This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: AST 3722C  Spring 2008 Homework #7 – Due before class March 25 Instructions: Solve each part of each problem below. Where math is involved, and unless otherwise indicated, show your work. • 1. (1 point.) The star β Cyg is actually a double star. (a) Let subscripts 1 and 2 refer to the two stars. In Bband, the stars have magnitudes m B 1 = 4 . 171 and m B 2 = 5 . 027. Which star is fainter and by what factor in flux density? (b) In Vband, the stars have magnitudes m V 1 = 3 . 085 and m V 2 = 5 . 088. Which star is fainter and by what factor in flux density? (c) Use these numbers to figure out and explain which is the bluer (hotter) star, 1 or 2? • 2. (3 points.) Suppose you are looking at a star – call it “A” – that provides a flux density F A ( λ ) such that: F A ( λ ) = C A × parenleftBigg 1 μ m λ parenrightBigg 3 . 97 , where λ is the wavelength and C A is a constant with dimension power per area per wavelength interval. Nearby, a new object has appeared in the sky – call it “B” – and very conveniently you can take pictures of B while A is in the same FOV. You observe the two objects at several wavelengths and measure the following differences in magnitudes between A and B: Wavelength m A − m B ( μ m) (mag) 1.2 μ m10.058 1.6 μ m5.730 2.2 μ m2.282 3.6 μ m 1.115 5.0 μ m 2.498 8.9 μ m 3.904 9.7 μ m 4.040 10.6 μ m 4.166 11.7 μ m 4.291 12.5 μ m 4.366 18.7 μ m 4.714 20.6 μ m 4.776 (Of course there are uncertainties on these magnitudes but ignore those for now.) (a) Calculate F B , object B’s flux density, at all 12 wavelengths in terms of C A . (b) Make a semilog plot of wavelength versus F B . Since C A is in all values of F B , you can assume C A = 1 (in proper units), or anything you want for that matter. You should see that the plotted points more or less trace out a Planck function....
View
Full
Document
This note was uploaded on 11/09/2009 for the course AST 4700 taught by Professor Fernandez during the Spring '09 term at University of Central Florida.
 Spring '09
 Fernandez
 Astronomy

Click to edit the document details