Atacama Pathfinder EXperiment APEX
Observing with APEX
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Observing with APEX


APEX is a 12 meter radio telescope built by an international collaboration involving the Max-Planck-Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and ESO; operations are entrusted to ESO. The observing time is shared as follows: Max Planck Institutes and German universities receive 49.5%, ESO receives 28.8%, OSO receives 11.7% and Chile 10%.

The Annual variation of the Precipitable Water Vapour (PWV) at the APEX site is shown in the figure below.

"Figure 1. Left: Annual variation of the Precipitable Water Vapour (PWV) content at Chajnantor, based on historical observations with the APEX radiometer recorded in the last 9 years. Blue, green and red histograms indicate the 25, 50 and 75 percentile levels, respectively. The yearly APEX science operations period from 20 March till 20 December is scheduled to avoid the worse conditions during Altiplanic winter; Right: Historical cumulative plot showing the fraction of days with PWV contents below a certain value. Only observations collected during the science operations periods are considered in this plot."

Applying for observing time

Performing observations with APEX

Observations at APEX are normally done in service mode. For questions, please contact the APEX Head of Science Operations, Francisco Montenegro, email: fmontene(at)

Once you proposal is accepted, you need to prepare the observations. This basically means you need to inform the APEX staff about everything which is important for carrying out your observations, including source coordinates, receiver setup, possible pointing sources, observing procedures, etc.

Reducing APEX data

The APEX raw data are in the so-called MB-FITS data format. For line observations, these raw data are calibrated on-line by the OnlineCalibrator program, which writes the calibrated spectra (TA* scale) into a CLASS-format data file. The data can be further reduced and analyzed using for example CLASS and GRAPHIC or MAPPING program of the GILDAS software package.

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APEX End of mission report

Please take some minutes to evaluate your observing mission at APEX using this form. Thanks!