EMIR Efficiency Calculator
This tool permits a quick and accurate estimate of the attainable observing efficiency, once the observing sequence starts, for a given set of user parameters for both STARE_IMG and LS/MOS observing modes. It makes use of fixed time delays for the offsets between dither points and between sky and object pointings. Time to point the telescope and acquire the source, as well as other overheads are not accounted for. The actual duration of the observation cannot be computed with this tool. Total observing overheads must be obtained following the guidelines provided by GTC. Following is a short description of the observing configuration parameters:
- On source exposure time. This is the total on source time requested for the observation, in seconds. It can be given as a single figure or as a time range. In the latter case, the full range will be scanned in search for the best configurations.
- Maximum and minimum single exposure time, in seconds. These apply to the single exposure times in the observing sequence and they are figures that supersede the default values and must be used with extreme caution. Specifically, large values for Tmax can result in overrun of the predefined coherence time, hence make it difficult the correct background subtraction. It is strongly advised to leave these values as 0 or blank, which will result in using the default values. Currently, the use of this setting at the GTC is still being considered, so users should not rely on them.
- Filter or grism, to specify both the observing mode - either img or spec - and spectral band.
- Dither points: number of pointing positions within each cycle. Either 1 (no dither), 4 (as for ABBA in spec) or 7.
- Separated sky. Bear in mind that if separated sky observations are requested, the same observing configuration than that for the target object will be repeated for the sky frames, hence doubling the observing time.
In the results, the optimal configuration is given on top, with values for Niter, number of cycles; Nexp, number of exposures per pointing position; and Tdith, exposure time per exposure.
Below the optimum configuration, which will be set by the EMIR Control System if the input parameters are given, up to 10 different configurations, sorted in decreasing efficiency, are given. Some of these might have higher efficiency than the selected optimum, but with different total exposure time, hence permitting to refine the requested configuration.