If a binary star is observed from directly above the orbit it cannot be detected as a spectroscopic binary. The faintest stars that can be seen in the sky with unaided eye have magnitue of 2. Star A has an apparent magnitude of 11, and star B has an apparent magnitude of 6. The absorption lines in a stellare spectrum provide information on a. the radial motion of the star. For an eclipsing binary we observe the minimum amount of radiation from the system when a. the two stars are side by side as seen from the Earth.
Binary stars provide astronomers with their primary method for measuring stellar a. luminosity.
The absorption lines of hydrogen are weak in the hottest stars because a. they have consumed most of their hydrogen. We see some binaries as spectroscopic and others as eclipsing systems. The quantity that makes them different is their a. orbital shapes. The statement is backward. Low-mass stars are more luminous.