Ooty Radio Telescope (ORT)
The Ooty Radio Telescope
About ORT:
The large radio telescope near Ootacamund (Ooty) was set up by TIFR radio astronomers, in the picturesque Nilgiri Hills of South India in 1970. Designed and built in India, the Ooty Radio Telescope (ORT) is an off-axis parabolic cylinder 530 m long and 30 m wide operating at a nominal frequency of 326.5 MHz with a maximum bandwidth of 15 MHz at the front-end. The reflecting surface of the telescope is made of 1100 thin stainless-steel wires running parallel to each other for the entire length of the cylinder and supported on 24 steerable parabolic frames. An array of 1056 half-wave dipoles in front of a 90 degrees corner reflector forms the primary feed of the telescope.The unique feature of the design is that the telescope has been constructed on a hill which has a natural slope of about 11 degrees, the same as the geographical latitude of Ooty. This makes the long axis of the telescope parallel to the Earth's rotation axis, giving it an equatorial mount. A celestial source in the sky can be tracked for about ten hours at a stretch by mechanical rotation of the parabolic cylinder in the east-west direction. In the north-south direction, the telescope response is steered electronically by introducing a suitable phase and delay gradient. along the dipole array.
The Ooty Radio Telescope came into operation in 1970 and has been in almost continuous use since then. Over the 25 years of its existence, it has produced many important astronomical results on radio galaxies, quasars, supernovae, pulsars, the interstellar and interplanetary media etc. One of the most successful observational programmes carried out for many years at Ooty was to determine the angular structures of hundreds of distant radio galaxies and quasars by the technique of lunar occultations. The application of this unique database to observational cosmology provided independent evidence against the Steady-State theory of Universe and supported the Big-Bang model of the Universe. The telescope is currently being used mainly for the study of pulsars, radio recombination lines and interplanetary scintillations.
Upgradation of ORT:
The front-end reciever system of the ORT was upgraded with a low noise amplifier (Tamp = 50 K) and a strip line diode-switch controlled phase shifter following each of the 1056 dipoles. This upgradation improved the sensitivity of the system by a factor of two. Additionally the declination-setting and monitoring system was computerized leading to enhanced stability. A new local oscillator phase shifter with increased accuracy has improved the response of ORT over the entire 15 MHz bandwidth and also increased the declination range visible to the ORT. The present system supports electronic steering to declinations between -60 and +60 degrees.
The Receiver:
An array of 1056 half-wave dipoles in front of a 90 degrees corner reflector forms the primary feed of the telescope. The signals recieved by groups of 48 dipoles are added in-phase to form 22 group outputs, each known as a module . The northern modules are designated as N1 to N11 and southern modules as S1 to S11. The signal from each module are down-converted to an IF of ~30 MHz with a bandwidth of 15 MHz at the front-end. The LO signal for the downconversion is transmitted to all the modules over equal-length cables from a common source in the receiver room. The beam width due to each module is 2.3 degs in EW and 2.2 degs secant of declination (sec(dec)) in the NS. The outputs from the 22 modules of the ORT are brought to the receiver room for further processing. The 11 north signals and 11 south signals are separately combined in a beam-forming network with proper delay compensations. This compensation for different geometric path lengths between the different modules generates 12 beams for each half of the ORT. The telescope can be operated in either total power or correlation mode. In the total power mode, the 12 beams each from north and south are added to generate a beam with width of 2.3 degs in EW and 5.5' sec(dec) in the NS. In the correlation mode, the beams from the north and the south are multiplied to generate the correlation beams with a width of 2.3 degs in the EW and 3.3' sec(dec) in the NS. The adjacent beams are separated by 3'sec(dec) . The twelve beams are called Beam 1 (southern most beam) to Beam 12.
Backends:
- Analog Correlator: Used for IPS observations.
- Spectral Line Receiver and 512-channel Autocorrelator:
The spectral line receiver was specially designed for radio recombination
line observations in the ORT band. The 15-MHz band contains four
electronic transitions near n = 271 . The receiver has been
designed to downconvert the 15 MHz band near 30 MHz to four basebands of
width ~1 MHz centered at desired line frequencies.
Four fixed local oscillators are employed to achieve this.
The four baseband outputs are then fed to the one-bit 512-channel
autocorrelator which is actually used as a 64-channel spectrometer
so as to process 8 signals simultaneously. A recirculator has been
built for temporary storage and recirculation of data through the
autocorrelator. In the existing system, the data are recirculated
12 times through the 64-channel correlator to achieve the desired
resolution of ~ 1 kHz over a band of 760 kHz.
Using this system, radio recombination lines have been observed from
the entire Galactic plane accessible to the ORT.
The receiver and autocorrelator can also be used in another mode of operation to observe pulsars and 21-cm lines.
- Pulsar machine: ?
Ongoing Projects:
- IPS observations.
- Pulsar Timing observations.
More information on the ORT system can be found in:
- Swarup, G., et al, 1971, Nature Physical Sciences, 230, 185.
- Selvanayagam, A.J., Praveenkumar, A., Nandagopal, D., Velusamy, T., 1993, 1ETE Technical Review, 10, No. 4, 333.
- Roshi, A.D., 1995, MSc Thesis, Poona University.
- Subrahmanyan, R., 1989, PhD Thesis, Indian Institute of Science, Bangalore.
How to apply for time on ORT: Write a brief scientific proposal outlining your experiment and the telescope time required for it. Remember that you will have to travel to Ooty to conduct your observations - remote observing is not an option available. Send your observing proposal to Dr. P.K.Manoharan at the RAC address given below.
How to reach RAC from Pune:
Reach Bangalore by air/rail/road.
Catch a bus to Ooty Central bus station from Bangalore.
From there board a bus going towards Kallakorai/Palada/Ithalar/
Nanjnad/Emerald and alight at Muthorai village. RAC is about
1 km away from Muthorai. A pleasant uphill walk.
Telephone : (91-423) 2550334, 2550335 2550665 (Direct)
Last Revised: November 2002
Address:
Radio Astronomy Centre
Tata Institute of Fundamental Research
Post Bag 8, Ooty - 643001, Tamil Nadu, INDIA
FAX : (91-423) 2550135
Contact: www@ncra.tifr
.res.in