Time assignment information
Compact Array scheduling
With the installation of the 3- and 12-mm systems on the Compact Array, the requested use of the telescope in the last two terms/semesters has increased substantially. This is a great mark of success, and a gratifying result to all of those involved in the millimetre upgrades. As a result of the increased interest, observing time on the Compact Array has become more competitive. This is particularly so during the millimetre season. Observers may care to take the following into account when making proposals.
Over-subscription factors
In the 2004 May term, the oversubscription factor on the ATCA was approximately 3:1. Over one third of the time requested was with the new 3- and 12-mm systems. The oversubscription for the 2004 October semester was 2:1. The ATNF time assignment process ranks each proposal on the merits of its scientific objectives and its technical feasibility. The best proposals are scheduled, with the constraints of the very best used to help dictate some operational parameters (mainly the timing of array configurations within the term/semester). The higher oversubscription rates have meant that some good proposals that would have previously been awarded time have been unsuccessful. With the introduction of the full mm-systems, it is expected that the "millimetre season", from May to October, will remain significantly more popular and oversubscribed than the months of November-April. Time requested in this period will be more competitive.
(Note that the millimetre season is also the time that the Galaxy is a night time object, and so is also popular with Galactic spectral-line observers.)
Coordinated observations
The Compact Array is regularly scheduled in coordinated simultaneous observations with other telescopes such as satellites. For the proposers of these experiments, organising such multiple telescope proposals is often a complex undertaking. Scheduling is often an iterative affair. For the Compact Array it is somewhat more complex to schedule coordinated observations during the millimetre season than at other times. One aspect to consider is that coordinated experiments often target compact objects, and thus tend to prefer the 6-km configurations. However millimetre proposals tend to prefer compact configurations. In general the availability of 6-km arrays in the millimetre season will be more limited.
Proposers of coordinated experiments may wish to try to organise their observation when there is less chance of conflicting requirements.
Millimetre scheduling
The Compact Array can make scientifically good observations at centimetre wavelengths in almost any weather conditions except severe thunderstorms and high winds. However, good weather is essential for 3-mm observations. Typically, about 30% of time during the millimetre season is unsuitable for 3-mm observations. To give 3-mm proposals some added robustness to poor weather, a "swap scheduling" scheme has been used. Under this scheme, a partnering centimetre project is scheduled about two days after a 3-mm project. On the day of the 3-mm observing, in case of poor weather, a project can be swapped with the partnering centimetre proposal.
To simplify swaps for the centimetre observers, service mode observing is offered to suitable centimetre projects.
For the swap system to work there needs to be sufficient centimetre proposals to swap with the 3-mm proposals. However to date, the array configurations popular with millimetre observers (H75, H168 and EW214) have not proven popular with centimetre observers. In the 2004 millimetre season there were insufficient swap projects.
Observers are advised that there is potentially a significant amount of centimetre time available during the millimetre seasons for swap projects that require compact configurations. We encourage observers to consider science which can make effective use of this option. Large centimetre projects that could be used as "backups" during poor weather are also encouraged.
Bob Sault
(Bob.Sault@csiro.au)