2. PULSATING VARIABLE STARS Types of Intrinsic Variables:  Long-period variables  Cepheid variables  RR Lyrae variables  Flare stars Cepheid variables are type F to type K supergiants - yellow in color, pulsating stars, and relatively rare. Average Temperature = 4000 to 8000 Kelvin Average Luminosity = 300 to 40,000 L sun Cepheids and RR Lyrae

3. Some Information About Stars On the Main Sequence

4. Cepheid & RR Lyrae Variables

6. Distances Using Cepheid Variables These variable stars show intrinsic brightness variations.  Cephei

7. From the `light curve', you can tell that it is a Cepheid or RR Lyrae variable. RR Lyrae Cepheid The period is simple to measure, as is the apparent maximum brightness.

8. In addition to the standard Type I Cepheids, there is also a Type II Cepheids A complicating factor: There are two types of Cepheids. Classical

9. To find the distance to a Cepheid Variable: (2) Measure period of pulsation of the star. (3) Magnitude (Mv) from the Period. (1) Determine that the star is a Cepheid Variable (4) Measure the apparent magnitude m (5) Calculate the distance to the star using: m – M = 5 log(d)-5

10. Why are Cepheid variable stars important? The period of a cepheid variable is directly linked to its average brightness: the longer the period, the brighter the star. RR Lyrae Stars Similar to Cepheids, only smaller and fainter. Period = 4 hours to 1 day

11. Then we next start with AA to QZ and after that V followed by a number.An example is V335 Tau. There are over 2000 known variable stars in Sagittarius alone. The first variable star in a constellation is called R (e.g., R Orionus), the second S and so on through Z. After that, the next set uses double letters, beginning with RR, then RS, and on to RZ. Repeat to ZZ. Variable stars are named by constellation and in the order that they are identified.

12. Nebulae Dust and Gas form three Dark nebula (Dark) Emission (Bright) nebula (Red) Reflection nebula (Blue ) different types of nebulae

13. Reflection & Emission Nebula

14. Emission Nebula are Red HII Region and Recombination Hot stars illuminate a gas cloud and excites or ionizes the gas. Electrons get kicked into higher orbit, fall back to ground state, producing emission lines. Trifid Nebula

15. Emission Nebulae

16. Dark Nebula Example: Snake Nebula Contain gas and dust that block light Cool (10’s K) Larger than our Solar System

17. Reflection Nebula Gas and Dust Absorption line spectra (stars) Doesn’t generate own light Scatters blue light from starlight passing through Nebula appears blue (like sky) Witch Head Nebula Pleiades

18. A Panorama in Orion Can you ID the different types of nebula here?

19. Dark Nebula have lots of dense gas and dust. More opaque than others and blocks light. Hot Young Stars Always in the spiral arms Emission Nebula, gas is ionized by UV from stars. Electrons combine with ions, drop to lower orbits giving off visible light (red in color) Reflection Nebula (dust) Blue Types of Nebulae UV Visible light Dark Nebula Emission Nebula Reflection Nebulae

20. When we see a star through interstellar clouds, it appears redder than it actually is. This happens because short wavelength, mainly blue starlight, is scattered more by dust than longer wavelength red light. This interstellar reddening is different from reddening due to the doppler shift. Doppler shift causes all wavelengths to lengthen equally, while interstellar reddening does not change the wavelength of the star light, only their intensity.

21. Star Clusters

22. Open Star Clusters (Galactic Clusters) Star clusters are roughly classified on how “tight” they are. The stars within an open cluster are, typically spaced about 1 parsec apart. It is estimated that there are 20,000 open clusters within our galaxy. Open clusters lie in the central plane of our galaxy. where gas and dust are densest. “Open” clusters are less compact, and generally have a smaller numbers of stars (a few hundred ).

23. Globular Star Clusters  “Globular” clusters are more compact, and generally have relatively large numbers of stars (a few hundred thousand). Old stars some with ages of about 12 billion years. No new star formation is taking place. Stars are tightly bound and do not break apart like galactic clusters.

24. Clusters Two main types - Open Clusters and Globular Cluster Few hundred thousands stars 25 pc wide - densely packed! Old, cool stars Metal poor Found away from galactic disk Contain RR Lyrae, Type II Cepheids Open Clusters Few hundreds stars 30 pc wide Hot, young stars Metal rich Found in galactic disk Contain Type I Cepheids Globular Clusters (Galactic Clusters)

25. Stellar Populations Globular Clusters are nearly pure H & He with little or no metals. They are old stars called Population II (two old, poor) Open Clusters (Galactic Clusters), have metals and they are hot and young. They are formed from recycled material. Population I ( one, hot young)

26. Young clusters in our Galaxy are called open clusters due to their loose appearance. During the exchange of energy between the stars, some stars reach escape velocity from the proto-cluster and become runaway stars. The rest become gravitationally bound, meaning they will exist as collection orbiting each other forever.

27. are at roughly the same distance from us. Stars in a cluster Clusters are useful “laboratories'' for testing had the same initial chemical composition, our theories of star formation. have the same age

28. Cluster HR Diagrams: The most massive stars at the top of the main sequence evolve into red giants soon because they die faster. Therefore, the older the cluster, the fewer stars to be found at the top of the the main sequence, and an obvious grouping of red giants will be seen at the top right of the HR diagram. This effect, of an evolving HR diagram with age, becomes a powerful test of our stellar evolution models.

29. The first diagram is of a cluster which is only 1 million years old. Why, the hottest O star has already been converted to a red supergiant. The cool K & M stars have not yet settled down onto the main sequence, and have not yet ignited hydrogen fusion in their cores.

30. The next diagram is of a cluster which is 100 million years old. The main sequence lifetime of a 6 solar mass star is 100 million years, so stars with M = 6 M sun ( spectral type A ) are just turning off the main sequence. K,M stars getting closer to the Main Sequence

31. The final diagram is of a cluster which is 10 billion years old. The main sequence lifetime of a 1 solar mass star is 10 billion years, so stars with M = 1 M sun ( spectral type G) are just turning off the main main sequence B yr

32. Globular clusters all formed when the universe was young. Open clusters formed more recently, out of ``recycled'' material containing heavy elements. The youngest globular clusters are ~ 10 by old. The oldest globular clusters are ~ 16 by old. We can use the turning off the Main Sequence to determine the age of clusters.

33. Line of Sight Doppler Motion (Radial Motion) Proper Motion (Tangential Motion) (v t ). (v r ) v Actual Motion

34. Radial Velocity The radial velocity of a star is how fast it is moving directly towards or away from us. (Doppler Effect) Radial velocities are measured using the Doppler Shift of the star's spectrum: Star moving towards Earth: Blueshift Star moving away from Earth: Redshift Star moving across our line of sight: No Shift In all cases, the Radial Velocity is Independent of Distance. Earth

35. Each of these velocities forms the legs of a right triangle with the true space velocity (v) as the hypotenuse. We can then use the Pythagorean Theorem to derive the True Space Velocity (v):

37. Thank goodness, my brain is full