ASTR 1120: & Today’s Stellar Events • Look at supergiants, planetary nebulae and white dwarfs formed at end of evolution of low- mass stars • To come in next lecture: Evolution of massive stars through giant and supergiant phases: fusion occurs in `successive layers of onion’ • End life as supernova explosion, leaving behind Crab either neutron or black hole -- Supernova • Observatory Night 5 tonight – by sign-up Remnant • “Overview of stellar evolution” summary still available + new Homework Set # 6 (due Mon) Prof. Juri Toomre TA: Ben Brown / Licia Ray • Read 18.2 white dwarfs & 18.3 neutron stars Lecture 21 Mon 28 Feb 05 zeus.colorado.edu/astr1120-toomre

Clicker Poll of Advice Clicker break – what has stuck? • How do you take notes (or listen) during lectures? • The vast majority of stars in a newly formed star cluster are ______? • A. I get most of it by just listening • B. I write down some notes, then go back to A. book to look things up • A. less massive than the Sun • C. I listen, some notes, then get copies of • C. I listen, some notes, then get copies of • B. very high-mass, type O and B stars lecture slides from course website • D. I enjoy talking with my buddies, and they tell • C. red giants me later if I missed anything • D. about the same mass as Sun

Reminder of evolution stages: PN Star Birth Protostar Æ RG II Cauldron MS Æ Red Giant I Æ Horiz Branch Æ WD Red Supergiant RG I blows off NGC 604 in M33 MS Triangulum

1 REMINDER Helium flash Æ 4: Horizontal He fusion to C branch star in core (horizontal branch) He core burning, H shell burning

Short phase, lasts ~50 MY

Triple-alpha fusion: 3 He Æ C

5. Red Supergiant 6. Planetary Nebula Double-shell burning of Outer shells H and He of red supergiant “puffed off” Phase could be very short if He Great pictures ! burning is erratic (unstable) -- then lasts only “Naked” a few MY, and white dwarf blows off outer emerges shells

Sun in its “far future” ~5+ BY

Thermal pulses in red supergiant blow Ring off outer shells Ring Nebula

2 NGC 7027 NGC 6751

Ant Nebula Mz 3 Ant Nebula Mz 3 Spirograph

Cat’s Eye NGC 3132

3 Planetary nebulae Overview revisited: Life track of low-mass star in many shapes: rotation and magnetic fields ?

Squid

NGC 6369 Stingray

7. White Life after brief Dwarf “planetary nebula” Inert C core, stage …. He & H shells Hot central core electron degeneracy emerges as pressure holds it up

WHITE DWARF Very dense, size of Earth

max mass of Ring Nebula 1.4 MSUN

Clicker -- Paths in H-R Diagram Final stage: NEBULA • A star moves upwards and to the right on the Cooling RG II H-R diagram. What is probably happening in white dwarf the core? --- snooze …. B.

WHITE A. The core has just started to burn a new But if WD has DWARF RG I element binary B. The inner core is collapsing and heating up; companion, shell burning is increasing much fun can MS begin ! C. All nuclear burning is slowing down D. The inner core temperature is cooling

4 HR diagram shifts Overview revisited: Life track of low-mass star

•B. The core is collapsing and heating; shell burning is increasing

• Moving upwards on HR diagram means more luminosity Æ more nuclear fusion • This is usually due to the inner core heating due to gravitational collapse potential Æ thermal Æ faster burning

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