APEX proposals

(For information about ​proposals for Directors Discretionary Time (DDT): see the general proposal page.)

Proposals are invited for observations with the APEX telescope in the period July – December 2021.

Deadline: Thursday 6 May 2021 (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. The telescope is operated by Onsala Space Observatory, Max-Planck-Institut für Radioastronomie (MPIfR), and European Southern Observatory (ESO).

Note that Large Programme proposals (see below) are invited.

The receivers offered in this Call are:

  • the heterodyne receivers:
    • SEPIA (SEPIA180: 159-211 GHz; SEPIA345: 272-376 GHz; SEPIA660: 578-738 GHz)
    • nFLASH (nFLASH230: 200-270 GHz; nFLASH460: 385-500 GHz)
  • the bolometer array:
    • ArTeMiS (350 and 450 μm).

The Swedish share of the APEX collaboration is (from 2018) 13%. In general, proposals for Swedish time on APEX must have a PI or at least co-I with Swedish affiliation, but see below for exceptions.

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 the period July – December 2021 (the Swedish observations are planned for July and September, see the APEX Science schedule).

In general, proposals for Swedish time on APEX must have at least one co-I with a Swedish affiliation; however a maximum of 20% of the observing time will be open to international proposals (i.e. those without a PI or co-I with a Swedish affiliation) - to be scheduled based purely on scientific merit.

Observations on Swedish time on APEX are supported by the Transnational Access programme of the OPTICON RadioNet Pilot (ORP) project funded by the European Commission (grant agreement number 101004719). Observers might be asked to provide information requested by the EC.

Note that the weather is best during night time and early mornings, which is important to consider for observations at the higher frequencies. 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.


SEPIA660 is an APEX facility instrument, available for all users. SEPIA345, nFLASH230 and nFLASH460 are not yet accepted as facility instruments but are made available for science observations for all users. ArTeMiS and SEPIA180 are partner instruments which will be fully available on Swedish time for all users
There are protected guaranteed time observations for some instruments (see ESO Guaranteed Time Observations for Period 108), in particular several sources for the ArTeMiS consortium.
***  ArTeMiS  ***
ArTeMiS is a bolometer array working simultaneously at 350 and 450 μm, developed by CEA Saclay (France). At 350 μm, the field of view is 4.7' x 2.3' and the number of pixels is 2304. Please use the online observing time calculator at the APEX web site for observing time estimates. 

***  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 new facility instrument, offered depending on a successful commissioning. It contains two receivers, covering (roughly) ALMA bands 6 and 8. Both receivers are dual-polarization sideband-separating (2SB), and can be used simultaneously:
- 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.

Proposals for Large Programmes:

Up to a maximum of 30 % of the observing time distributed by the programme committee can be allocated to Large Programmes. The definition of a Large Programme is as follows:
  • a programme requiring a minimum of 100 hours of APEX telescope time, spread until the end of 2022;
  • a programme that has the potential to lead to a major advance or breakthrough in the field of study, has a strong scientific justification, and a plan for a quick and comprehensive effort of data reduction and analysis by a dedicated team.
A good organizational structure of the proposing team, availability of resources, relevant expertise and computational facilities must be demonstrated in the proposal. Because of these extra requirements, the proposer may use six pages (instead of two for normal proposals), plus figures and tables. PIs of successful proposals for Large Programmes are required to provide all data products (processed images and spectra, catalogues) to the ESO archive by the time of the publication of their scientific results in a refereed publication.

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.

Please also check the ESO Guaranteed Time Observations for Period 108, in order to avoid conflicts.

Further information and useful links:

  • The NorthStar proposal submission tool.
  • If observing time for the project is also requested from another APEX partner (ESO or MPIfR, or Chilean time), this must be stated in the proposal.
  • Source coordinates (RA, DEC) must be given in J2000.
  • Give the required weather conditions in terms of PWV (precipitable water vapour).
  • Give the ESO User Portal username of the P.I. (needed for archiving data), see ESO User Portal​.
  • For further technical information, see the (new) APEX web site​.
  • Please use the observing time calculators​ available on the APEX web site.
  • The instrument setup tool is very useful when planning spectral line observations.
  • The APEX science schedule​.
  • Observers granted time on the telescope will be asked to prepare the observations by filling in a project submission form on the APEX web site.
  • Questions about the telescope, receivers, observations, etc.: per.bergman@chalmers.se.
  • In case of problems with NorthStar: michael.olberg@chalmers.se.
  • General questions about proposals: magnus.thomasson@chalmers.se.

Page manager Published: Tue 30 Mar 2021.