2. Learning Goals:
4. Complex Knowledge: demonstrations of learning that go aboveand above and beyond what was explicitly taught. 3. Knowledge: meeting the learning goals and expectations. 2. Foundational knowledge: simpler procedures, isolated details, vocabulary. 1. Limited knowledge: know very little details but working toward a higher level.
How do stars differ from moons and planets, and from one another?
How does the classification of stars help us understand how they evolve over their lifetimes?
What are the different types of stars?
What happens when different types of stars die?
Why is it important for us to understand stars?

3. One last subject before your test tomorrow!
Multiple star systems….
2 or more stars orbiting each other
Much more common that we originally thought

4. Importance of binary stars
They are common
Half of all star systems have two (or, occasionally, more than two stars)
So 3/2 of all stars are in multiple systems!
Stellar masses
It is very difficult to determine the mass of an isolated star
Can determine masses in binary system from analysis of the orbit
Most of our knowledge of stellar masses comes from binary systems

5. Binary Stars -
Binary stars are pairs of stars orbiting each other “connected’ by their mutual gravitational interaction.
50% of stars are binaries: ~100% O/B ~75% M Obs. biases

6. Binary Stars -
Binary Stars may have orbital periods from seconds to hours to thousands of years
They may contain stars of all kinds, sizes, and masses
They may have circular or elliptical orbits
They are usually believed to have formed together - same age (not capture)
Close binaries affect each other’s evolution
Long period binaries essentially act as single stars

7. Binary Stars Half the stars in the sky are binary stars!
Many stars look like they are binaries, but are really not: they are optical doubles.
Fortunately, many other are true binaries, even if they’re too close together to be resolved.
Binary systems are called different things, depending on how we perceive them. A true double star can be called a visual binary, a spectrum binary, a spectroscopic binary, an astrometric binary, and/or an eclipsing binary, depending on what we see.

8. Binary Stars - Types
Binary stars come in a few types differentiated by their orbital period and/or observational behavior. For example:
Visual double (actually see both components - LONG period). Do not confuse with optical double
Astrometric binaries - see the wobble on the sky
Eclipsing binaries - one/two eclipses per orbit
Spectrum binaries - spectral properties change
Spectroscopic binaries - radial velocity –ie. Doppler effect motions (short periods easier to find)

9. Visual Binaries Castor
When both stars can be seen, it’s called a Visual Binary.
Castor

10. Visual binaries
A visual binary system is a system in which two separate stars are visible through a telescope that has an appropriate resolving power
These can be difficult to detect if one of the stars’ brightness is much greater, in effect blotting out the second star
video

11. Astrometric binaries
systems in which only one star can be observed, and the other’s presence is inferred by the noticeable wobble of the first star
This wobble happens as a result of the smaller star’s slight gravitational influence on the larger star

12. Sirius A & B
In 1844 Friedrich Bessell pointed out that it had a wobble in its proper motion

13. Eclipsing binaries
In these systems, we are viewing the system edge-on (i90o)…
Stars eclipse each other during orbit
Just like exoplanets
Since inclination is now known, we can measure actual masses of the stars
From duration of eclipse, we can determine sizes of the stars
Thus, very important systems for underpinning our basic knowledge of stars

15. Spectrum Binaries
If the stars are too close together to be seen separately, it is possible to identify the object as a binary based on its spectrum.

16. Spectroscopic Binaries
If the Doppler shift of a star’s absorption lines changes with time (redshift, then blueshift, then redshift, etc.), it’s a spectroscopic binary.

17. Finding of mass
Astrophysicists find binary systems to be quite useful in determining the mass of the individual stars involved
When two objects orbit one another, their mass can be calculated very precisely by using Newton’s calculations for gravity
The data collected from binary stars allows astrophysicists to extrapolate the relative mass of similar single stars
video

18. Binary Stars - Types
Many are unknown as they simply have not been seen to vary (line of sight / observed)
Binary Stars are the fundamental way in which we understand stars (and star systems): their formation, evolution & death.
Remember --Three out of every two stars are in a binary system

19. Hint for tomorrow’s test!!
You need to know about:
Absolute Magnitude/Apparent Magnitude.
Luminosity/Temp/Size
What are they?
How do you calculate them?
Etc.

20. What are 5 specific things about stars you think will be on the test tomorrow?

21. To Review! Crash Course 26-36 (not 27)

22. I need to see your version of this before you take your test!

23. Last activity before your test