Atacama Pathfinder EXperiment APEX
Observing with APEX


APEX observing system

Facility instruments

    Instrument Type Usage Frequency [GHz] HPBW # of pixels Location Status Comment
    APEX-2A Heterodyne Facility 279 - 381 18" 1 Nasmyth-A ok  
    LABOCA Bolometer array Facility 345 18" 295 Cassegrain X a separate call for proposals will be announced
  • APEX-2A

    APEX-2A is a heterodyne receiver remotely tunable in the range 279-381GHz. It is a double-sideband (DSB) receiver with typical receiver temperatures of Trec=60-80 K. Under good weather conditions, this leads to DSB system temperatures of ~150 K over most of the tuning range, but up to 250 K towards 370 GHz.


    The Large Apex BOlometer CAmera is a 295-pixel, 870 µm bolometer array under construction at MPIfR.
    More information: LABOCA Fact Sheet (pdf)

  • Future facility instruments

    In the future APEX will be equipped with SIS heterodyne receivers covering the bands at 211 - 275 GHz, 275 - 370 GHz, and 385 - 500 GHz, a heterodyne HEB receiver operating at 1.25-1.39 THz as well as a bolometer array operating at 350 µm. More information: APEX Facility Heterodyne Receivers Fact Sheet (pdf)

PI instruments

Apart from the facility receivers, PI instruments will be installed at APEX during longer or shorter time periods. Some of them can be used by the community in collaboration with people from the corresponding PI group. In case of the MPIfR instruments, contact Rolf Güsten (rguesten(at) before submitting any proposals.

    Instrument Type Usage Frequency [GHz] HPBW # of pixels Location Status Comment
    FLASH Heterodyne PI (MPIfR) 430 - 492 14" 1 Nasmyth-A ok  
    Heterodyne 780 - 887 7" 1 ok  



    FLASH is a dual channel DSB receiver, with one channel covering the 460 - 495 GHz range, and the other one the 790 - 840 GHz range with typical Trx (DSB) = 200 K and 400 K, respectively. For time estimates, proposers should assume system temperatures of 650 K and 2000 K, respectively, for good weather conditions (1 mm precipitable water vapour, 80 degrees elevation).

    More information: FLASH Fact Sheet (pdf)

  • Future PI instruments



    The facility Fast Fourier Transform Spectrometer consists of two units with a bandwidth of 1GHz each. Both units are configurable to provide up to 16384 spectral channels, thus providing a spectral resolution of up to 61kHz. The two units can be connected to one receiver each, or the two units can be configured to produce a single backend with 2 GHz bandwidth. FFTS Fact Sheet (pdf)

Observing modes

    • Spectral line observations

      • Switch modes:
      • Position switching

        In position switching mode the telescope moves between the ON-position and a user-defined reference position. Since APEX can move very fast, stable baselines can be achieved under normal weather conditions. The reference position can be given in relative coordinates (to the catalog source position) or in absolute coordinates, in the horizontal or equatorial system. Integration times at ON- and OFF-positions can be different, and a number of ON-positions can be observed using one OFF-position.

        • Future switch modes (not yet implemented )

          • Beam switching (using the wobbling secondary)

          • Frequency switching

      • Observing modes:


        Observations of a single position in any of the available switch modes.

        Raster map

          In raster mapping the telescope moves through a grid defined by the user, and any of the available switch modes can be used. The extent of the raster map is specified and spacings between raster points are also specified. The coordinate system can be either equatorial (RA and Dec) or horizontal (Az and El). The number of observed points per reference point can be specified (with automatic adjusting of integration times in the reference point). Calibrations cannot currently be performed during a raster map.

        On- The-Fly mapping (OTF)

        The On-The-Fly mapping procedure allows to scan continuously along one direction in a rectangular map while writing out data after given time intervals, thus saving the overhead between subscans that occurs for rasters. Otherwise the parameters are identical to that of the raster. The spacings along the scanning axis should thus not exceed about one third of the beam to avoid beam broadening. Due to technical reasons currently an OTF integration time of exactly one second is recommended. Please note that the APEX 2a observing time calculator is not yet prepared for OTF observing time estimates

    Bolometer observations

The bolometer arrays will have various observing modes, including on-the-fly mapping in rectangular, circular and spiral patterns.

In addition to the observing modes listed above, various standard procedures are used for calibration purposes, like skydips, focus and pointing etc.

Send comments to APEX Web Team

Last update : March 1, 2006