Homework Set V

                          (Due by May 8th at noon)


Solve the following 5 problems and show all your calculations. 
Remember to write the name of your TA on your homework.



1)    Consider a star whose wavelength lambda_max, corresponding to the
maximum intensity, is double that of the Sun and whose radius (R_s) is
10 times that of the Sun. What is the luminosity of this star compared to the
luminosity of the Sun?



2)    The star Proxima Centauri has the largest known parallax angle,
equal to 0.772 arcsec. What is its distance from Earth in ly (light years) ?
Do you know the name of the closest known star to us (except the Sun) ?



3)    Describe the basic features of the theory for the formation of a
planetary system. Provide as many details as you can.



4)    Two stars, A and B, of absolute magnitude 9 and 4 respectively
(M_A = 9 and M_B = 4) are observed to have the same apparent magnitude. 
Which one is more distant ? 
How much farther away is one than the other ?


5)    A typical Cepheid variable star is 100 times brighter than a
typical RR lyrae star. How much farther away than RR Lyrae can Cepheids be
used as distance measuring tools ?


Useful equations:



L = 4 sigma R^2  T^4

m1 - m2 = 2.5 Log( B_r1 / B_r2 )

T = 2.9 x 10^6  K nm / lambda_max

B_r =  L / (4 pi D^2)

v_r / c = (lambda_observed  - lambda_lab) / lambda_lab

p = 1 / d (when d is in units of parsecs and p is in units of arcsecs)