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

Post Main Sequence Evolution -- the Red Giant Stage

The Sun as a red giant

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

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

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

Sun, R = 7 x 10 5 km, > 100 x Earth

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

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

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

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

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

What does it mean to say a star is as big as Saturn’s orbit? Earth – Sun distance 150 x 10 6 km 1 astronomical unit A.U. Betelgeuse 600 x Sun = 3 A.U. VY CMa 2000 Rsun = 10 A.U. = Saturn’s orbit

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

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

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

Comparison with the Sun -- prominences, sunspots and coronal mass ejections: Solar wind VY CMa 10 9 kg/sec 2 x kg/sec CME discrete ejecta kg/sec ~ kg/sec

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

 Car : Distance kpc Luminosity -- 5 x 10 6 Lsun Initial Mass ~ 150 – 200 Msun Temperature ~ 20,000 K Size ~ 0.4 A.U ( Mercury’s orbit)  Car and the Homunculus Nebula

Historical light curve Great Eruption – 1837 – 1858 Reached 3 x 10 7 L sun Expelled ~ 20M sun, 1 M sun /yr Total luminous energy ~ ergs