2004 ASTRONOMY & ASTROPHYSICS - Indian Academy of Sciences

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CHAPTER 5 three telescopes, operating at 103 MHz, at Thaltej (near Ahmedabad), Rajkot and Surat, to study interplanetary scintillations of radio sources. Unfortunately, this telescope was dismantled a few years ago because of severe interference from FM broadcasts. Millimetre wave astronomy A 10 m diameter antenna of high mechanical accuracy (~ 200 micron rms ) was constructed by the National Aerospace Laboratory, Bangalore in collaboration with the scientists and engineers at the Raman Research Institute. The sophisticated receiver systems for this telescope was developed at the Radio Astronomy Laboratory at RRI by N.V.G. Sarma and his team. This telescope was installed in 1985 at the Raman Research Institute Telescope, of 30,000 square metres effective area, in the mid 1980s. This telescope, built by TIFR, became operational by 1999 at Khodad, about 80 km north of Pune. It consists of 30 fully steerable parabolic dish antennas of 45 m diameter, spread over an area of 25 km in diameter. What is remarkable about these antennae is their modest cost inspite of their giant size. This has become possible, thanks to a significant new technological breakthrough achieved by Indian scientists and engineers. This concept nicknamed SMART (for Stretched Mesh Attached to Rope Trusses), has enabled the dish to be light-weight and of low solidity by replacing the conventional back-up structure by a series of rope trusses (made of thin stainless steel wire ropes) stretched between 16 parabolic frames made of tubular steel. The telescope has five operating frequency bands around 150 MHz, 233 MHz, 325 MHz, 610 MHz and 1000–1450 MHz. A limited number of antennae operate in an additional higher frequency band to allow observations of the OH molecular transition. The 10.4 m millimeter telescope at the Raman Research Institute and was used to study carbon monoxide in nearby molecular clouds, silicon monoxide maser emission from the outer envelopes of red giant stars, and cometary globules. Currently, this telescope is being used only at centimetre wavelengths. The Giant Metrewave Radio Telescope (GMRT ) As we enter the new century, the major facility for radio astronomy in India is the GMRT. The Ooty group proposed the Giant Metrewave Radio The GMRT is a modern, state-of-the-art, aperture synthesis radio telescope. The antenna configuration is a hybrid one, with 14 antennae packed into a compact array about 1 km × 1 km in size and the remaining 16 antennae stretched out along three arms (called the “Y” arms), each 14 km long. The central compact array gives sensitivity for detecting diffuse emission, while the arm antennae provide high angular resolution. The telescope is thus very versatile, and at metre wavelengths it is the most sensitive aperture synthesis telescope in the world. Each antenna is connected to the Central Electronics Building by two wide-band optical fibre links. The entire array can be controlled from the CEB. There is also a high speed link between the 63
RADIO ASTRONOMY Central Electronic Building and the NCRA headquarters in Pune. This allows for remote operation of the telescope, as well as real time monitoring of the data quality. The backend of the GMRT is a 256 channel, 32 MHz bandwidth digital correlator. This sophisticated correlator system was developed by the scientists and engineers of the National Centre for Radio Astrophysics of TIFR. The 21 cm prime focus electronics, and also a major part of the Pulsar receiver, was built at the Raman Research Institute. In January 2002, GMRT was thrown open to the international astronomical community. During the past seven cycles of observations, a National Time Allotment Committee has approved more than 350 proposals for observation with the GMRT. It should be mentioned that a substantial fraction of these proposals (nearly a third) are from investigators abroad. These proposals cover a very wide range of topics: • The Sun • Pulsars • Supernova Remnants • Micro-quasars • The interstellar medium • Star forming galaxies • Gamma ray bursts • Extragalactic supernovae • Clusters of galaxies • Active galaxies • The intergalactic medium, etc. Many interesting results have already been obtained, many more can be expected in the coming years. The GMRT is now gaining recognition as a major international facility. Areas of Current Research In the past thirty years or so, the radio astronomers in the country have pursued their research programmes using the telescopes available in India, as well as other major international facilities like the Very Large Array in the U.S.A., the Australia Telescope, the Westerbork Synthesis Radio Telescope in the Netherlands, etc. With the commissioning of a versatile instrument like the GMRT radio astronomy has got a new impetus and one can hope to address many problems. The partial list given below should give an indication of the range of problems being pursued by Indian astronomers. • The Heliosphere Radio emission from the active regions on the Sun. Solar bursts, flares and coronal mass ejections. Dynamics of the solar wind. • Solar system objects Radio emission from Jupiter: coordinated radio, optical and X-ray observations. • Stars Flaring and quiet radio emission from cool dwarf stars. Radio observation of X-ray binaries. Massive young stellar objects. High angular resolution observations of Galactic star forming regions. Molecular transitions in star forming regions. • Micro-Quasars Radio observations of X-ray transients. Compact jets, and the disk-jet connection in micro-quasars. • Pulsars Emission geometry of pulsars. Multi-frequency studies of single pulses from pulsars. Scatter broadening of pulsars. Pulse arrival time observations. Search for pulsars in globular clusters. • Interstellar medium of the Galaxy The kinematics of interstellar clouds. Recombination radiation from the interstellar gas. Supernova remnants. Organic molecules in the ISM. • Galaxies Dynamics of normal and dwarf galaxies. 64
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ASTRONOMY & ASTROPHYSICS A Decadal
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This publication of the Academy on
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Preface The Indian Academy of Scien
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The Academy Committee for Astronomy
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h e P a n e l s Theoretical Astroph
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C H A P T E R 1 Executive Summary
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EXECUTIVE SUMMARY The recommendatio
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EXECUTIVE SUMMARY feasibility study
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C H A P T E R 2 The Present Revolut
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THE PRESENT REVOLUTION IN ASTRONOMY
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THE PRESENT REVOLUTION IN ASTRONOMY
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RECOMMENDATIONS was installed there
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RECOMMENDATIONS Keeping in mind the
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RECOMMENDATIONS The 1 m telescope a
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RECOMMENDATIONS as the technology t
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RECOMMENDATIONS The committee appre
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RECOMMENDATIONS • All Sky Monitor
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RECOMMENDATIONS using our facilitie
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RECOMMENDATIONS • The committee s
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List of addresses Radio Observatori
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S.N. Bose National Centre for Basic
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Indian Academy of Sciences C. V. Ra
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2004 ASTRONOMY & ASTROPHYSICS - Indian Academy of Sciences

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