Look at Russell's diagram:
  there is one dot at

     apparent magnitude (roughly) V = +11

     (roughly) T = 10,000 K


  Q:  What is the luminosity of this star?
      Express your answer in Watts, and in terms
      of the solar luminosity (3.8 x 10<sup>26</sup> Watts).


              L(star)        0.4*( M(sun) - M(star) )
            ----------  =  10
              L(sun)
                             0.4*(  5  -  11 )
                        =  10                    

                             0.4*(-6)  
                        =  10           =  0.004   =  1/250


            So this star has only 0.004 solar luminosities.
            Since the Sun has a luminosity of L(sun) = 3.8 x 10^(26) W,
            we can calculate


             L(star)    =  0.004  *  L(sun)

                        =  0.004  *  3.8 x 10^(26) W

                        =  1.5 x 10^(24) W