 GHz. Each band is sliced
into two 500 MHz subbands which are digitized with 2 bit/1 GHz samplers.
An informative technical overview of the architecture is
available at URL
Note that WILMA cannot presently be connected to any of the
single pixel receivers.
Up: IRAM Newsletter 67 (August 2006)
Previous: Proposals for IRAM Telescopes