10 The H-R Diagram I bet my dwarf can beat your giant.

10 Goals Look at parts of H-R diagram. Lifetimes? Sizes? Clusters?

10

10 Main Sequence & Thermal Radiation The Main Sequence makes sense! Hotter stars are bluer. Hotter stars are brighter

10 The Main Sequence Stars characterized by what holds them up. 90% held up by heat of Hydrogen fusion 4H  He + Energy

10 M.S. Lifetime More Massive  Hotter Hotter  More luminous More luminous  shorter life

10 Clusters Groups of stars all at the same distance and age. Watch evolution along the H-R diagram. Get age of cluster.

10 Open Clusters These are the new stars. Small groups of young stars. Slowly drifting apart. Jewel Box – copyright MichaelBessell

10

10

10 Angular Size Linear size = how big something really is –Meters, inches, light years, feet Angular size = how big something looks –Degrees, arcminutes, arcseconds, milliarcseconds Circle = 360 degrees 1 degree = 60 arcmin 1 arcmin = 60 arcsec 1 arcsec = 1000 mas

10

10 Angular vs. Real Size Distance Diameter 

10 Stellar Radii How big are stars? We see stars have different luminosities and different temperatures. Stars have different sizes. If you know: –Distance –Angular size Learn real size. 50 mas

10 Angular versus Real Supergiants, Giants and Dwarfs

10 Betelgeuse Angular size = 50 mas Parallax = 7.6 mas = arcsec Apparent mag = 0.6 Distance = 1/parallax = 132 pc True size = distance * angular size = 1400 R sol Absolute Mag = m – 5log(d/10pc) = -5 –Our sun M ~5, Betelgeuse = 10,000x luminosity

10 Globular Cluster 12 billion years old

10 M13 M13 – Natalie Redfield ‘06

10 Luminous Giants Why are Red Giants more luminous than main sequence stars? –Hotter things are brighter per square inch. –The larger the star, the more square inches. –Luminosity is total light given off.

10 Concept Test Which star is: 1.Hottest? 2.Most luminous? 3.Least likely to be found in an open cluster? 4.Least likely to be found in a globular cluster? Of Main Seq. Stars? 1.Most massive? 2.Longest Life span? StarSpec Type mM AB0 V0.0 BG2 V CK5 III DF7 I-5.0 EK3 V5.06.5

10 Homework #10 For Oct 13: Reread B17.1 – B17.2, Do B16 Problem 20, and B17 Problem 1, 18