Astronomy 2022 November 7-9

low mass (lower main sequence, .5-8 M, planetary nebula/ CNO white dwarf), intermediate mass (upper main sequence, 8-10 M, planetary nebula/O-Ne-Mg white dwarf), high mass (upper main sequence, 10-25 M, supernova/neutron star)

mostly young, hot, blue stars in small populations in spiral arms

mostly old, cool red stars in large populations in the halo

can e used to estimate cluster ages. Where main sequence stars turn off the main sequence and move towards giant stars. As cluster ages, stars at this point are lower mass. Color is an indicator

main sequence, red giant, horizontal branch, asymptotic giant branch, planetary nebula, white dwarf

hydrogen-helium core fusion with hydrostatic and thermal equilibrium

change any of the 3 main sequence conditions and the star will leave

helium ash builds up in core and hydrogen fusion is pushed out into shell surrounding core. Loses hydrogen core fusion. Helium core begins collapsing and heating with KH, loses hydrostatic equilibrium.
heat of shell fusion and KH heating increases energy. Loses thermal equilibrium. Heat pressure pushes envelope out

helium ash cores with KH heating, hydrogen shell fusion, hydrostatic and thermal equilibrum out. Brighter with higher surface area but cooler

takes a 1M star about 1Gyr to climb to top. Helium core continues to collapse and heat, no fusion. Shell fusion continues. Core temperature reaches 100m K at top

helium flash. At 100m K, helium core fusion begins (triple alpha process). Now core is building carbon, nitrogen, and oxygen ash. Nitrogen formed in CNO bi cycle. Star leaves red branch

hotter, bluer, smaller, less bright than red giants. Re establishes hydrostatic and thermal equilibrium, shrinks in radius. Helium core fusion, hydrogen shell fusion, hot blue hydrogen envelope.

lasts for 100 Myr, CNO ash builds but core is too cool to ignite carbon fusion. Three helium nuclei fused into one carbon nucleus, second reaction creates oxygen from carbon and helium.

after 100 Myr CNO ash builds up and the helium fusion pushed out of core into helium shell

hydrogen and helium shell fusion. envelope grows in radius, cools and reddens. Climbs branch and has a higher temperature and luminosity. Inert CNO cores with KH heating. Out of hydrostatic/thermal

temperature sensitivities, small temperature changes in helium fusion results in thermal pulses. Envelope disconnects from core and drifts away, expanding envelope forms planetary nebula around CNO core

different types of fusion have different kinds. As you raise the temperature of fusions area, increase rate of fusion. Hydrogen fusion= a 1% temperature increase results in 4% fusion increase
Helium fusion= 1% temp increase results in 40% fusion increase

occurs once every 10k years, continues 100k years. Drives envelope away from core and results in mass loss.

expanding envelope around CNO core, nebula ionized by central core, glows different colors for different elements. Will expand and disappear in 10k years

CNO core exposed. Temperature and luminosity decreases, will move to this region. remaining core small and hot. Low mass stars

1a: brightest supergiants
1b: less luminous supergiants
2: bright giants
3: giants
4: subgiants (intermediate)
5: main sequence dwarfs (M-S)
D: white dwarfs

fuse hydrogen into helium during CNO cycle. In hydrostatic and thermal equilibrium. energy generation is balanced by luminosity

hydrogen core exhaustion after 10 million years. Lumiosity 10,000 L, life expectancy 10 million years.

helium ash builds in core, hydrogen core fusion lost and pushed out into shell surrounding core. Helium core collapses, heats w/ KH, loses equilibrium. Combined heat of hydrogen shell fusion and KH increases total energy. Heat pressure pushes envelope

moves horizontally across HR diagram, rare. Surface temperature drops, luminosity remains steady, inert helium cores with KH heating. Hydrogen shell fusion, cool, red hydrogen envelope.

core reaches 170 K, helium core fusion begins triple alpha process. Three helium nuclei fused into one carbon nucleus.

after helium flash, helium fusion in core and hydrogen shell fusion. In equilibrium

ends after 1 Myr. CNO ash core collapses and heats, helium fusion pushed out into shell, hydrogen fusion farther out. Star devolves into red supergiant. Takes 1000 years

only lasts 1k years. Carbon+Helium to Oxygen
Oxygen+helium to neon
Carbon+carbon to Magnesium
Eventually O, Ne, Mg ash fills core and carbon fusion pushed out into shell

8-10 M, carbon fusion network creates flow of neutrinos and thermal pulsation that destabilizes envelope. Envelope expands, disconnects and drifts away as planetary nebula, collapses as O-Ne-Mg white dwarf

greater than 10M. Stars want to maintain hydrostatic and thermal equilibrium, following fusion networks creates huge neutrino flow and energy loss. In order to compensate for energy loss and maintain equilibrium, fusion rates must accelerate

O-Ne-Mg ash core collapses and heats to 1.5 billion K, density 10 million g/cm^3. Fusion begins, creates magnesium, oxygen etc. In 10 years it’s no longer possible. o-Mg ash builds up in core, neon fusion pushes out into shell

O-Mg core collapses, heats to 2.1 billion K, density 10s of millions g/cm^3. Fusion begins and builds heavy silicon core with sulfur, phosphorous, etc. After a year it’s no longer possible. Si ash builds, oxygen fusion pushed into shell

core collapses and heats to 3.5 billion K, density 100 million g/cm^3. Fusion begins, creates iron, nickel etc. Lasts for a day. Silicon nuclei don’t fuse, melts into soup of helium nuclei, protons and neutrons. Other nuclei join

Fe-Ni core, Si burning shell, O burning shell, Ne burning shell, C burning shell, He burning shell, H burning shell

fusion of elements lighter than iron produces nuclei lighter than input elements, results in nuclear binding energy. Fusion of iron and heavier elements produces nucleus heavier than input elements. to make up for rate mass increase, energy is pulled from the system. As Iron builds up, all fusio non stops.

if the iron core exceeds 1.2-2M, gravity takes over and core collapses. Disastrous final collapse

Hydrogen burning 10 Myr
Helium burning 1 Myr
Carbon burning 1000 years
Neon burning 10 years
Oxygen burning 1 year
Silicon burning 1 day