Topic G: Stellar Twins (Binary Stars)
- Binary Stars
- Know definition of a binary star — see Study Guide Slide #4
- Know difference between optical and physical double stars
- Know importance of binary stars (3 reasons — see Study Guide Slide #4)
- Which astronomer searched for double stars and why? (See Study Guide Slide #6)
- How did astronomers originally deduce most doubles are physical rather than optical?
(See Study Guide Slide #6-10) - How frequent (common) are binary stars (very common?, not common?, etc.)
- Know which star asterism contains a naked eye double (name?) and how to find it (See Study Guide Slide #12-14)
- Stellar Masses
- What method is used to find stellar masses (M)? (Hint: See Topic B, Kepler and Newton)
–That is, what relation is used to find the sum of the masses in a binary system?
–See Study Guide Question #13 plus extra question at bottom of page - To find each component's mass in a binary, what additional information is needed besides (M1+M2)?
(Ans. mass ratio)
- Be able to find M1 and M2 given their sum and ratio (see Study Guide Question #14)
- Know approximate range of stellar masses (in solar masses) — Ref. Fig. 16 (Note #1)
- The Mass-Luminosity Relation (Ref. Figure 16)
–For which group(s) of stars is the M-L Relation valid? (Ans. Only Main Sequence)
–What does the M-L Relation show? (i.e., What does this graph plot or display?) - Know how mass changes along the main sequence (see Table 13, next to last column)
- What method is used to find stellar masses (M)? (Hint: See Topic B, Kepler and Newton)
- Stellar Densities
- Definition of mean stellar density
- Which stellar quantity (i.e., mass or volume) causes density to change most? Why?
- Know how density varies along the main sequence (see Table 13, last column)
- Know how density differs for giants, supergiants and white dwarfs
- Properties of Main Sequence Stars (Ref. Table 13)
- Know all trends shown in Table 13
- That is, know how each parameter changes from early to late main sequence stars
(incl. temperature, radius and luminosity, mass and average or mean density) - Questions following the HR Diagram in Figure 13b (not in printed Study Guide) supplement material you should know about the HR Diagram, masses and densities
- Tentative List of Study Guide Questions To Omit for Topic G
- Do 7 through 9, 13 through 14, 16 through 20, 22 through 25
- Omit #1 through 6, 10 through 12, 15, 21
- Here is an extra Harmonic Law question to try:
A binary star has an orbit period of 60 years and a semimajor axis of 30 astronomical units. What is the sum of the two stellar masses (M1+M2) in this system (in solar masses)?
(1) 0.25 solar masses (2) 0.5 solar masses (3) 2 solar masses (4) 5 solar masses (5) 7.5 solar masses
Click for Answer
* This list is reasonably complete but students remain responsible for all material presented in class. Tables, figures, examples, etc., listed here refer to Study Guide items.
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