Onsala 20 m telescope proposals

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

Due to the corona virus situation and its effect on observations, the spring Call for Proposals for observations with APEX (Swedish time), the Onsala 20 m telescope, and the Swedish LOFAR station (stand-alone mode) has been cancelled. The next Call for Proposals will be announced after the summer.


​Last Call for proposals (deadline 18 October 2019)

Proposals are invited for observations with the Onsala 20 m telescope in the period April – August 2020. We welcome proposals for Large programmes, i.e. spanning more than one semester and/or require a large number of hours (>~500 h)​.
Deadline: Friday 18 October 2019 (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.)​
Onsala Space Observatory, the Swedish National Facility for Radio Astronomy, is located about 45 km south of Göteborg, on the west coast of Sweden. The Onsala 20 m diameter millimetre-wave telescope is used for, e.g., observations of spectral line emission from molecules in comets, circumstellar envelopes, and the interstellar medium in the Galaxy and in extragalactic objects. (It is also used for astronomical and geodetic VLBI observations, through a separate proposal procedure.)
Our receivers provide continuou​s frequency coverage in the ranges 18-50, 67-87 and 85-116 GHz with 4 GHz IF bandpass, dual polarisations and full mutual sideband rejection (<−13 dB)If the spectrometer bandwidth is reduced to 2.5 GHz  then in the two high frequency bands both sidebands can be observed simultaneously ("2SB"), with these sidebands having centres 12 GHz apart. T​his spectrometer setup enables e.g. such important lines as CS 2-1 near 98 GHz, and 13CO/C18O near 110 GHz, to be observed at the same time. The lower portion of the 3/4 mm band, 67-87 GHz, became available in 2016 through the installation of a HEMT-based receiver which opens up observations of low-energy or ground state transitions of some important deuterated species such as DCO+, DCN, DNC, N2D+, HDO, DC3N etc.
The new control system, Bifrost, allows more automatised observations through advanced scripting. Large programmes can thus be observed mostly in service mode, but such proposals must have a dedicated local team member,  who can learn to understand the observing scripts and do data reduction. A trivial example of an automatised observation that can now be done is a large raster map being observed multiple times where the system autonomously decides which positions to observe based on their current (theoretical) noise levels, and at regular intervals temporarily retunes and conducts pointing/focus observations. Spectral scans including automatic retuning, and observations of a large number of sources at the same frequency, are also supported.

Observing period and operations:

This Call for proposals is for the observing period 1 April – 31 August 2020.

The telescope is open for scientists from all countries. Co-operation with Swedish scientists is encouraged (but proposals will be evaluated solely on scientific merit). Large programme proposals require a member of the proposing team to be at Chalmers to act as a local contact. 

Observers are welcome to visit Onsala to prepare and/or carry out their observations. Most aspects of an observation can be simulated beforehand using an off-line version of the control system. Observations may be carried out remotely using VNC interface depending on the type of project and the observers' previous experience.

Projects will be preferentially scheduled in 24 h blocks; multi-source proposals should consider this in making their source selection.


  • Radome-enclosed, 20 m diameter telescope, operated 24 h/day.
  • Location: Onsala, 45 km south of Göteborg, on the west coast of Sweden. Latitude 57° 23' 45.0046" N, longitude 11° 55' 34.8719" E, elevation 22.758 meters.

Receivers, spectrometers, etc.:

The telescope is equipped with receivers for the 18–50 GHz and 67–116 GHz ranges. Receiver characteristics:

Frequency range


​Receiver temperature

(single sideband)

​Receiver type




​18–26 GHz ​30 K ​HEMT amplifier ​Dual
​26–36 GHz ​50 K ​HEMT amplifier ​Single
​36–50 GHz ​50 K ​HEMT amplifier ​Dual
​67–87 GHz ("4 mm") ​50–60 K ​HEMT amplifier ​Dual
​85–116 GHz ("3 mm") ​45–60 K ​SIS mixer ​Dual

Note: Both the 3 mm and the 4 mm receivers are dual polarisation sideband separating with USB and LSB having centres presently 12 GHz apart. Each sideband has IF bandwidth 4 GHz, but  there is only sufficient spectrometer capacity to observe single sideband 4 GHz bandwidth or dual sideband 2.5 GHz. The IF bandwidth for the receivers for < 50 GHz is also 4 GHz ​but only one sideband can here be observed at a time (single-sideband).

Example spectra from the early commissioning observatations with the 3 mm and 4 mm receivers can be found here. Weak broad extragalactic lines can be detected down to a line strength of 2 mK or possibly better with the 3 mm recevier, and down to 4 mK or most likely better with the 4 mm receiver (TA*, after baseline subtraction).

Note that the atmospheric transmission decreases towards the low frequency end of the 4 mm band due to several broad atmospheric molecular oxygen lines around 60 GHz.


Science verification observations with the 4 mm receiver were performed during the first months of 2016. The observed projects can be found here

The back-ends for spectral line observations consist of three Fast Fourier Transform spectrometers (OSA, SPE, and HRF). The spectrometers have the following characteristics:
​Spectrometer Total bandwidth​ Resolution ​
HRF*​ 2 x 0.2, ..., 2 x 50 MHz​ ​24, ..., 6000 Hz​
SPE​** 2 x 100, 1 x 1000 MHz 12, 61 kHz​
OSA*** 2 x 4 GHz***, ​2 x 2.5 GHz, 2 x 625 MHz, 2 x 156 MHz 76, 76, 19, 4.8 kHz


* Please notify the telescope scientist as soon as possible after proposal submission if the HRF spectrometer is requested; there may be some lead time before it is available.​

**In dual polarisation and low resolution mode, the bandwidth is 500 MHz per polarisation.

***The two parts of the spectrometer can be connected either to two polarisations of the same sideband, or to the upper and lower sidebands. An additional mode, 4 x 2.5 GHz simultaneously covering all sidebands and polarisations, is available. Below 50 GHz, the 2 x 4 GHz mode can be used to cover both polarisations of the same sideband for the two dual polarisation receivers (18–26 GHz and 36–50 GHz).

Observing modes: 
Position switching, frequency switching, and (above 67 GHz) beam switching (11 arcmin).
Observing time estimates:
Please use the online observing time calculator for observing time estimates

Proposal prepar​ation 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 observation with Onsala telescopes, and clearly show preliminary results. Observing time estimates should be made using the on-line observing time calculator. If observations are for Ph.D. work, this should be stated.

Further information:


Published: Thu 02 Apr 2020.