ASTROPHYSCL PROCESS ASTRO 405
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This 2 page Class Notes was uploaded by Solon Leuschke on Sunday September 27, 2015. The Class Notes belongs to ASTRO 405 at Iowa State University taught by Staff in Fall. Since its upload, it has received 24 views. For similar materials see /class/214521/astro-405-iowa-state-university in Astronomy and Astrophysics at Iowa State University.
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Date Created: 09/27/15
Astro 405505 fall semester 2005 Additional problems Problem 1 plasma You intend to study a gas cloud that collapses to form a star Suppose the cloud has a radius R 1015 cm a temperature T 1000 K a density of neutral atoms 72 1012 cm g and a density of ionized atoms and electrons n6 108 cm g Explain with what technique you would describe the collapse Problem 2 emission spectra Suppose an emission region is homogeneous and the radiation coef cients have the following form j AV 1 04 B V73 0 0 A B const Calculate the angular distribution of the intensity ID that would be seen by an observer at a xed position at a distance D from the emission region and the total flux a Assume the emission region has the form of a cube with sidelength R that is observed exactly along the normal of one of the sides b Assume the emission region has the form of a sphere with radius R Problem 3 stellar emission The conditions in stellar photospheres are often well represented by a Local Thermodynamic Equilibrium LTE Neglecting scattering please derive a quantitative estimate for the angular distribution of the intensity ID that would be seen by an outside observer a Assume the temperature T is constant independent of the vertical optical depth which itself is assumed independent of frequency b Assume the temperature is constant in each of three zones with values To OSDSH TTz 2To 73913 739 S 7392 4T0 TQSTZ Problem 4 pinhole camera A pinhole camera consists of a small circular hole of diameter d on the front side of a box which is at a distance L from the lm plane on the back side of the box Ifd denotes the angle to the optical axis perpendicular to the front and back planes of the camera show that the flux at the lm plane depends on the intensity eld 167 g5 as 7r cos4 F11 ll67 Problem 5 radiation transport Consider a cloud of gas in LTE with temperature Ty and diameter and thickness D box geometry Assume emission and absorption processes for continuum and lines to operate in the cloud Derive the solution of this radiation transport problem and discuss it for the limiting cases of very large and very small optical depth Suppose a background star with Te gtgt Tg was located behind the gas cloud What would the spectrum of the star look like Problem 6 Review questions a What conservation laws do the hydrodynamical equations describe b What is the di erence between intensity and flux c How would you estimate the level occupation density of hydrogen in the solar photosphere and in a diffuse interstellar gas cloud Can the two be treated the same way d Why do accretion disks form and how do they help the accretion of matter on compact objects e What is the color of blackbody radiation f What can you say about the directionality of the radiation eld if the scattering optical depth 7390 5 d3 03 is very large and absorption is inef cient
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