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Winter School in Astronomy, IIST, Dec '13 - An overview

Note : The words introduced, discussed and commented appear a lot, A LOT, in the following post. I couldn't come up with a better way to concisely write about what we (i) was taught during the school. I've tried (been trying for over an year) to write a detailed report of the the topics discussed by each of the professors but i thought this would atleast get the wheels in motion.

6 Professors from the Earth and Space Sciences department of IIST, Trivandrum conducted the winter school. It was a 2 week school, theory sessions in the morning and lab sessions in the evening. The school was primarily oriented towards giving a theoretical overview of (interesting) astrophysics, the lab sessions were just an added bonus to screw around with linux machines and a chance for the (participant) unix nerds to show off their comfortness with the terminal.

The school started off with Prof. Anandamayee talking about (an adapted version of) the scale of the universe, giving interesting anecdotes and examples at different points. Starting with the clouds, rainbows, moon, sun and eventually the milky way galaxy. She then talked about the celestial coordinate systems and introduced some of the basic definitions in astronomy such as the distance to a star/object, the flux of the object, it's absolute & apparent magnitude (m & M) and how each of these quantities are related to each other. Stellar spectra were introduced, the differences between emission and absorption spectra pointed out and concepts such as equivalent widths of the emission/absorption lines, their peak broadening were introduced. The HR diagram was discussed.

Prof. Sarita Vig talked about telescopes, their defining parameters such as aperture size, plate scale, f number and the like. She went on to talk about the differences between telescopes used for different parts of the electromagnetic spectrum. Moving ahead, the Interstellar medium was discussed, introducing topics such as extinction, reddening and polarization. Correction factor to the m-M relation was defined using optical depth. Star formation was discussed, introducing the various phases of ISM, the difference between molecular gas clouds and hot ionized plasma in space, interstellar extinction curve and the importance of dust in the formation of stars were discussed.

Broadly defined as Astronomical Techniques, Prof. Jagadheep talked about the Photometry, Spectroscopy, Interferometry, Astrometry & Polarimetry. Photometry covered a description of the popular broad band filters (U,B,V,R,I), the definition of colors and the construction of the HR diagram with the use of the colors. The saha equation and the use of gratings were covered in spectroscopy. Cross-correlation between two (radio) receivers was defined in interferometry. Astrometric conventions were introduced and finally, phenomenon such as faraday rotation, zeeman splitting and stokes V spectrum were introduced in polarimetry. Stellar formation was next, starting with the study of a molecular cloud in hydrostatic equilibrium, the Jeans criterion for collapse of the cloud, the Bonnor-Ebert spheres and the typical size, mass & temperature of the cloud at different phases of collapse were calculated. For an interesting read, look up Kevin-Helmholtz time.

Prof. Resmi Lakshmi talked about Special Relativity and the various Radiation processes in astrophysics. Relativistic beaming, relativistic doppler effect and general relativistic 4 dynamics were introduced. The concept of retarded electric and magnetic fields, larmor formula & the synchrotron emission, bremsstrahlung were discussed. The very peculiar Gamma ray bursts, their origin, propagation of the jets were further discussed with interesting comments on how the first gamma ray bursts were indeed discovered by cold war spy satellites.

The evolutions of stars was discussed by Prof. Samir Mandal, phases of stellar evolution and use of the HR diagram to infer the age/type of star.  The standard spectral classification of stars; O,B,A,F,G,K,M; and the mean mass & luminosity of stars belonging to these spectral classes were introduced. Equations governing hydro-static equilibrium in a star and various energy transport processes in a star, differing depending on the age, were discussed. The source of stellar radiation i.e atomic fusion and the various nuclear reactions that occur at stellar cores at various ages were commented upon. Back of the envelope calculations to estimate mass of stars at various stages of nuclear fusion i.e H burning, He burning, C burning and so on were done. And finally, the death of a star and the series of events that take place in it's core were briefed on. Following the generic discussion of stellar life cycle, the peculiar objects such as white dwarfs, neutron stars and black holes were introduced.

Last but not the least, Prof. Anand Narayanan talked about Galactic and extra-galactic astronomy. The various types of galaxies and their components, morphology and kinematics of galaxies was introduced. Starting from molecular dust and the distribution of gases to the percentage in mass of stars to the galactic mass and peculiar objects in galaxies such as supernovae, nebulae, open & globular clusters and finally stellar & galactic jets were discussed. The concepts of photo-ionization and recombination, absorption cross-section were introduced. The use of standard candles in distance measurement and corrections to hubble's distance measurements due to interstellar reddening were commented on. Methods to estimate inter-stellar distances such as trigonometric parallax, moving cluster method, photometric distance estimation and stellar pulsations/variable stars were discussed. The tuning fork or the hubble classification of galaxy types was introduced. The kinematics of a galaxy and the use of spectroscopy to infer the rotation curve of the galaxy (due to differential rotation) was discussed. The differences between the theoretical rotation curves and observed rotation curves leading to the "discovery" of dark matter in galaxies was pointed out.

We were pointed towards some interesting popular reading material on astronomy -

  • 'Fundamental Astronomy' by Kartunnen,
  • 'Astrophysics for physicists' by Arnab Rai Chaudari, 
  • G. Srinivasan's books "What are stars?", 'Can stars find peace?',
  • "Astronomical Spectroscopy" by Jonathan Tennyson,
  • 'The alchemy of heavens' by Ken Crosswell and 
  • two biographies of the famous Prof. S. Chandrasekhar by Radhika Ramnath and Kameshwar C. Kali.
Additions and edits to follow but this is enough to start. 
I guess...

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