HartRAO single-dish observing proposals
HartRAO 26m telescope observing modes
The HartRAO 26m radio telescope is used for astronomical, astrometric and geodetic Very Long Baseline Interferometry (VLBI).
Proposals for Astronomical VLBI should be submitted to the radio telescope networks with which HartRAO participates. These are the European VLBI Network (EVN) and Australia Telescope Long Baseline Array (AT-LBA).
Astrometric and geodetic VLBI is usually carried out through the International VLBI Service for Astronomy and Astrometry (IVS).
In addition, the radio telescope is used for single-dish observing, which is described below.
HartRAO 26m telescope single-dish observing
For single-dish observing with the 26m telescope, multiple receivers are available. Their technical characteristics are summarised in HartRAO 26m Radio Telescope Details webpage.
Data from single-dish observing is controlled by the linux-based “New Control Computer System” (NCCS). This supports queue-scheduled, unattended observing.
Single-dish observing modes available with the 26m telescope are:
- Radiometry – Single-channel radiometers provide mesurements of signal intensity in two orthogonal polarizations, normally left- and right-hand circular. This is used for measuring the flux density of compact radio sources such as quasars, usually by means of drift scans in which the telescope is parked a little west of the object of interest and the signal is sampled as Earth rotation moves it through the telescope beam. The 5GHz/6cm and 8.4GHz/3.5cm receivers have dual-beam Dicke-switched receivers for cancelling atmospheric fluctuations. Other receivers can be operated in noise-adding gain stabilised mode to reduce the effect of gain variations in the receiver. Data extraction and reduction software is available for processing these scans (Michael Gaylard). Driven scans of user-defined length can be carried out, for example for mapping an area of the sky. “Basket-weaving” software is available for processing scans into a map (Sarah Buchner). For more information see the continuum radiometry” webpage.
- Pulsar timing – The old single channel pulsar timer is being replaced by a multi-channel FPGA-based IBOB board configured to cover a bandwidth of 400MHz. Data extraction and reduction software is available (Sarah Buchner). Industry standard TEMPO-2 pulsar software is used to process the data. For more information see Pulsar observing with the HartRAO 26m telescope.
- Spectroscopy – An autocorrelation spectrometer is available, providing up to 32MHz bandwidth across 1024 channels per polarization. Data extraction and reduction software is available (Michael Gaylard). For more information see Spectroscopy with the Hart 26m Telescope.
The queue-scheduled observing operates with user written input files. The format for these, and the key words used to specify the details of each observation (“scan”) is described in NCCS Input Files for Single-Dish Observing. However HartRAO staff will assist in creating observing input files.
Prospective observers are encouraged to discuss and refine their needs with the HartRAO Time Allocation Committee (firstname.lastname@example.org) before submitting a formal observing proposal.
The single-dish observing proposal form is available here. Please complete and email to the HartRAO Time Allocation Committee (email@example.com).
26m Telescope - Astronomical Very Long Baseline Interferometry (VLBI)
The Very Long Baseline Interferometry (VLBI) Technique
The radio telescope at Hartbeesthoek regularly operates as part of arrays of radio telescopes around the Earth and in space. When operating in this way, data are recorded simultaneously from each object at the same time at each telescope. The data streams from the telescopes are correlated later by computer. The interference pattern observed between the signals recorded at each pair of telescopes allows the brightness distribution of the radio source to be reconstructed and an image of it created. An example is shown below. The larger the “virtual telescope” created by this technique, i.e. the further apart the individual telescopes are, the finer the detail that can be seen in the radio source. Details with an angular size of one millionth of a degree can typically be seen.
In 2008 May, the first e-VLBI experiments were conducted in which the 26m telescope at Hartebeesthoek was linked directly to a correlator in Europe, together with telescopes on other continents, to produce real-time VLBI.
Astronomical VLBI observations at HartRAO
For astronomical VLBI HartRAO operates as part of a number of networks covering:
- Europe – the European VLBI Network – EVN
- Australia – the Australia Telescope – Long Baseline Array – AT-LBA
- Global Array – the EVN + US VLBA + others
- Space VLBI with orbiting radio telescope Radioastron and other ground-based radio telescopes.
