Clicker Stellar Evolution

Transcription

1 ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TA: Nicholas Nelson Lecture 14 Thur 24 Feb 2011 zeus.colorado.edu/astr1040-toomre toomre Stellar winds from hot star Today s Bizarre Events Helium flash goes off in shrinking degenerate core of red giant: horizontal branch star with He core burning Double shell burning (H and He) yields red supergiant (RG II), blows off planetary nebula What does electron degeneracy mean? Look at properties of white dwarfs as end of life cycle for low mass stars Observatory Night #4 tonight, Part B on spectroscopy; writeups due Tues March 1 from Part A observing Planet Finder help session in computer lab G-116 G today, 1pm-3pm, by Nick Nelson; overview later in lecture Read 17.3 Life as High-Mass Star and 17.4 Roles of Mass Exchange and 18.1 White Dwarfs Clicker Stellar Evolution Which is correct order for some stages of life in a low-mass star? A. A. protostar,, main-sequence star, red giant, planetary nebula, white dwarf B. protostar,, main-sequence star, red giant, supernova, neutron star C. main-sequence star, white dwarf, red giant, planetary nebula, protostar D. protostar,, main-sequence star, planetary nebula, red giant REMINDER Life track of solar-mass star MS Red Giant I Horiz Branch Red Giant II (or Supergiant) RG I MS RG II 2: Subgiant to Red Giant (first visit) MS subgiant red giant H burning in shell, makes much more energy Vast expansion, RG phase lasts ~ 500 MY Huge convective envelope REMINDER MS red giant Contracting core in red giant gradually becomes electron degenerate -- what does that mean? 1

2 REMINDER 3: Helium Flash Thermostat is missing in degenerate gas Could be more than exciting! He core burning -- removes electron degeneracy He core burning now with thermostat! horizontal branch star 4: Horizontal branch star He core burning, H shell burning Helium flash He fusion to C in core (horizontal branch) Short phase, lasts ~50 MY Triple-alpha fusion: 3 He C H-R R diagram of globular cluster Discussion: City of Stars : What does it tell us? Why is it useful? 5. Red Supergiant Double-shell burning of H and He Phase could be very short if He burning is erratic (unstable) -- then lasts only a few MY, and blows off outer shells 2

3 luminosity Sun in its far future ~5+ BY Life track in H-R R diagram of solar-mass star blow lovely shell? RG II Thermal pulses in red supergiant blow off outer shells radius Many meanders, but MS phase longest, red giant phase(s) ) shorter, finally white dwarf left to cool slowly white dwarf Red Giant I ZAMS protostar Brightness / Distance Clicker Q B. Leonardo and Guinevere are two stars that have the same apparent brightness. Leonardo has a larger parallax angle than Guinevere. Which star is more luminous? A. Leonardo B. Guinevere C. Cannot determine from data given Brightness / Distance Leonardo has a larger parallax angle -- thus he is closer to us They both have the same APPARENT brightness, but Leo is closer B. Guinevere must be more luminous B. Clicker Poll of Advice How do you take notes (or listen) during lectures? A. I get most of it by just listening B. I write down some notes, then go back to book to look things up C. I listen, take some notes, then get copies of lecture slides from course website D. I enjoy talking with my buddies, and they tell me later if I missed anything 6. Planetary Nebula Outer shells of red supergiant puffed off Great pictures! Naked white dwarf emerges 3

4 Discussion for Tues: Shapes of Planetary Nebulae Spirograph NGC 6751 Cat s s Eye Etched Hourglass NGC 7027 Ant Nebula Mz 3 4

5 Discussion for next Tues What is likely to account for the vast range of shapes (many beautiful) of these ejecta? Life after brief planetary nebula stage. Hot central core emerges as WHITE DWARF Ring Nebula 7. White Dwarf Inert C core, He & H shells Sizes of white dwarfs electron degeneracy pressure holds it up Very dense, size of Earth max mass of 1.4 M SUN More massive white dwarfs are SMALLER! Overview reminder: Life track of low-mass star Final stage: Cooling white dwarf --- snooze. But if WD has binary companion, much fun can begin! WHITE DWARF NEBULA MS RG I RG II 5

6 10 6 Luminosity (solar units) PLANET FINDER PROJECT Hunting for Extra-Solar Planets Direct Imaging, Transiting, Radial Velocities Tues consider evolution of massive stars after MS Doppler wobble of central star ,000 Temperature 2,000 Read Chap 13, Other Planetary Systems Radial velocity of 51 Pegasi Doppler wobbles of other stars 6