A Wide Range of Observations At Kavalur


Observations at Kavalur include several exciting phenomena: lunar occultations of stars; distribution of young stars in galactic spiral arms; variable stars, stellar atmospheres and composition, and extragalactic structures and spectra of the nuclei of galaxies, comets and asteroids. A computer-controlled data archival system maintains a unique record, which is open to scholars. A glimpse of some of the observations made would indicate the range of programmes.

In the area of solar system research, the programmes include observations of comets, eclipse events of the Jovian satellites and search and studies of asteroids. A dramatic display in the images was the ejection of gas and dust in the form of jets out of the nucleus of the comet Swift-Turtle. The series of exposures showed that the cometary nucleus rotates with a period of 2.7 days. Studies at the Vainu Bappu Telescope (VBT) showed that in comet Austin, the dust grains in the coma are larger than in the tail. The most spectacular image was taken in July 1994, when comet Shoemaker-Levy 9 collided with the planet, Jupiter, another observation was the deep impact crater created by a NASA probe on the comet Tempel 1 in2005. Other images include those of Galilean satellites of Jupiter, whey they occult each other.

In stellar and galactic astronomy, visible manifestations of the star-forming regions were studied. Star clusters, which can reveal the structure and evolution of the Milky Way and other galaxies are studied at the prime focus mirror of the VBT. Much attention is paid to the determination of chemical composition of stars. Monitoring a number of extragalactic supernovae—resulting from exploding massive stars at the end of their lives—has been another activity.

The big telescope at the VBT has been extensively used for spectroscopic studies of stars in the late stages of evolution as well. The role of dust and its condensation, mass loss and the distribution of gas as well as the mixing of several chemical elements are some of the other aspects of interest in the studies in spectroscopic and imaging modes. Hydrogen-deficient stars, spectra of many stars, oscillations of white dwarfs, close binaries with dwarf companions have been some of the other research topics. Moreover, the mysterious diffuse interstellar bands—discovered some 70 years ago—were also probed.

The VBT has been used for studying star-forming regions of nearby galaxies as well. Other studies included imaging of elliptical galaxies on the basis of their radio and X-ray properties, accretion and merger events, formation of massive stars in the giant extragalactic HII regions. In another interesting study, the radio galaxy 3C 270 (NGC 4261) showed the presence of a dust lane oriented close to the major axis of the galaxy. The line is interpreted as the projection of a disc inclined at 75º to the plane of the sky and perpendicular to the radio axis. The disc could be the source of gas to the nucleus that triggered the nuclear activity.

The observatory has another programme, designed to study the Earth’s equatorial thermosphere. An instrument, known as the Fabry-Perot interferometer, captures the airglow emissions from the night sky. The device makes use of multiple reflections between two closely spaced surfaces to provide extremely high resolution. The interferometer isolates the emission line, which is at 630 nm. This high-resolution spectroscopy provides valuable inputs in understanding the features of the thermosphere near the equator.

State-of-the-art computer facilities are made available at Kavalur, where the data from various telescopes are stored. Indian astronomers also participate in the multi-wavelength study of celestial objects by combining their data with that obtained by foreign satellites.

Two monsoons in a year hitting Kavalur have made observations almost impossible during several months. As Indian astronomers gain more and more experience, they naturally yearn for a fuller participation in the international efforts in studying astronomical phenomena from several locations in real time. It is increasingly realized that a new, suitably located India telescope could take full advantage of the country’s ideal location in the southern hemisphere spanning the vast area between longitudes 20º West and 160º East.

Astronomers at Kavalur face the problem of water vapour in the atmosphere, besides increasing air pollution. It is typically more than 10 mm and it absorbs some of the infrared radiation from the astronomical objects. In the days when the big telescope at Kavalur was still on the drawing board, the noted astronomer, J.C. Bhattacharya, used to proudly say that the site and its environs had hardly any human footprints that would spoil the quality of the images. That hope, it is feared, may well go up in smoke that emanates from the increasingly dense human settlements near the telescope complex, unless timely action is taken.

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