Onsala 20 m telescope proposals

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

From 2020 onwards, there will be only one Call for proposals per year for the Onsala 20 m telescope, in the autumn, but the posibility to submit ​proposals for Directors Discretionary Time (DDT)​ at any time remains.

**** Latest Call for proposals for the 20 m telescope ****

Proposals are invited for observations with the Onsala 20 m telescope in the period January–April 2021. We welcome proposals for Large programmes, i.e. spanning more than one semester and/or require a large number of hours (>~500 h)​.

Deadline: Wednesday 18 November 2020 (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 for the 20 m telescope must have at least one co-I with a Chalmers affiliation. Calls for proposals for the 20 m telescope 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.
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, enables ​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. 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 January–April 2021.

From now on, there will be only one Call for proposals per year (for the Onsala 20 m telescope), but the posibility to submit ​proposals for Directors Discretionary Time (DDT)​ at any time remains.

Note: Proposals for the Onsala 20 m telescope must have at least one co-I with a Chalmers affiliation.​

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 if both linear polarisation products are to be recorded. 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 four modules of the spectrometer can either be combined to cover 4 GHz in both polarisations in the same sideband, or to cover the upper and lower sidebands in one polarisation. 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:



Page manager Published: Thu 01 Apr 2021.