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PHE-15 ASSIGNMENT BOOKLET Bachelor's Degree Programme (B.Sc.) Astronomy and Astrophysics Please send this assignment to: Prof. Vijayshri Course Coordinator, PHE-15 School of Sciences, Room No. 128, Block D, New Academic Complex IGNOU, Maidan Garhi, NEW DELHI 110068 (Valid until June 30, 2008) School of Sciences Indira Gandhi National Open University Maidan Garhi, New Delhi-110068 2007-08 Dear Student, We hope you are familiar with the system of evaluation to be followed for the Bachelor’s Degree Programme. At this stage you may probably like to re-read the section on assignments for Elective Courses in the Programme Guide that we sent you after your enrolment. A weightage of 30 per cent, as you are aware, has been earmarked for continuous evaluation which would consist of two tutor-marked assignments (TMA) for this course. Instructions for Formatting your Assignments Before attempting the assignment please read the following instructions carefully: 1) On top of the first page of your TMA answer sheet, please write the details exactly in the following format: ENROLMENT NO.:…………………………………………… NAME :…………………………………………… ADDRESS :…………………………………………… …………………………………………… …………………………………………… COURSE CODE: ……………………………. COURSE TITLE : ……………………………. ASSIGNMENT NO. ………………………….… STUDY CENTRE: ………………………..….. DATE:.…………..………………………………... PLEASE FOLLOW THE ABOVE FORMAT STRICTLY TO FACILITATE EVALUATION AND TO AVOID DELAY. 2) Use only foolscap size writing paper (but not of very thin variety) for writing your answers. 3) Leave 4 cm margin on the left, top and bottom of your answer sheet. 4) Your answers should be precise. 5) While solving problems, clearly indicate the question number along with the part being solved. Be precise. Write units at each step of your calculations as done in the text because marks will be deducted for such mistakes. Take care of significant digits in your work. Recheck your work before submitting it. 6) This assignment will remain valid until June 30, 2008. We strongly feel that you should retain a copy of your assignment response to avoid any unforeseen situation and append, if possible, a photocopy of this booklet with your response. We wish you good luck. 2 Tutor Marked Assignment 1 Astronomy and Astrophysics (PHE-15) Course Code : PHE-15 Assignment Code : PHE-15/TMA-1/2007-08 Max. Marks : 100 Note: The marks for each question are indicated against it. Symbols have their usual meanings. 1. (a) (b) Express the distances of the stars Sirius A and Antares in light years. (5) Explain what you understand by apparent magnitude of a star. How is it related to the brightness of the star? An object A has an apparent magnitude of –5. Another object B has an apparent magnitude of –10. Calculate the ratio of their brightness. (1+1+3) 2. (a) Define and sketch a great circle and a small circle. Must they be parallel always? Explain.(5) (b) Sketch the celestial equator, horizon, observer’s meridian and show the zenith and nadir on the celestial sphere for an observer at latitude 30 N. (5) 3. (a) (b) 4. (a) (b) The latitude and longitude (in degrees) of Mumbai and Shillong are as follows: Mumbai: latitude 19 N longitude 73 E Shillong: latitude 26 N longitude 92 E. When it is 12:00 O’clock local time at Shillong, what is the local time in Mumbai? Explain why sidereal day is shorter than the solar day. What is the magnitude of this difference? What effect does this have on the rising of stars in the evening? (b) 6. (a) (b) (c) 7. (a) (b) (c) 8. (a) (b) 9. (a) (b) (5) Compare the resolving powers of a 1 m optical telescope at 550 nm and a radio telescope at 3 cm. (5) Calculate the diameter of a telescope which could detect objects up to a visual magnitude of 27. 5. (a) (5) (5) The average density of a white dwarf of radius 109 cm is 106 gm/cm3. Is general theory of relativity needed to study the dynamics of this star? What happens if the star shrinks to a radius thousand times smaller? (5) Define the pressure of a radiation field. Show that for an isotropic radiation field the radiation pressure is (4/3c) times the specific intensity. (5) What is the nature of radiation generated in the Sun’s interior? How does it differ from the radiation we receive from the Sun? What causes granulation of the photosphere? (1+1+3) Explain why the temperature of sunspots is lower than their surroundings. What is the butterfly diagram? (3+2) Explain helioseismology. How does it help in understanding the internal structure of the Sun? (2+3) What are the main differences between the terrestrial and jovian planets? How does the ring system of jovian planets persist for so long? (3+2) What is solar nebula? Explain the formation of nebular disk. (2+3) Discuss the three stages of the formation of planets from the solar nebula. (5) Explain the atomic origin of emission and absorption spectra. (5) What is the contribution of M.N. Saha in the classification of stars? Explain with a few examples. (3+2) Write down the order of magnitude by which the internal temperature of the Sun is higher than its surface temperature. Explain the energy generation process at the core of a star. (1+4) Show that for a polytrop, P Pc n 1 where Pc is central pressure and n is polytropic index. 3 (5) Tutor Marked Assignment 2 Astronomy and Astrophysics (PHE-15) Course Code : PHE-15 Assignment Code : PHE-15/TMA-2/2007-08 Max. Marks : 100 Note: The marks for each question are indicated against it. Symbols have their usual meanings. 1. (a) What are the characteristic features of the H II region of ISM? How is it different from the molecular cloud? (3+2) (b) Explain the phenomenon of interstellar extinction. What information does it provide regarding the composition of ISM? (3+2) (c) Explain the free fall collapse of an interstellar cloud? Show that the free fall time of a collapsing cloud is a function of the initial density of the cloud. (1+4) 2. (a) What is cosmic abundance? How does it relate to the solar system abundance? How do you differentiate between population I and population II stars? (2+1+2) (b) Discuss p-p chain reaction. How does it differ from CN-cycle? What can we infer about the composition of a star if CN-cycle is active in it? (2+1+2) 3. (a) Explain the concept of degeneracy pressure. What role does it play in the evolution of a star after its death? (3+2) (b) What is planetary nebula? Explain the concept of Chandrasekhar limit. (2+3) (c) The mass and radius of a neutron star is 2M and 15 km, respectively. Calculate the value of gravitational red shift for light of wavelength 6000 A at a distance of 2 m from its surface. (5) 4. (a) Explain the difference between rigid body rotation and Keplerian motion. What is galactic longitude? (4+1) (b) Discuss the rotation curve of our Galaxy. What inferences can be drawn from it about the structure of our Galaxy? (3+2) 5. Explain Hubble’s scheme of galaxy classification. Describe the prominent features of spiral galaxies. (5+ 5) 6. (a) Explain why we expect the gas in elliptical galaxies to be hot. (b) 7. (a) (b) 8. (a) (b) 9. (a) (b) (5) What is synchrotron radiation? Explain why synchrotron radiation from AGN is largely linearly polarised. (2+3) Calculate the half-width of a spectral line of wavelength = 550 nm when the temperature of the gas is 6 105 K. Assume H atoms to be emitters. (5) Explain the origin of broad-line and narrow-line regions in a Seyfert galaxy. (5) Describe the nature of the central engine in an AGN. (5) Explain the concept of a distance ladder. (5) Explain why at one time, the steady state theory appeared necessary. What is its status now? (5+2) Explain the need to postulate the existence of dark matter in the universe. 4 (3)