Onsala 20 m telescope proposals

​Call for proposals

Proposals are invited for observations with the Onsala 20 m telescope in the period September 2017 – March 2018.
Deadline: Friday 5 May 2017 (23:59:59 UTC)
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.)
A new receiver for the 67–87 GHz range ("4 mm"), with a receiver temperature of approximately 50–60 K, was installed in October 2015. The 4 mm band is available to European astronomers only on very few telescopes. The band around 4 mm contains a rich collection of molecular-line transitions, including those of many deuterated species: DCO+, DCN, DNC, N2D+, DC3N, HDO, C3HD, etc. Many of these lines have never been observed extensively, and it should be stressed that the low temperatures of interstellar clouds make the lowest-lying transition particularly observationally important. Measuring the ratios of normal and deuterated species provides a sensitive test of various proposed chemical pathways within molecular clouds.
A new spectrometer (FFTS) with 2 x 4 GHz bandwidth was installed in December 2015. An additional new mode, 4 x 2.5 GHz, is also available.

Observing period and operations:

This Call for proposals is for the observing period 1 September 2017 – 31 March 2018.

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).

Observers are expected to visit Onsala to carry out their observations.

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)

​30 K

​Receiver type




​18–26 GHz ​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: The 3 mm receiver was installed in March 2014, and the 4 mm receiver in October 2015. 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. The IF bandwidth for the receivers for < 50 GHz is about 4 GHz (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 witht 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 one hybrid digital autocorrelation spectrometer (HRC) and two Fast Fourier Transform spectrometers (SPE and OSA). The spectrometers have the following characteristics:
​Spectrometer Total bandwidth​ Resolution ​
HRC*​ 0.05, ..., 6.4, 12.8 MHz​ ​0.03, ..., 4, 8 kHz​
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


* The HRC may soon be replaced by a software spetcrometer with similar capacity. Please contact the telescope scientist for more information.

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

***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 polarizations of the same sideband for the two dual polarization 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 preparation and submission: 

Onsala Space Observatory uses the NorthStar system for preparation and submission of both 20 m telescope and APEX 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: Fri 15 Aug 2014. Modified: Mon 20 Mar 2017