This section describes relevant changes for observations to take place during Period 105.

General

APEX upgrade:

The upgrade of the APEX telescope was completed in April 2018. It consisted of:

• the replacement of the M1 surface panels with panels of higher accuracy, optimizing the telescope efficiency for high frequencies;
• the replacement of the entire secondary unit with a new wobbler, allowing to switch between on and off positions separated by up to 10' at a rate of up to 2 Hz;
• new telescope drives;
• a new shutter mechanism.

In parallel, a new set of facility instruments is being installed (SEPIA and nFLASH), which replace the decommissioned SHFI.

Dates for ESO observing time:

The dates for the ESO observing time in Period 105 are expected to be in late March, May and July 2020. Time critical observations should only be requested within these time slots. Users are encouraged to check the latest version of the schedule.

ESO share in the APEX collaboration:

The ESO share in the APEX collaboration has increased from 27% to 32%. The exact distribution of the observing time between the APEX partners can be found on the APEX web pages.

Length of normal programmes:

In order to solicit longer normal programmes for observations that do not require the best weather conditions, the maximum length of normal programmes on the instrument PI230 has been raised to 199 hours. For any other instrument, the limit remains 99 hours. Any PI230 programmes requiring 200 hours or more should also be requested as Large Programmes.

Monitoring programmes:

Monitoring programmes will only be accepted for ARTEMIS and SEPIA (SEPIA-180 and SEPIA-660).

Instruments

• ARTEMIS: in Period 105, both the 350 and 450 μm channels are offered for simultaneous observations. This instrument is optimized for wide-field mapping of areas of at least 4'x2', and achieves similar mapping speeds at both wavelengths. An observing time calculator is available.
  
• LABOCA: The 870µm bolometer array is offered in Period 105 depending on a sufficient demand and a successful completion of the re-commissioning activities in the Cassegrain cabin. No Large nor Monitoring Programme proposals will be accepted for LABOCA, as its capabilities are expected to be superseded by a new bolometer array that has a wider eld-of-view, namely, A-MKIDs.
• nFLASH: This new Facility Instrument is offered depending on a succesful commissioning in Q1 2020. It will contain two receivers replacing the PI230 and FLASH receivers: nFLASH230, covering from 200 to 270 GHz, and nFLASH460, covering from 385 to 500 GHz. Both are dual polarization 2SB receivers, and can be used simultaneously. The nFLASH230 receiver has an IF bandwidth coverage of 8 GHz with a gap of 8 GHz between the two sidebands; the nFLASH460 receiver has a IF bandwidth coverage of 4 GHz per sideband. The backends are digital 4th generation Fourier Transform Spectrometers (dFFTS4G) with 24 GHz bandwidth. An observing time calculator is available. In case of delays in the commissionig proposal may be executed with the PI230 and FLASH receivers instead (the latter only in collaboration with the instrument team).
  
• PI230: This 230 GHz receiver is no longer offered in P105.
  
• SEPIA can house
  
  • 3 ALMA-type receiver cartridges with dual polarization, sideband-separating mixers (2SB)
    
    • SEPIA-180 (ALMA band 5) receiver, covering 159 to 211 GHz,
      
    • a new SEPIA-345 (ALMA band 7) receiver, covering 272 to 376 GHz,
      
    • SEPIA-660 (ALMA band 9) receiver, covering 578 to 738 GHz; note the extended frequency coverage with respect to the ALMA band 9 receivers.
      
  • Only the SEPIA-180 and SEPIA-660 receivers are available for Monitoring and Large Programmes.
  • The SEPIA-345 receiver is offered conditional to a successful commissioning in July 2019; any observations in this band will be executed with FLASH-345 instead if SEPIA345 is not available.
    
  • All receivers use the XFFTS backends, covering 4 GHz IF bandwidth coverage with a gap of 8 GHz between the image and the signal bands. For SEPIA-345 and SEPIA-660, this may be upgraded to 8 GHz bandwidth per IF and polarization with the expected commissioning of the new Facility FFTS4G.
  • An observing time calculator for all bands is available.
• CHAMP+: This MPIfR PI instrument is not offered since Period 101 due to ongoing re-commissioning activities.