>Is the Mopra 20-cm receiver for VLBI? With Parkes still going, at least >part-time at that frequency, I don\'t see any other need for it. And, how >much does it get used?
Yes, the 20/13 and 6/3 cm receivers at Mopra are used exclusively for VLBI, with Mopra being an important part of the LBA network. There have traditionally been three week-long VLBI sessions each year, though we are moving towards shorter but more frequent sessions, partly in response to demand for more frequent VLBI monitoring of sources. The large majority of VLBI observations to date has been done in the 20/13 and 6/3 cm bands. In recent years, the 20-cm band has been used for about 1/3 of the observations - mainly pulsar and OH spectral line projects.
>With such things as the Christmas week shutdown, the reduced response >to maintenance calls, etc. you are certainly cutting down the total time >available on all instruments. That may be necessary but what is the >estimated fraction of time that would be lost and what is the current >oversubscription?
The main reduction in observing time will be the Christmas week (about 2%). The changes proposed for the maintenance schedule are to streamline the way maintenance is done - but the overall number of maintenance days will be about the same. The reduction in time from less support during night time should be small - though at the Compact Array it may mean, for example, that some observations are taken with fewer dishes for some hours. We have been fortunate the last two years in being able to schedule two large projects over the Christmas/New Year period with experienced teams that have been quite self-sufficient, enabling the majority of observatory staff to take a well-earned break. It will not always be possible to do this, and providing support for observations when there are many changes between observing teams has obvious implications for observatory staff.
The over-subscription rate is typically 1.5 - 2.0 on the ATCA and 1.2 to 1.7 on Parkes. For Parkes the oversubscription rate for Galactic sidereal times only is typically 2.0.
>There must be some time available for short-spacing arrays at cm >wavelengths on the compact array - they cannot be only for the mm >observations - as almost all Galactic, Magellanic Cloud, and objects >within other galaxies are either extended ar lie in complex extended >regions and we need to evaluate the smoothly distributed emission.
In the future, we plan to have fewer reconfigurations at the Compact Array. This may mean that compact configurations are only provided during the winter season - for both mm and cm observing. However, before this decision is made, the impact of this will be assessed against the scientific demand for compact configurations in the summer season.
(With thanks to Jessica Chapman for assistance in this reply)
