I was sick all last week and these notes were exactly what I needed to get caught up. Cheers!
Astro 113 Exam #2 Review
What details might we observed on the surface of a Gtype star?
Main sequence G stars have surface temperatures that range from 5250 5950 K and 66150 % of Sol’s luminosity. Gtype dwarf stars have between 0.851.1 Solar masses, which indicates in theory, that these stars spend 715 billion years in the main sequence fusing core hydrogen. They appear yellow. Spicules, sunspots, coronal mass injections, solar flare, plages, filaments.
Compare an Otype main sequence star with a Ktype main sequence star.
Class O very hot and very luminous, most of their radiated output is in the ultraviolet range. Most rare
Class K orangish, slightly cooler than the sun. Make up about 12% of main sequence stars, some are giants and super giants, some are main sequence stars. They have weak hydrogen lines (if present at all) and neutral metals (Mn I, Fe I, Si I) may be able to be a sun which would lead to more “Earth” like planets.
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What is the MassLuminosity relationship for main sequence stars and which are the most massive? The most luminous stars are the most massive, least luminous are the least massive.
Which main sequence stars are the bluest? O stars
The reddest? M stars
What is the approximate surface temperature of a G0 type star? 5,500 K
What are the elements and stages of premainsequence stellar evolution?
1. Begins with a cloud of cold gas which contracts under selfgravity(prostar). Potential energy is transformed into kinetic energy, which then is thermalized so the temperature goes up.(this phase last a short time) Don't forget about the age old question of What is the ratchet effect in macroeconomics?
2. When the cloud is hot enough the gas in ionized and opacity sets in (the gas finds it harder to lose energy and becomes hotter quicker)
3. The star moves in the HR diagram on the Hayashitracks, with constant temperature and decreasing luminosity. The convective zone recedes from the center and the star moves to higher effective temperatures. Slowly nuclear burning starts at the core
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4. Once nuclear burning has set in a star is born and appears on the main sequence. How are Type 1 Supernovae produced? Type II?
Type I: begins as white dwarf, the mass exceeds Chandrasekhar limit (see below) and it explodes. Hydrogen emission lines are absent which means there is little or no hydrogen in the debris from the explosion.
Type II: core collapses, gamma rays tear apart atoms, neutrinos can’t escape pressure, material falling into core bounces and blasts everything away, high temps and densities in the shock wave, radioactive decay creates other elements, extremely bright, outshines all other stars in galaxy for 200 billion years. If you want to learn more check out What do whales use sound for?
Where were the Carbon atoms in your pencil, the Nitrogen and Oxygen atoms you are breathing, and the Calcium atoms in your bones were all created?
Supernova, and Stardust.
What are the stages of evolution of very massive stars?
1. Hydrogen fusion
2. Helium fusion
3. Carbon fusion
4. Neon fusion
5. Oxygen fusion
6. Silicon fusion
7. Core collapse
8. Explosive supernova
What are the endstates of lowmass star evolution?
Lowmass stars consume all the hydrogen into its core, it ignites nuclear reactions that convert helium to carbon and oxygen. Process of mass ejection strips away stars outer layers and leaves the core open, allowing it to cool down like a dying ember (white dwarf)
Of highmass star evolution?
Highmass stars have high enough temps and pressure to further reactions, carbon fusion produces oxygen, neon, sodium, and magnesium. Neon fusion furthers oxygen and magnesium amount. Oxygen fusion produces silicon. Silicon fusion produces a sulfur, iron and nickel. High mass stars violently blow apart in Type II corecollapse supernova explosions.
What causes the luminosity of a star?
The size and matter of stars, the rate of release of energy increases stars luminosity. What is hydrostatic equilibrium?
A balance between the weight of a layer in a star and the pressure that supports it. Which stars evolve the most rapidly?
High mass stars. O stars
What condition keeps a white dwarf from collapsing further?
Kept from collapsing by the pressure of its degenerate electrons. Degenerate pressure doesn’t depend on temp so as the star cools it continues to hold the star together. We also discuss several other topics like What is Flocculating?
What defines a star on the main sequence?
A star that derives its energy from core hydrogen fusion. Luminosity and surface temp place it on the main sequence of the HR diagram.
Where are elements heavier than Iron created?
What is a pulsar?
A pulsating radio source that is associated with a rapidly rotating neutron star. What is a planetary nebula?
Luminous shell of gas ejected from an old, lowmass star.
What stellar property determines the final stages of a star’s life?
What is white dwarf?
Lowmass star that is don’t burning its thermonuclear fuel and is a size around the size of earth. How can we measure a star’s surface temperature?
Color ratio of a star
What do stars form from?
Cool and dense gas and dust in the ISM. Don't forget about the age old question of Geosphere means what?
Where is the energy of a main sequence star produced?
In its core through converting hydrogen to helium
Where does the energy come from?
How can we determine the age of a star cluster?
Presence of lack of luminous blue, highmass main sequence, without this sequence it shows that the main sequence in the cluster has been “eaten away”.
Type I and II Supernovae are produced in very different sorts of astronomical systems. If I observe one going off in a distant galaxy, how can I tell whether it is Type I or Type II?
Type II supernovae have hydrogen emission lines, Type I don’t.
What causes a nova?
Core collapse of a massive star, or explosion of a white dwarf star.
How do astronomers study prestellar object?
They give off radio waves so they can be detected using detectors that are sensitive to these electromagnetic radiation.
What is the maximum mass of a white dwarf?
Maximum mass of a white dwarf is called the Chandrasekhar limit, which is equal to 1.4 M What happens if it exceeds the mass limit?
How will the Sun evolve?
From the main sequence the sun will become a red giant, and then have a helium flash, start the 2nd red giant phase, increase by size of 100 times, envelop mercury and maybe Venus, then nuclear reactions will end it will become a white dwarf.
What is the heaviest element that can be produced within the core of a very massive star by fusion?
Iron it requires more energy that it produces.