1. Not going to the observatory tonight. Tonight will be time for Lab 3.
Sept. 30, 7:30-10:30pm, open house at Baker Observatory. If you can help, please contact
Dr. Patterson
Lab 1 is now late.
After today, Lab 2 will be considered late.

2. O Stars: HeII, HeI, H lines B Stars: HeI and H lines
Spectral Types
O Stars: HeII, HeI, H lines
B Stars: HeI and H lines
A Stars: H (strongest), CaII, FeII
F Stars: H (weak), CaII, ionized metals.
G Stars:H (weaker), CaII, neutral and ionized metals.
K Stars: CaII (strongest), neutral metals (strong).
M Stars: Neutral elements, molecules (TiO)

3. Luminosity class: Roman numerals: I – VI
I = supergiants, III = (red) giants
V = main sequence
This is really pressure broadening where higher g = higher p = wider lines.

4. And temperature relates to color!

5. HR diagrams.
A long time ago, two guys, Hertzsprung and Russell showed stars with known distances, and so absolute magnitudes compared to their color through 2 filters. This became known as the HR diagram.

6. Because these are measurable from imaging.
It has many variants, the most popular of which are color-magnitude diagrams (CMD).
Because these are measurable from imaging.

7. Color-Color diagrams

8. Research these on your own.
Stars on an HR diagram fall into regions; typically the Main Sequence, Red Giant Branch, Horizontal Branch, Supergiants, and White Dwarfs.
Research these on your own.

9. Ground-based observations look through atmosphere

10. Atmospheric Extinction
The more atmosphere that is between us and our target, the more extinction occurs. This is called atmospheric extinction. Our goal is to approximate observations as if they were above the atmosphere.

11. Atmospheric Extinction
In this case, Z is the zenith distance (angle).
This allows us to define airmass, which is the amount of atmosphere between you and your object.
Airmass = X = 1/cos(Z) = sec(Z)

12. Atmospheric Extinction
mo is the magnitude above the Earth’s atmosphere, which is what we want.
Airmass = X = 1/cos(Z) = sec(Z)
Then extinction looks like the equations above.
Where c and k are constants.

13. If we plot apparent magnitude against airmass, the slope is a (mostly) linear relationship, and is the constant k. We can then find the y-intercept and that is the magnitude above the Earth's atmosphere.

14. In practice, it is tougher
In practice, it is tougher. Here are actual measurements for 1 star observed over several hours during 1 night.

15. Atmospheric Extinction
Unfortunately, extinction is wavelength dependent. It is also location and time dependent!
So it has to be determined every night!
And a constant, k, for every filter.

16. Atmospheric Extinction
Typical values for the Johnson-Cousins U,B,V,R,I, system:
Filter k U B V R I

17. Atmospheric refraction.
The atmosphere also refracts (bends) light. Which of course changes with more atmosphere.

18. Atmospheric dispersion.
This is also wavelength dependent. So at larger airmass, blue light with move more than red light.
Important for spectroscopy (many-lensed systems)

19. Through a small telescope, the stars will all dance together.
The atmosphere really consists of many cells, which all move around. This is typically called 'seeing'- the star appears to dance around.
Through a small telescope, the stars will all dance together.

20. But through a large telescope, the mirror sees light through several different atmospheric cells (~1m in size) and the stars do not move in unison.

21. Seeing is mostly what the radial profiles in IRAF are measuring
Seeing is mostly what the radial profiles in IRAF are measuring. Therefore, the FWHM is mostly seeing.

22. Through the atmosphere Not through the atmosphere

23. There are ways around this, if all you're after is image quality.
One way is to 'stack' images.
1) You take a lot of images, 2) discard the blurry ones, 3) shift the clear ones to a common center and 4) combine them.

24. There are some pretty good (and free) software packages to do this for you: Registax, AstroStack, K3 CCD Tools are three of them.

25. Processed using Registax
Images taken during 1 night using a 12.5” Ritchey-Chretien telescope and a Philips ToUCam Pro webcam.
Each image is 640x480 at 10fps.
1200 frames taken, 340 used.
Processed using Registax
And Photoshop.

26. Telescopes!

27. Telescopes * Telescopes perform key functions:
- Collect light (EM radiation) from astronomical sources.
- Record information on that light:
- Position
- Arrival time
- Energy
* Different telescopes and detector combinations measure some or all of this information (and can be optimized for specific wavelengths/energies).

28. Positional information -structure of galaxies -motions of stars (distances)

29. Energy information: A spectrum (or color information using multiple filters).
We get compositions.

30. If we use time information, we get a lightcurve.
- Study transits (exoplanets)
- Binary stars (masses & distances)
- Asteroseismology (everything!)

31. What we wish to know dictates the telescope/instrument used
Positional information -structure of galaxies -motions of stars (distances)
Energy information: A spectrum (or color information using multiple filters).
- Composition
If we use time information, we get a lightcurve.
- Study transits (exoplanets)
- Binary stars (masses & distances)
- Asteroseismology (everything!)