A stellar acquisition

Published : Sep 29, 2001 00:00 IST

The Himalayan Chandra Telescope at Hanle, which was dedicated to the nation recently, promises to boost research in astrophysics and related areas.

IT is the closest that India can get to possessing a space telescope, at least for the present. Its recent acquisition, the Rs.39-crore 'Himalayan Chandra Telescope', is a land-based instrument, but the telescope's location, at 4,517 metres above mean sea level in the high-altitude desert of Hanle in Ladakh, affords it almost all the advantages of a space telescope. While the size of the telescope, which has an aperture measuring two metres, is not a matter of pride (there are quite a few telescopes of this size in the world), its location is - it has aroused the curiosity of many an astronomer in the world. Interestingly, the telescope, situated atop Mt. Saraswati, in the Digpa Rasta Ri range in the Nilankul plain, is remote-controlled through satellite from a location hundreds of kilometres away. The telescope, named after the Himalayas and the Indian-born Nobel laureate, Prof. S. Chandrasekhar, was dedicated to the nation on August 29.

Hanle's altitude, dry environment and sparse population make it an ideal place for locating a telescope. The low level of water vapour in the environment makes the nights more photometric (cloudless) and the high altitude ensures that the starlight is not scattered. Owing to the absence of any significant human habitation, the quality of starlight is largely unaffected by artificial light or any pollution.

At Hanle, the annual precipitation of rain and snow is less than 10 cm and the precipitable water vapour in the atmosphere is less than 2 mm. Satellite data showed that Hanle was the best observing window for a study of celestial objects in the infra-red, sub-millimetre and millimetre regions of the electromagnetic spectrum, which are normally beyond the reach of astronomical observatories at lower altitudes.

Hanle's high altitude will allow the telescope to penetrate above the denser strata of the atmosphere, which are closer to sea levels. Galactic objects can be viewed better from such rarefied altitudes, where the level of turbidity is low and, consequently, the extent of absorption and obscuration of light is comparatively less. At Hanle, the atmospheric pressure is around 580 millibars, which is 58 per cent of the pressure at sea level. As Hanle does not have a commercial electric line, there is no possibility of artificial light interfering with the quality of the starlight. Meteorological data have shown that the number of nights when astronomical spectroscopy can be done at Hanle is around 260, and the number of photometric nights is about 190.

Besides these advantages, the facilities available at the 256 ha Indian Astronomical Observatory at Hanle - located at longitude 78 57' East and latitude 32 47' North - are unique at least for half of the globe, between eastern Australia (157 East) and Spain's Canary islands (20 West). Thus, the observatory fulfils the long-felt need for an astronomical facility in this region.

According to Professor Ramanath Cowsik, Director, Indian Institute of Astrophysics (IIA), Bangalore and one of the key persons involved in the telescope project, Hanle has turned out to be one of the best sites in the world to locate an optical telescope and is as good as Mauna Kea in Hawaii, which is 4,200 m above sea level. "The telescope will be used as a space telescope and the possibilities are tremendous. With this telescope and that site, we have acquired 10 to 15 times the observing power (from telescopes) that we have so far had in this country," he said.

According to astronomers, Hanle is likely to face international competition only from Chajuantar (4,800 m above sea level) in Chile. Astronomers such as Peter A. Wehinger of the Steward Observatory in the United States say that India can develop other sites that are comparable to Hanle. Said Wehinger: "Ladakh has many sites; for example, Khardungla, north of Leh, where the water vapour is very low."

The Himalayan Chandra Telescope is remote-controlled through Insat 3B from the Centre for Research and Education in Science and Technology (CREST) at Hosakote, 30 km from Bangalore. This means that astronomers who want to use the telescope need not go to Hanle, where the temperature dips to -30C in winter.

Communication links have been established between Hanle and CREST in order to download observational and meteorological data and to perform remote-controlled operations of the dome and the telescope. Also, an integrated control system involving the telescope, the dome and the weather and cloud monitor has been evolved. It is supported by a video-conferencing facility between Hanle and Hosakote. Data received in the course of observations are archived.

According to Cowsik, the afterglow of a gamma ray burst is one of the key observations made by using the telescope so far. "This is one of the most energetic phenomena that can be seen. 1052 ergs of energy is radiated by the gamma rays in seconds. After the event we were able to observe a faint afterglow. Through this we can find out the astrophysics of how the gamma ray burst occurred."

The need for such a telescope was felt when the 2.34 m telescope at the Vainu Bappu Observatory at Kavalur in the Javadi hills of Tamil Nadu, which is operated as a national facility for optical astronomy, could not meet the increasing demand for observation time. Moreover, hostile weather conditions and bad skies often hampered observation at Kavalur. Also, there had been a growing demand for larger telescopes and new technology instrumentation.

Besides these problems, there is the fundamental limitation of the earth's atmosphere itself, which allows only a small window in the electromagnetic spectrum through which a ground-based astronomer can observe celestial objects. A series of meetings of astronomers and eminent scientists were held in 1989 under the auspices of the Planning Commission to find a way out of these problems. It was decided that a modern astronomical telescope should be set up at a suitable site for optical and infra-red observations. The new telescope should also be able to complement the observations carried out by other national facilities such as the Giant Metre wave Radio Telescope near Pune and the high energy gamma ray telescopes and X-ray telescopes that are aboard Indian satellites.

