At a time when the receiver hardware at the 30-m telescope undergoes rapid and profound changes, it becomes difficult to prepare adequately an observing session. A Time Estimator tool, which incorporates the most recent receiver and telescope parameters was written to help the preparation of spectral-type observations. This tool may be especially useful for observers unfamiliar with the IRAM 30-m telescope.
The Time Estimator, which is available on the IRAM web pages in Spain and France (http://iram.es, http://iram.fr), provides a realistic estimate of the total telescope time needed to reach a specified rms noise in a particular observing mode with a specified receiver and backend configuration. In the final output table (an example is shown in Fig. 8), the total telescope time is broken down into several essential components, and the overall observing efficiency (ON source integration time over total telescope time) is calculated.
Figure 8: Final output table of the Time Estimator.
Since up to 4 receivers can be used simultaneously on the 30m telescope and since many observing modes are available, the number of ways to observe is very large. In order to keep the Time Estimator manageable and attractive the tool currently handles only the two most used types of spectroscopic observations, namely (i) observations of a number of sources with one single set of frequencies and (ii) observations of one source with several (up to five) frequency sets. All the main observing modes (position switching, wobbler switching, raster mapping, frequency switching, and on-the-fly) are available. The optical compatibility of the requested receivers is checked, and the losses due to the Martin-Puplett interferometers at the specified frequencies are explicitly taken into account. Allowance is made for all relevant dead times, including telescope slew times, pointing, focus, and hot-cold calibrations. The typical time needed for the tuning of the receivers and a minimum of related checks is also taken into account.
The Time Estimator takes input from several templates such as the one shown in Fig. 9. Convenient links to an extensive help page are provided. Input and output are on two separate, but connected web pages. Switching back and forth between these pages allows a rapid optimization of the observational parameters for a given telescope time. A very compact summary text (in LaTeX) can be generated at the end for possible inclusion in a proposal.
A further version of the Time Estimator which covers continuum-type observations with the bolometer array is planned. In the meantime, it is hoped that the current version is widely used and found useful and that the gross underestimations of the observing time occasionally made by observers will be avoided. Please, send your comments on the current version 1 of the Time Estimator to the undersigned (David Teyssier).
Figure 9: Main input table of the Time Estimator.
David Teyssier
In response to questions from observers, and to complement the time estimator described above, the receiver group has prepared some general information about the MPI diplexer that is used with the new dual-channel receivers.
The essential features of the diplexer are described in a short MPI Guide that can be found from the iram.fr web page by going to Technical activities, then to Receiver group. A MPI simulator is also provided. The essential points worth mentioning here are:
, giving 15% diplexing loss;
, giving 5% diplexing loss.B.Lazareff