Suppose you observe a tight eclipsing binary with orbital period of 3 days, and radial velocity semi-amplitude for both components of 80 kilometers/second. a. Without doing any calculation, you know that the mass ratio of the binary is 1:1. Explain why? b. What are the masses and orbital radii of the two stars? c. Suppose the binary is perfectly aligned so each eclipse the center of one star goes across the other. How often do you see an eclipse? d. Suppose one eclipse lasts for 3.5 hours. What is the radius of the stars?

How high or low a star is on the main sequence is dictated primarily by ... Select one: A. its chemical composition B. the fraction of metals in its atmosphere C. what elements are fusing in its core D. the size of its photosphere E. its mass

Which statement is most logical?  a Once gravity overcomes thermal pressure, nebulae cloud turns into molecular cloud. If it is cold and dense enough, molecular cloud might turn into protostar.  b If gravity is stronger than thermal pressure, nebulae cloud contracts into molecular cloud. If it is cold and dense enough, molecular cloud might turn into protostar.  c If a molecular cloud is cold and dense enough, it turns into a protostar. Once gravity overcomes thermal pressure, protostar might become molecular cloud.  d If a nebulae cloud is cold and dense enough, it turns into molecular cloud. If gravity is stronger than thermal pressure, molecular cloud might become protostar.

Based on what you learned about stellar evolution, select all of the correct statements from the following list.   1. The period of some Cepheid variables actually changes. 2. When getting dimmer, variable stars are releasing energy; when getting brighter they are storing energy. 3. variable stars are expanding and contracting 4. despite their variability, variable stars stay in a specific position on the H-R diagram. 5. A changing period in a Cepheid variable means that the size of the star is changing and that the star is therefore evolving. 6. Only stars on the instability strip are variable. 7. More massive stars will vary their brightness more quickly.

Which of the following statements is wrong? A. A main-sequence star is cooler and brighter than it was as a protostar.  B. Carbon fusion occurs in high-mass stars but not in low-mass stars because the cores of low-mass stars never contain significant amounts of carbon. C. when a main-sequence star exhausts its core hydrogen fuel supply, the core shrinks while the rest of the star expands. D. After a supernova explosion, the remains of the stellar core will be either a neutron star or a black hole.

Which stars have the longest period of variability?   a. RR Lyrae   b. Type I (classical) Cepheids   c. Type II Cepheids   d. main-sequence stars   e. All have the same period.

An eclipsing binary will   a. be more luminous than a visual binary.   b. always be a spectroscopic binary.   c. give off most of its light in the infrared.   d. show a constant Doppler shift in its spectral lines.   e. show two stars with variable proper motion.