Q:  What is the orbital speed of the helium star B?

        First, we compute the gravitational acceleration of helium star
        due to its white dwarf companion.

                           G m_A
               accel  =   ----------   
                             a^2


                      =   5230  m/s^2



        Next, we determine its centripetal acceleration.


                             (v_B)^2                 (v_B)^2 
               accel  =   -----------   =   -----------------------------
                              R_B             a * [ m_A / (m_A + m_B) ]


                              (v_A)^2
                      =    ------------------
                             1.53 x 10^(8) m



  Q:  Solve for the velocity of star B.


                                   
                 v_B   =    sqrt (  5230 m/s^2 * 1.53 * 10^8 m )


 
                       =    8.92 x 10^(5) m/s   =   892 km/s