ASTR 1102 Lecture : Lecture21
Document Summary
Burning hydrogen shell around the helium core. Massive agb stars dredge up so much carbon they are called carbon stars. All life as we know it is carbon-based. Helium carbon in triple alpha process. Brought to surface of agb star by dredge-up (convection) Most carbon in galaxy originates this way. Microwave image of carbon monoxide around carbon star. Repeatedly exhaust helium layer, then replenish it from hydrogen burning. Each time helium re-ignites it is a mini-helium flash. Unlike earlier helium flash, this does increase luminosity. Each pulse drives off some of envelope. Eventually only tiny (earth sized) hot (100,000k) core is left, surrounded by planetary nebula . Thermal pressure drops and core contracts white dwarf. Don"t confuse with red dwarf or brown dwarf. Agb phase it will orbit a white dwarf. Dim blue star gradually fading to yellow, then red. Like the sun as seen from pluto. Planetary nebula - the partial victory of pressure.
