Evolution of Low Mass Stars -- like the Sun < 2 – 3 Msun

1. Evolution of Low Mass Stars -- like the Sun < 2 – 3 Msun

2. Post Main Sequence Evolution -- the Red Giant Stage

3. The Sun as a red giant

4. Second Red Giant Stage -- the Asymptotic Giant Branch (AGB)

5. Post AGB, Planetary Nebulae and White Dwarfs -- final stage for the Sun

7. The Sizes and Masses of the stars – what do the large numbers mean? Measurement of Sizes and Masses Direct: Masses -- stars in binary systems Sizes -- binary systems -- interferometry, measure angular size, must know distance Indirect: -- must know distance Luminosity – depends on surface area (size) and temperature (Stefan-Boltzman Law) Mass -- with luminosity + physics , mass – luminosity relation

8. Sun, R = 7 x 105 km , > 100 x Earth

9. And putting the Sun in perspective with the size of other stars Sirius – visually brightest star, Arcturus – a red giant, one of oldest can see

10. Evolution of the Most Massive Stars -- >/= 10 Msun He-burning begins as a red supergiant, no electron degenerate core He -> C,O , C,O ->heavier elements up to Fe, as a red supergiant or successive transits across HR diagram

11. The Supergiants - - largest and most luminous for their temperatures Rigel ~ 150 x Sun, Betelgeuse ~ 600 x Sun

12. Research at Minnesota on Evolved Massive Stars The evidence for episodic high mass loss events

13. One of the Largest -- The Extreme Red Supergiant VY CMa 10 arcsec Distance -- ~ 1.5 kpc Luminosity ~ 500,000 L sun Initial Mass ~ 30 -- 40 M sun Temperature ~ 3500 K Size ~ 2000 Rsun, ~ 10 A.U. (Saturn’s orbit!) 1” = 1500 AU

14. What does it mean to say a star is as big as Saturn’s orbit? Betelgeuse 600 x Sun = 3 A.U. Earth – Sun distance 150 x 106 km 1 astronomical unit A.U. VY CMa 2000 Rsun = 10 A.U. = Saturn’s orbit

15. Complex structure in ejecta Prominent arcs, numerous filaments and clumps of knots, strong maser source, mass loss rate 5 x 10-4 Second epoch HST images Measure transverse velocities combined with radial velocities (VR) long slit spectra (Keck) using the Doppler effect NW Arc Arc 2 Arc 1 S Knots SW Knots

16. 2nd Epoch images with HST/WFPC2 Measured the transverse motions VT - shift in x and y positions between the two images. 66 positions -- pushed the limits of HST ~ 0.02 arcsec Combining VT + VR --> VTot Total velocity relative to star Orientation Direction of motion Age or time since ejected

17. The 3D Morphology of VY CMa Feature Vel. Orientation Direction Age (yrs) km/s relative to sky of motion NW arc 46 22 degrees ~ west 500 Arc 1 68 -33 SW 800 Arc 2 64 -17 ~ south 460 SW knots 36 -25 ~ west 250 S knots 42 -27 SSE 157 SE loop 65 -21 SE 320 Discrete structures, -- arcs, knots, filaments – ejected at different times, from different regions on star -- localized Large-scale convective activity  Starspots  Magnetic Fields

18. Comparison with the Sun -- prominences, sunspots and coronal mass ejections: Solar wind VY CMa 109 kg/sec 2 x 1019 kg/sec CME discrete ejecta 1010 kg/sec ~ 1020 kg/sec

19. The (brightest) Most Luminous and Most Massive Star known – (in our region of the Milky Way galaxy) Eta Carinae -- in the southern hemisphere

20. h Car : Distance -- 2.3 kpc Luminosity -- 5 x 106 Lsun Initial Mass ~ 150 – 200 Msun Temperature ~ 20,000 K Size ~ 0.4 A.U ( Mercury’s orbit) h Car and the Homunculus Nebula

21. Historical light curve Great Eruption – 1837 – 1858 Reached 3 x 107Lsun Expelled ~ 20Msun, 1 Msun/yr Total luminous energy ~ 1050 ergs