- Astrometric and geodetic VLBI data may also be processed for information on changes in the structure of the quasars that are the targets in these experiments. The IVS Live website allows the progress of these experiments to be followed in real time.
Click on the image for a large version.
VLBI instrumentation at HartRAO
All the installed receivers on the 26m telescope at HartRAO are VLBI-capable, as is th econecentric SX band reciever on the 15m telescope. Local oscillator systems phase-locked to a hydrogen maser frequency standard – there are three available, providing backup. The MkIIIA VLBI recording terminal was upgraded to Mk5 standard. Two Digital Baseband Converters (DBBC’s) are in use, and data are recorded on disk packs in two Mark 5B+ recorders. The two telescopes can run VLBIs in parallel. A third Mark 5B+ is used for diskpack conditioning and e-shipment of VLBI data. There is a 10 Gb/s international network connection for real-time eVLBI and for e-shipment.
VLBI observations of Centaurus A
The giant elliptical galaxy NGC5128 in the southern constellation of Centaurus produces radio-emitting jets of hot gas. The galaxy is the brightest radio emitting object in the constellation, and hence is also known as “Centaurus A”. The jets are thought to emerge from around a black hole with a mass of some billion solar masses. The gravity of the black hole draws in nearby stars and gas, which provide the fuel for the jet. It provides an example of what can be observed with the VLBI technique. HartRAO has been involved in a number of VLBI experiments to look at the details of the structure of the jet, and changes in the structure over time.
Hartbeesthoek participated in the space VLBI programme with VSOP/HALCA, the Japanese radio telescope that orbited the Earth. Examples of the extremely high angular resolution obtained with a telescope in space that reaches altitudes of up to 21 000 km are shown at the VSOP Image Gallery. This mission has completed.
The Russian Radioastron orbiting radio telescope became operational in 2012. To obtain sufficient sensitivity it usually needs ground-based telescopes of 50m diameter or more, but the HartRAO 26m telescope has also participated in VLBI with Radioastron.
26m Telescope - Continuum Radiometry
Continuum Observing with the Hart 26m Telescope
Radio continuum emission is the broadband radiation emitted in the radio part of the spectrum by celestial objects. Its intensity (brightness temperature) typically varies relatively slowly as a function of wavelength (or frequency). This is in contrast to the narrow emission lines produced at characteristic frequencies by atoms and molecules. Continuum observations can be made with all installed receivers at HartRAO.
Point source flux measurements
For flux measurements of unresolved (“point”) sources, several observing methods are available:
- drift scans, with scans offset at the half-power points North and South if needed to check pointing accuracy
- crossed scans
- five-point stepping at the first nulls of the beam, the half-power points and on source, in the RA and DEC directions.
These enable pointing corrections to be determined where necessary (shorter wavelengths), so that the the on-source flux density can be corrected for pointing error.
An example of flux measurements made with the 6 cm / 5 GHz and 3.5 cm / 8.5 GHz dual-beam receivers is shown below.
- HartRAO single-dish observing proposals
- 26m Telescope – Astronomical Very Long Baseline Interferometry (VLBI)
- 26m Telescope – Continuum Radiometry
- 26m Telescope – Pulsar Timing
- 26m Telescope – Spectroscopy
- 26m Telescope – Webcam
- 26m Telescope – Control Computer System
- 26m Telescope – Technical details
- 26m Telescope – Surface upgrade 1998 – 2005
- 15m Telescope – built as eXperimental Development Model (XDM) for KAT
- 15m Telescope – Webcam
- 15m Telescope – Technical details
- HartRAO Local Sidereal Time clock
- The Square Kilometer Array (SKA) and the Karoo Array Telescope (KAT) Projects
- 7.5m C-BASS – C-band All Sky Survey Southern Telescope
- Practicals, projects and courses in Radio Astronomy for university students
Last Updated on December 13, 2022