Name:_____________
                                                                                                                      
                                                                                                      TA:_____________
                                                                                                                      
                            AY2 Homework Set 6
                                                            
                                                     Due 05-14-02
 
Answer all of the five questions.  Show your work for the problems that need math.
Useful formulas:
       T = 3 x 10-3 m K
                          l
             L = 4ps R2 T4
     
            B= L/( 4p D2 ) 
 
            m-M = 5 log( d/10)    m=apparent magnitude, M=absolute magnitude, d=distance        
 
1-         The spectral type of stars: the continuum
    a-      draw a simple graph, making a sketch of the three black body radiation curves,  one each for
    the temperatures 2000K, 6000K, 10000K . Show the approx. values for the wavelength and temperature.
    b-     Indicate the spectral region (for example, blue, infrared, x-rays)
    c-      Which curve best represents the sun ( remember that the sun is highly visible) 
 
 
 2-        Explain why nuclear fusion takes place only in the center of stars rather than in their surfaces as well. 
What is the major fusion process that takes place in the Sun?  What is the temperature under nuclear fusion takes
place in the sun?  How many times hotter is the core relative to the surface?   (check in the book for the sun?s
temperature in the center and surface).
 
 
3-         Using an H-R diagram from the book and other concepts let?s answer the following questions about five
stars
       1                      2                      3                      4                      5
Type    G0 III              B0 V                F0 I                  M0 III              K0 V
m          0                     20                    3                      12                    5
(apparent magnitude)
    a-      Which one is the hottest/coldest?
    b-     Which one is the most/least luminous?
    c-      Which one is the closest/ farthest star?
     
 
 
4-         Let?s compare the star Sirius (the dog star in the constellation Canis Major or big dog) to our Sun. 
a)         The surface temperature of Sirius is about 10000 K and the temperature of the sun?s surface is about 6000
K.   We also know that Sirius?s diameter is just 3.6 times the diameter of the sun.   So, what is the ratio (how much
more luminous) of Sirius?s luminosity to that of the sun?s?
b)         If Sirius is 550000 times farther away than the sun, how much Brighter (now you compare brightness) is our
sun compared to Sirius.
For Romans and Greeks this star was blame for the extreme heat of July and August thinking that it added brilliance
to the sun.  This is why in hot days of late summers we call the as ?Dog Days?. 
 
 
5-         Short answers: What is the source of energy in a collapsing protostar?
                                  When the protostar becomes a main sequence star?
                                   When the end of a main sequence star occurs?