The IIA was entrusted with the task of setting up such a facility in 1992. The search for a proper site began. Said Prof. V. K. Gaur, Distinguished Professor, IIA; "The telescope had to be like a bun sitting on a big plate and the plate itself being perched on a high elevation."

The IIA chose Hanle, which it originally selected for its Himalayan Infra-red Optical Telescope (HIROT) project. Work started in 1997, when the site was approved as a national facility. In 2000, this new technology telescope, fabricated, installed and commissioned by the Electro Optic Systems Pvt. Ltd., of Australia, had the first rays of light pass through it. The telescope has a modified Ritchey-Chretien system where the primary mirror is a meniscus mirror made of ULE ceramic, which is designed to withstand the extreme weather conditions at Hanle. The telescope itself was made by the Australian company in the U.S. where the costs are comparatively low. The dome was constructed by Mengi Engineering Company, Jammu; and the liquid nitrogen plant, which is used to produce liquid nitrogen that helps cool the detectors and eliminate thermal electrons, was manufactured by Sterling Cryogenix of Denmark.

Dr. T.P. Prabhu, Project Manager, said: "The process of putting up a telescope at Hanle instilled a lot of confidence in the IIA staff. We were able to overcome big challenges. It took more than a year to assemble the Kavalur telescope but we took just three weeks to assemble the two-metre telescope at Hanle."

Prof. Yash Pal, chairman of the project management board, said: "It was a challenging task and it has been done. Lots of things have to happen now. Our astronomers should try and do (observe) new things (images) since they can now observe for a much longer period. We have to do first-rate astronomy; not just follow what others are doing."

Given its high cost, questions have been raised about the decision to go in for a "large" two-metre telescope. Cowsik said that in the first place a two-metre telescope was not large enough, though it was not too small either. "We may be able to afford only a 10-cm telescope, but there has to be a threshold point (for the size of the telescope), below which it is just not feasible to run a research establishment. It is a question of what we can afford in terms of time and money."

On the criticism as to why India had to go in for an imported telescope, eminent scientist Prof. B.V. Sreekantan said that India was still backward technologically. "We have neglected the field of material science, so we don't produce crucial materials," he said. He was all praise for India's strides in space technology which, he pointed out, helped transfer of data from Hanle to Bangalore. Sreekantan said: "We have to provide the necessary equipment and environment to encourage young astronomers to do fundamental research. During the last 50 years we have advanced in the fields of cosmic ray research, radio astronomy and space astronomy, but in optical astronomy we have not put in a sufficient amount of investment."

Cowsik hopes that young astronomers will make full use of the facility. The availability of more time for observation will also mean that Indian students pursuing a doctoral degree in astronomy-related areas will now be able to complete it in three years. At Kavalur, it will take at least five years.

Also, the telescope will allow Indian astronomers to interact on a more equal footing with their counterparts all over the world. And it is an acknowledged fact that collaboration is the name of the game in building big telescopes and establishing sufficient infrastructure to locate them. Says Wehinger: "Hanle being the best developed site in the world at high elevation will attract joint ventures. In order to minimise total costs India could provide the infrastructure; and given the lower labour costs here, they could also manufacture the mechanical components. Overseas agencies could provide the optics. Right now there is a great deal of interest in the Chajuantar site in Chile."

The biggest partnership in the world now is the one for the 8.4 m binocular telescope (BT) project, involving Germany, Italy, the University of Arizona, the Ohio State University and the private entrepreneur, Re-search Corporation. Astro-nomers are also examining the possibility of a joint venture for a Rs.350-crore BT project at Hanle. Cowsik said: "We have had long discussions on the BT with Japanese, American groups. But specific proposals can be put forward only after we have decided that we are going forward in a particular way. The process of initiating a major project is a major effort in itself. Several years of efforts are needed." The Union government had told Indian astronomers that if they succeeded in setting up a telescope at Hanle it would consider partly funding bigger projects such as the Hanle BT project.

According to Dr. Russell Cannon, former Director of the Anglo-Australian Obser- vatory in Australia, the uniqueness of the Hanle site could be attractive to Asian countries that are interested in setting up an optical telescope but do not have the right climate for it. Cannon said: "India can step in and offer Hanle. The Japanese, realising the futility of establishing a telescope in their homeland, are building one of the largest optical telescopes in the world. The 8 m telescope called 'Subero', will be located in Hawaii." A collaboration between the IIA and the Macdonell Centre for the Space Sciences, Washington University, St. Louis, U.S. has already resulted in a plan to develop two 50-cm Cassegrain telescope observatories, nearly 180' apart in longitude, at Hanle and in Arizona. The objective of the tie-up is to create a facility that will enable an almost round-the-clock monitoring of transient phenomena. The telescopes are designed to be controlled by a single computer at each location and are to be used predominantly for the continuous photoelectric monitoring of the active galactic nuclei.

Astronomers hope that observations from Hanle will throw more light on cosmology and large-scale structures in the universe, by raising the short-exposure limit to 25 B magnitude.

The Himalayan Chandra telescope could be used for spectroscopy of high redshift radio galaxies and photometry and spectroscopy of supernovae. Observations from a telescope like the one at Hanle could be crucial in another key aspect of research in astrophysics - stellar evolution. But, more than anything else, astrophysicists hope that the Himalayan Chandra telescope will ignite interest in astronomy.

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