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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 105 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 Research at Minnesota on Evolved Massive Stars The evidence for episodic high mass loss events 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 What does it mean to say a star is as big as Saturn’s orbit? Earth – Sun distance Betelgeuse 600 x Sun 150 x 106 km = 3 A.U. 1 astronomical unit A.U. VY CMa 2000 Rsun = 10 A.U. = Saturn’s orbit Complex structure in ejecta Second epoch HST images Prominent arcs, numerous filaments and Measure transverse velocities combined clumps of knots, strong maser source, mass with radial velocities (VR) long slit spectra (Keck) using the Doppler effect loss rate 5 x 10-4 NW Arc Arc 2 Arc 1 S Knots SW Knots 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 The 3D Morphology of VY CMa Feature NW arc Arc 1 Vel. Orientation km/s relative to sky 46 22 degrees 68 -33 Arc 2 SW knots S knots SE loop 64 36 42 65 -17 -25 -27 -21 Direction Age (yrs) of motion ~ west 500 SW 800 ~ south ~ west SSE SE 460 250 157 320 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 109 kg/sec CME VY CMa 2 x 1019 kg/sec discrete ejecta 1010 kg/sec ~ 1020 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 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 Historical light curve Great Eruption – 1837 – 1858 Reached 3 x 107 Lsun Expelled ~ 20Msun, 1 Msun/yr Total luminous energy ~ 1050 ergs