Department of Physics, Panjab University, Chandigarh, India

TPSC seminar

Date and time: 2 August 2013 (Friday), 4:00 pm
Venue: Seminar Hall

Title: Technological evolution in observational astronomy

Speaker: Prof. S.K. Saha, Formerly with Indian Institute of Astrophysics, Bangalore

Abstract: In order to get information of the structure of a star and its evolutionary history, astronomers had to invent the telescope and many other instruments. Also, they have developed sophisticated techniques to analyse the observations. These equipment are being used to study close binary stars, atmospheres of stars and brown dwarfs, galactic and extragalactic star formation, late stages of stellar evolution including AGB and post-AGB stars and their chemical compositions, planetary nebulae, novae and supernovae, structure of nearby galaxies, quasars and active galactic nuclei (AGNs) etc. With the present day technology, there are plans to built very large telescopes of 30 to 40 m in diameter. A telescope of this kind helps in gathering more optical energy, and also in obtaining better angular resolution. However, the image quality of an optical telescope is marred by the atmospheric turbulence which limits the resolution of large telescopes. Large telescopes, equipped with conventional mode of spectroscopy/imaging method, cannot achieve diffraction-limited information. Speckle interferometry, a post processing technique, has made inroads in several important fields in astrophysics. Another development in this direction is the adaptive optics system, which improves the performance of telescopes by correcting the degraded image in real time. However, in the optical band, a large mirror of >10 meter class with a high precision accuracy in figuring may not be possible to develop. Introduction of long baseline interferometry using diluted apertures became necessary and the improvements of instrument technology made it possible to obtain a very high resolution of the order of a few milliarcseconds. The interferometry with phased arrays of multiple large sub-apertures has become a reality. These instruments are used to obtain results from the area of stellar angular diameters with implications for emergent fluxes, effective temperatures, luminosities and structure of the stellar atmosphere, dust and gas envelopes, binary star orbits with impact on cluster distances and stellar masses, relative sizes of emission-line stars and emission region, stellar rotation, limb-darkening, and astrometry. However, in order to obtain snapshot images of the astronomical sources, many-aperture optical array with arbitrarily diluted apertures is required to be built; hypertelescope approach to imaging is an emerging concept, which has a vast potential. This lecture is aimed to describe some of these techniques and methods.