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.
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.
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.
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.
4. Bolometer
observation
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.
| 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...) |
|---|
First
Page 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:
- 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.
In case of bolometer observations, this differs for On-the-fly mapping since
the map can not be stopped to achieve pointings inbetween. Instead of that,
we consider 1 [pointing-focus-calibration(bolotip)] before each map.
For On-off, we assume a calibration every hour.
-----> 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.