Hertzsprung Russell (HR) Diagram

Spectral Types: Proxy for Teff

Or surface temperature

Our Sun: 5,700 deg Kelvin

Or about 10,000 F

O B A F G K M L T

Not to scale: Red Giant 100 times bigger than Main Sequence Star

Pre main sequence evolution:

1) Protostellar, self-gravitating Gas cloud collapses Then contracts in Hydrostatic equilibrium

2) Develops hot radiative core

3) Reaches ignition point for Hydrogen burning

Virial theorem: as cloud shrinksGravitational energy is releasedHalf of it goes into heating the interiorHalf of it is radiated away as luminosity(and its more luminous than it will beWhen hydrogen is burning)

3) Start of main sequence (hydrogen burning)

4) End of main sequence (core is now all helium)

5) Climbing giant branch hydrogen burning in shell around inert helium core hydrogen envelope swells up

6) Helium ignition in a “flash”

7) Helium burning to carbon/oxygen

7) Second climb upGiant brach: H- and He-shell burningAround inert C/O core(the pre white dwarf)

8) Ejection of Planetary Nebula exposes coreWhich contracts and Gets very hot as Upper layers peeled offEnters white dwarf phaseNear 100,000 deg Kelvin

9) White dwarf phase:Just cooling off and Getting dimmer

The Ring Nebula in Lyra

The pre-white dwarf is the very blue star at the center !

A Planetary Nebula

Star ejects envelopeof unburnt hydrogen

Many cool pics On Hubble web site

Sirius AB -- a Visual Binary 60 arcseconds = 1 arcminute = 1/60 of a degree

The Globular ClusterMessier 5

Stages of Stellar Evolution:

A) Core hydrogen burning = main sequence H > Hewhen finished: helium core

B) Red giant branch= hydrogen burning in shell around helium core

C) Tip of giant branch = ignite helium core D) Core burns He > C, O

E) He shell burning ejection of planetary nebula

F) Becomes white dwarf

Open / Galactic Star Cluster NGC6791 -- 8 Billion Years, 2-3 x solar metals

Isochrones for7, 8, 9 Gyr

Massive star evolution(> 8-10 M)

After helium burning To C,O

C ignites to O, Ne, MgIgnites to Si, S

Si, S to Fe peak elements(Ni, Ti, lots of Fe)

Now stellar core can do no more burningto produce energy

So it collapses and Explodes as a Supernova

Remnant core:Neutron Star or Black Hole

The Crab Nebula

Pulsar inside!

Pulses every 1/30 second

Supernova in 1054 A.D.

Recorded by the Chinese

Pulsar:

Rotating, Highly magneticNeutron star

Like a rapidly spinningSearchlight beam!

An X-ray pulsar (also optical, radio)

Jocelyn Bell Burnell

British radio astronomerGraduate student in 60s

Discovered first pulsars In radio signals With advisor Anthony Hewish

Sir Anthony Hewish Nobel prize in physics1974 for pulsars

• Impostors: contamination by other small stellar and substellar objects: the radii of small stars, brown dwarfs and giant planets are similar

S M T HJ J

Problems

Sol Gliese 229 Gliese 229b HD209458 Jupiter

T=5800K T~3400K T~ 950K T~1000K T~200K

M=1000 Mj M~300 Mj M~50 Mj M~1 Mj M=1 Mj

R=10 Rj R~3 Rj R~1 Rj R~1.4 Rj R=1 Rj

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Burrows and Liebert 1993 Reviews of Modern Physics

• OGLE planets have shorter periods than RV planets.

• Transit searches find a different population because the selection effects are different.

A new class of planets

Fig. From the California-Carnegie team