Question : 77.To observe a visual binary, we must measure radial velocities. 78.The : 1777235

77.To observe a visual binary, we must measure radial velocities.

78.The more massive star in a binary system is always farthest from the center of mass.

79.If a binary system has a period of 4 years and a separation of 5 AU, then the total mass is 7.8 solar masses.

80.To observe a spectroscopic binary, we must be able to see both stars individually.

81.We can find the masses and diameters of stars that are in eclipsing binary systems.

82.When we see a binary system producing eclipses, we know that the orbit is nearly edge-on.

83.The most massive main-sequence stars are the M stars.

84.The densest stars in the H-R diagram are the white dwarfs.

85.An M star is hotter than an O star.

86.On the H-R diagram, lines of constant radius slants down from left to right.

87.The luminosity of a star is the total amount of energy it radiates each second.