Astronomy and Astrophysics — DU B.Sc. (Hons) Physics Previous Year Question Papers

2. Attempt five questions in all. (a) Show the location of the Sun on Winter Solstice (Dec 21-22) in a diagram of equatorial coordinate system. What are Sun's declination and right ascension on this day? - (b) Draw the right tracks of stars for an observer at Equator. Show the track of the Sun on Summer solstice for this observer, and locate the position of the sunrise and sunset on her horizon. (c) If the mininum measurable parallax angle for a certain instrument is 10 arcseconds, what is the maximum distance at which the instrument can measure an object's parallax if (a) the baseline is equai to the Earth's diameter about 12,500 km and (b) the baseline is diameter of the Earth's ori (d) The brightest stors are around 10° times brighter than the Sun. If the apparent magnitude of these bright stars in a galaxy is 22.5, how far away is the galaxy? (e) The apparent morer of the Sun is 32' (arc-minutes) and the flux of solar radiation received on! 170 W/m?. What is the flux density at the surface of the Sun? (f) Determir lure of c in the density profile (o(r) o r*) for a spherically symmetric mass distril •f-t rotation curve. (g) Given that a globular cluster is 14 Gyr old, what is the upper limit on tir: Hubble constant in units of kms-1Mpc™1, assuming that the rate of expansion of the Universe has remained constant? 2 )Don teren and ordinate ate the brio de die or a digen (b) Show the hour angle of a star X on the local equatorial coordinate syster: of an observer at latitude . The local sidereal time (LST) is defined as the hour angle of the vernal equinox. Prove that for a star X, HAX = LST - RAX, where HAX is the hour angle of X and RAX is its right ascension. (c) What are circumpolar stars? A star has declination 8= 40°. If it is viewed from a point on the Arctic Circle (66.7°N) what are its maximum and minimum zenith distances? 3. (a) The shadow of a 2 m tall pole at a place is 1 m on the noon of winter solstice, when the Sun is at its highest point in the sky. What is the latitude of the place? (b) Discuss the classification of stars based on their temperature and luminosity. Draw the main sequence, red giant and super giant branches on an HR-diagram. Why are He lines prominent in O type stars and absent in K type stars? (c) Draw the cosmic distance ladder. What are type la supernovae and how are they used to estimate astronomical distances? 4. (a) The Sirius is a visual binary star system with components Sirius A and Sirius B. It has annual parallax of 0.38" (arcsec). The largest parallax of the separation between the two components is 12", and the minimum is 3". What is the semi-major axis and eccentricity of the relative orbit? The orbital period is found to be 50 years. What is the total mass of the system? If the semi-major axis of the obit of Sirius B is double of that of Sirius B, find values of their individual masses.