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
a backup.
The effective sensitivity of both bolometers for onoff observations is
mJys
and
mJys
for mapping. The rms,
in mJy, of a MAMBO-2 map is typically
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 map4with 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
used.
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 (zylka@iram.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 (zylka@iram.fr). The older software packages (NIC [7] and MOPSI [8]) 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 PIs agree. 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.