1. Program description
The purpose of this program is to provide an estimation of the observing
time required at the IRAM 30m telescope for a given type of spectral line or continuum
observation. The formulas used in this Time Estimator are described in the the
corresponding Description Report
(see also the Jan. 95 Newsletter
and the 30m Manual ). The
most recent values of the telescope and receiver parameters are used.
The Time Estimator in its updated version handles three types of spectroscopic
observations where (i) one or more sources are observed with the same set of
frequencies, (ii) one source is observed with up to five different sets of frequencies,
and (iii) one or more sources are observed with the MPIfR Bolometer.
This tool works through several fill-out forms containing the parameters we consider as necessary to estimate the telescope time at the moment of a proposal writting. It uses two connected web pages and offers the possibility to quickly have an idea of the way any parameter may change the integration or total telescope time. By that way, we also hope this tool could help observers who don't have a good experience of the 30m to get more familiar with the telescope.
-[NEW]- We now provide time estimates for the new dual receivers C and D (see August 99 Newsletter ). Since their installation is planned for October 99, no experience in operating these frontends exists at the time of writing. Anyhow, the Time Estimator might be updated to better account for further information on the receiver perfomances.
2. First observation type
When the first page is complete, the [Int. time calculation] button allows to compute the required integration time for every chosen receiver.
It simultaneoulsy displays on the second page some warning/advise messages and gives an estimation of the total telescope time (i.e. observation of all the sources) by considering default values for the observing mode parameters. You can change those values and resubmit the complete calculation with the [Obs. time calculation] button located at the bottom of the second page. When you are satisfied with the calculation, a LaTeX file containing the main results is generated with the [LaTeX file generation] button. You can include it in your proposal. - We now also give
the r.m.s. reached by all the receivers others than the one whose int. time
leads the calculations.
For special features associated to this case, see Chapter 7
Please note that any of the submitted parameters will be applied to all the sources of your project (ie no distinction in sky elevation, line strength, line width...)
The complete results displayed on the second window account for all the sources and sometimes the total time may be much higher than the one of a typical uninterrupted observing session (say 8-12 hours). Since we consider only one tuning for the run (as if the run could be done without leaving the telescope to another project), the total observing time requested should be increased by a certain number of "tuning times". See the overheads and deadtimes section to know about the time it corresponds to.
3. Second observation type
When the first window is complete, the [Int. time calculation] button allows to compute the required integration time for every chosen receiver of each set. It simultaneoulsy displays on the second window some warning/advise messages and gives an estimation of the total telescope time for all the sets by considering default values for the observing mode parameters. You can change those values and resubmit the complete calculation with the [Obs. time calculation] button located at the bottom of the second window. When you are satisfied with the calculation, a LaTeX file containing the main results is generated with the [LaTeX file generation] button. You can include it in your proposal.
Consequence: In case of velocity smoothing, the Time Estimator uses the frequency bandwidth corresponding to the lowest frequency for each receiver occurring in the 5 sets.
4. Bolometer observation -[NEW]-
When the first page is complete, the [Obs. time calculation] button allows to compute an estimation of the total required telescope time for the run. It simultaneoulsy displays on the second page some warning/advise messages. When you are satisfied with the calculation, a LaTeX file containing the main results is generated with the [LaTeX file generation] button. You can include it in your proposal.
First Page Parameters:
For special features associated to this case, see Chapter 7
Please note that some parameters, such as the complete backend configuration per receiver, and the observing mode, are the same for all frequency sets, this to avoid a too complex management of the program.
The first table on this page deals with the integration time required with each of the selected receivers to reach the requested r.m.s. Then, some warning/advise messages will appear with respect to the results and according to our experience with such observations. The boxes displayed on this page handle some parameters of the observing mode (check special features of On-The-Fly mode). We use default values for all parameters to allow complete calculation on the first submit. But you can modify those parameters to your own observing goals and recompute the results. The last table breaks the total telescope time down into several tasks and gives the overall observing efficiency (ON source integration time over total telescope time). For the estimation of overheads and deadtimes, see the corresponding section.
Please note that any of the submitted parameters will be applied to all the sources of your project (ie no distinction in sky elevation, source strength, source size...)
- On-the-fly parameters:
Second Page Parameters:
The second page, displayed on the second window, gives a description of the time partition corresponding to the computed run. For the details about the way this is done, see the overheads and deadtimes section.
We would like to insist on the fact that the observers should be very carefully with the requested sizes of the maps. Indeed, long scan will suffer from field rotation and bad baseline. To avoid this problem, smallest maps can be done separatly. Since the program can not "cut" maps by itself, the observer shall submit two "sub-maps" and add himself the times required for the proposal.
5. Observing mode parameters
Each time the results page is displayed, boxes containing the observing mode parameters are shown with default values. As follow, we give a description of those parameters for each mode. Some of them are not required in the fill-out form and appear in bold with the default value we assign to them.
- Wobbler Switching parameters:
- Frequency Switching parameters:
- Spectral Line On-The-Fly parameters:
For this mode, the number of possibilities and observing strategies has become so important in the latest times that the observing sequence we consider can sometimes look simple compared to what you really want to do. However, we think that this is still consistent in terms of time estimation for a map of a given size with a given scanning step. Anyhow, don't hesitate to contact us for questions or doubts you may have.
The results of the total telescope time calculation are displayed in a table giving how this time is parted between the preparation and observing phases. The way the overhead and deadtimes are estimated is the following:
Heterodyne:
- Tuning time: After installation of new receivers C and D, all frontends should be automatically tunable from the control room. From our experience of receivers A and B, we consider a constant time of 20 minutes to tune up to 4 receivers simultaneously. This includes calibrations done just after the tuning (checks).
- Preparation time: A constant preparation time of 20 min. is considered for the first slew to the source and the calibration on a line calibrator. In case of several frequency sets, it decreases to 15 min. because we assume that we are already close to the source (what is not always the case when you start a run).
- Pointing/Focus/Calibration time: Two
types of pointing are considered: on a strong (far ?) source, with a focus, and on a weaker source close to the target. The first type of pointing
is done every 3 hours if 1mm receivers are used, every 6 hours if not, and the second every 2 hours. Finally,
calibrations are done before each scan for psw, fsw, wsw and raster, and every 10 minutes for OTF.
Bolometer:
- Pointing/Focus/Calibration time:
A typical bolometer observing run is assumed to include a pointing near the target source every 1 hour,
a pointing and a focus on a strong source every 1.5 hours,
a bolotip every 1.5 hours
and a pointing, focus, and a onoff measurement on a calibrator every 2 hours
-----> To simulate the effective time gain of the smooth, one would then have to enter the final requested r.m.s. want multiplied by the sqrt of the size ratio applied between the original and final sampling.
Example: Say you map a source with original 4"*4" pixels. You aim to smooth to a 12"*12" grid. The ratio is then 9. If you need a noise of 0.05K in the final sampling, the input of the form should be 0.15K If you had required 0.05K per main beam, the time would have been 9 times larger.
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