APEX proposals

Proposals are invited for observations with the APEX telescope in 2023.

(For information about ​proposals for Directors Discretionary Time (DDT): see the general proposal pageCalls for proposals for APEX observations will from now on be issued only once per year, but the posibility to submit ​proposals for Directors Discretionary Time (DDT)​ at any time remains.​)

Deadline: Friday 17 February 2023​ (23:59:59 UTC)
If you are 
considering submitting close to the deadline, please note that support will only be available during normal office hours. Proposals are to be submitted through the NorthStar system.​

APEX, the Atacama Pathfinder EXperiment, is a 12 m diameter submillimetre telescope at 5100 m altitude on Llano Chajnantor in Chile. Starting in 2023, the APEX telescope is operated solely by Max-Planck-Institut für Radioastronomie (MPIfR). However, the Onsala Space Observatory continues to support APEX and in return PI:s with a Swedish affiliation have access to APEX observing time for 13 days in 2023 (see details below).​

Proposals for Swedish time on APEX must have a PI with a Swedish affiliation.

Note that Large Programm​e proposals are not invited.

The receivers offered in this Call are the heterodyne receivers SEPIA (SEPIA180: 159-211 GHz; SEPIA345: 272-376 GHz; SEPIA660: 578-738 GHz) and nFLASH (nFLASH230: 200-270 GHz; nFLASH460: 385-500 GHz).

On this page you will find information about:

  • Observing period, operations, etc.
  • Telescope
  • Receivers
  • Proposal preparation and submission
  • Further information and useful links

Observing period, operations, etc.:

This Call for proposals is for Swedish time on APEX in 2023​. There will be three observation blocks:

  1. May 10-12 (3 days)
  2. early July (5 days)
  3. late October (5 days) 

>>> Important: Please indicate the block(s) when your sources can be observed. The following 16 h LST intervals are available in the blocks:

  1. LST 09-01 (the first part, LST 09-14, is occupied by Concerto observations each day)
  2. LST 14-06
  3. LST 20-12

These LST intervals correspond to the Chilean night time and early morning time when the weather is expected to be best. Observations of sources closer than 30 degrees from the Sun are not allowed.

Observations will be performed in service mode.


  • 12 m diameter telescope for mm and sub-mm waves.
  • Location: Llano de Chajnantor, 50 km east of San Pedro de Atacama, northern Chile. Latitude: 23º00'20.8" South, longitude: 67º45'33.0" West. Elevation: 5107 m.


***  SEPIA (ALMA bands 5, 7 and 9)  ***
The SEPIA instrument is designed to house three ALMA-style receiver cartridges, covering ALMA bands 5, 7 and 9. All three receivers are dual-polarization sideband-separating (2SB):
- SEPIA180 (ALMA band 5): 159–211 GHz.
- SEPIA345 (ALMA band 7): 272–376 GHz.
- SEPIA660 (ALMA band 9): 578–738 GHz.

Spectrometer: The SEPIA receivers use a Fast Fourier Transform Spectrometer with an IF bandwidth of 4 GHz (band 5) or 8 GHz (band 7 and 9; 7.85 GHz in practice). The spectrometer covers 4 or 8 GHz for each polarisation and for each sideband (i.e., 4x4 or 4x8 GHz in total). There is a gap of 8 GHz between the two sidebands. The channel separation is 61 kHz.
The offered observing patterns are on-off observations, raster maps, and on-the-fly (OTF) mapping. The data will be taken in either beam-switching or position switching mode.
Please use the online observing time calculator at the APEX web site for observing time estimates. The instrument setup tool is very useful when planning spectral line observations.

Technical details for the band 5 receiver can be found in the following publication: Billade, B., et al. “Performance of the First ALMA Band 5 Production Cartridge”, IEEE Trans. Terahertz Science and Technology, Vol. 2, No. 2, March 2012, pp. 208-214. For a technical description of the band 9 receiver, please see the following publication: Baryshev, A. M., et al. "The ALMA Band 9 receiver. Design, construction, characterization and first light", Astronomy & Astrophysics, Vol 577, A12 (February 2015).

***  nFLASH (ALMA bands 6 and 8)  ***
nFLASH is a facility instrument containing two receivers, covering (roughly) ALMA bands 6 and 8. Both receivers are dual-polarization sideband-separating (2SB). The dual-colour operation (using the 230 GHz receiver simultaneously with the 460 GHz receiver) is an option.
- nFLASH230 (ALMA band 6): 200–270 GHz.
- nFLASH460 (ALMA band 8): 385–500 GHz.
nFLASH230 has an IF bandwidth coverage of 8 GHz with a gap of 8 GHz between the two sidebands. nFLASH460 has an IF bandwidth coverage of 4 GHz per sideband. 
The spectrometer is the same as for SEPIA (see above). 
The offered observing patterns are on-off observations, raster maps, and on-the-fly (OTF) mapping. The data will be taken in either beam-switching or position switching mode.​
Please use the online observing time calculator at the APEX web site for observing time estimates. The instrument setup tool is very useful when planning spectral line observations.

Atmospheric transmission:

It is important to consider the atmospheric transmission at the APEX site. The APEX web site provides information on the weather, including atmospheric transmission.

Proposal preparation and submission:

Onsala Space Observatory uses the NorthStar system for preparation and submission of proposals. NorthStar is used by several radio and optical observatories.

In NorthStar, information about applicants, instruments, targets, etc., is to be provided "on-line", and the scientific justification is to be prepared "off-line" and uploaded as a pdf file (also target lists can be uploaded). NorthStar then produces one pdf file with all information. NorthStar includes information on how to use it.

The proposal must contain a proper and concise scientific justification including an explanation for how the requested observing time was calculated, in total no more than two A4 pages long, plus figures and tables if needed (for a total of maximum six pages). Proposers should mention relevant previous observations with Onsala telescopes, and clearly show preliminary results. Observing time estimates should be made using on-line observing time calculators. If observations are for Ph.D. work, this should be stated.

In order to avoid duplicating observations, please check the ESO archive for previous observations.

Further information and useful links:


Page manager Published: Fri 20 Jan 2023.