Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/management/atuc/2005jun/docs/3.3_ATUC_tid.doc Дата изменения: Wed Jun 8 09:34:03 2005 Дата индексирования: Sun Jun 27 06:09:27 2010 Кодировка: Поисковые слова: universe

ATNF ATUC Memorandum

To: ATUC
From: Jim Lovell
Date: 2005 June 3
Subject Tidbinbilla report

1. 70m Observing statistics for Jan to July 2005.

Currently there are 8 active proposals and observations have been
completed for 2 of these. Three proposals are for zero-spacing maps to
support ATCA observations. A status summary of proposals is available
on the ATNF web pages and is regularly updated.


Between January and July 2005, a total of 441 hours was allocated to
radio astronomy activities on the 70m. Of this, 280 hours was
allocated for Host Country (ATNF) use, the remainder being used for a
water megamaser survey lead by Lincoln Greenhill, and for NASA-
scheduled VLBI experiments. The 280 hours of Host Country time was
used as follows:
. VLBI (LBA): 40 h
. Spectroscopy: 240 h

2. 70m Antenna Maintenance.

From July 18 until January 2006, the 70m will undergo maintenance on
the azimuth bearing and the antenna controller hardware will be
upgraded. No observations will be possible during this time.
Tidbinbilla proposals submitted for the 2005APRS deadline will remain
active for 18 months rather than the usual 12 to compensate.


3. Tidbinbilla Support.

In order to spread the support load it has been proposed that a few
Tidbinbilla DAs be appointed to help carry out service observations
and other support work. As an initial step, Erik Muller will be
spending some time on Tidbinbilla support this year.


4. Development.

The most limited resource at Tidbinbilla is observing time, granted to
us by NASA. Therefore development work is aimed at getting the most
science out of the available time by improving observing efficiency.
In the past, this work has included increasing the instantaneously
accessible bandwidth to allow more spectral lines to be observed
simultaneously and improving the observing software to reduce
overheads.


There are two main development tasks currently underway. The first is
an implementation of on-the-fly (OTF) mapping. This will improve the
efficiency of mapping and antenna pointing measurements over the
current point-by-point method. The second is an upgrade to the 12mm
system on the 70m from one to two channels. The upgrade will allow
dual polarisation observations, improving sensitivity by a factor of
sqrt(2) and halving the integration time required to reach a given
sensitivity limit.


. OTF Mapping.

As reported at the last ATUC meeting, attempts to implement OTF
mapping have proved unsuccessful to date due to limitations in
DSN software. The software updates that will be necessary as a
result of the 70m upgrade may allow OTF mapping to be achieved.
We are also looking into alternative methods that may allow OTF
mapping and do not require the DSN software.


Meanwhile, tests of gridded mapping have recently been carried
out. Observations of a 5x5 grid in support of Cormac Purcell's
proposal T014 have been combined with ATCA data and have
demonstrated that mapping is possible in this mode. The
procedure for reducing this type of data has been documented and
will be made available to users.


. 12mm dual polarisation upgrade.

With the help of Graham Moorey, the upgrade of the 12mm system
from single to dual channel is progressing well. A schematic of
the second signal path has been prepared and the necessary
components required are being obtained. Installation and testing
will be carried out during the 70m downtime and it is expected
that dual polarisation observations will be possible when it
returns to service in January.


5. 34m beam-waveguide antenna DSS34.

For many years NASA have been allocating observing time on the 34m
antenna DSS45 as well as the 70m. DSS45 is restricted to the 3 and
13cm bands only and therefore there has been no interest in using this
antenna as a single dish. Also less time is allocated than on the 70m
(about 60h per year). However it has been used for some continuum VLBI
observations.


Earlier this year a co-axial 8.4 and 32 GHz system was installed on
the 34m beam-waveguide (BWG) antenna DSS34. The main purpose of this
new system is spacecraft tracking but it may also be of some limited
use to radio astronomy. Also the design of the antenna permits the
installation of many more receiver systems and room has been set aside
for radio astronomy. With the upgrade of the ATCA and Mopra to 7mm
systems, a similar capability at Tidbinbilla will be important for LBA
observations in this band. (It is worth noting that the DSS34 is
designed to work up to frequencies of 100 GHz with the inner 26m
diameter illuminated). Therefore a request has been made for the DSN
to switch radio astronomy allocations from DSS45 to DSS34.


A further advantage of this switch is that the antenna controller on
DSS34 is of the same type to be installed on the 70m. Therefore the
70m downtime can be used to update and test observing software,
including OTF mapping, on DSS34.


At this stage, given the need for test time and the likely limited
scientific usefulness of the 32 GHz system, there are currently no
plans to offer the 34m to users. This issue will be revisited after
the 70m downtime when ATUC may wish to consider whether users would
like access and if the installation of additional receivers is
desirable.


Specifications of the 32 GHz system on DSS34 are as follows:
. Frequency range: 31800 to 32300 MHz
. Dual polarisation (RCP and LCP)
. 60% aperture efficiency
. Beam FWHM = 61"
. Tsys above atmosphere = 23 K. Typical Tsys with atmosphere = 30
K.
. SEFD = 160 Jy. (Compare to an expected sensitivity of 5 ATCA
antennas at 32 GHz of 150 Jy).

6. Miscellaneous

A new web-based sensitivity calculator is now available to help in
proposal preparation. It can be found on the Tidbinbilla page on the
ATNF site http://www.atnf.csiro.au/observers/tidbinbilla.