Sections
wavelength_max = about 3000 micron-K / 3000 K = 1 micron
and thus in the infrared.
HELIUM FLASHES happen only to stars in the 0.4--2 or 3 solar mass range (Se-251; FK-472).
The Sun from Main Sequence to the Horizontal Branch.
So the helium exhausts in the core and then there is an non-burning carbon-oxygen core, surrounded by a helium-burning shell surrounded by a hydrogen-burning shell.
Each THERMAL PULSE causes a superwind that blows off much of the the Sun's envelope.
The Sun from the 2nd red giant phase to white dwarfdom.
Planetary nebula atoms are excited by UV radiation from the remnant star---which is very hot on the surface---and emit copious LINE SPECTRA.
Green lines from doubly ionized oxygen are often particularly noticeable (Se-268).
PLANETARY NEBULAE have huge range of behavior---which we won't go into here, but we will show some pictures.
The Ring Nebula from HST. The best known of all planetaries.
The Ring Nebula is about 2000 lyr away in constellation Lyra. The ring is about 1 lyr in diameter. The green color is due to green forbidden lines of O III (i.e., twice ionized oxygen). The blue is from helium and the red color is from ionized nitrogen.
Credit: NASA: Imagine the Universe.
Planetary nebula Cat's Eye from HST.
The Cat's Eye is about 3000 lyr away in constellation Draco. It is one of the most complex of planetary nebula and is estimated to be only about 1000 years old. The green color is due to green forbidden lines of O III (i.e., twice ionized oxygen).
Credit: NASA: Imagine the Universe.
The PLANETARY NEBULAE disperse in the interstellar medium after a few thousands to tens of thousands of years.
After some thermal pulses, the remnant Sun will have lost most of its hydrogen and helium and perhaps about half its mass and shrunk to a size of order the size of the EARTH.
The time from becoming a 2nd red giant (AGB star) to being a WHITE DWARF is about 0.7 Myr (FK-493).
Stars that start out more massive than about 4 solar masses can burn carbon and oxygen (FK-497), but if they too end as white dwarfs if they arn't massive enough to become supernovae: i.e., have masses greater than about 8 solar masses.
But although the SOLAR WHITE DWARF will be mostly carbon and oxygen, the lighter helium and hydrogen atoms float on the top and form a skin.
WHITE DWARFS are not held up by ordinary gas and EMR pressure, but by a quantum mechanical pressure of degenerate electrons that is NOT very temperature dependent.
WHITE DWARFS are initially very hot with a surface temperature of order 30,000 to 100,000 K (Ni-178).
Initially, a WHITE DWARF'S EMR peaks in the UV and in the visible they appear white: hence the ``white'' in WHITE DWARF.
But they arn't very bright because of their small size.
But WHITE DWARFS have no energy sources.
They can only lose thermal energy and cool off forever.
Eventually they will drop to such low temperatures that they only radiate in the microwave or radio. They will then be called BLACK DWARFS.
But their cooling time is very long---many billions of years. Since the Big Bang, no WHITE DWARF has cooled off to become a BLACK DWARF it is thought.
The coldest existing WHITE DWARFS have surface temperatures of about 6000 K????.
Caveat: the post-main-sequence evolution of stars is fairly well understood in qualitatively from a combination of observations and theory.
But quantitative predictions are difficult. The three-dimensional hydrodynamic computations required test the limits of our modern computer codes.
We can only tell the best story we can given present understanding.
Well its a bit uncertain. It depends on how large Sun gets in its red giant phases.
If the Sun's radius is always less than 1 AU, the Earth might survive as a cold rock for many billions of years after the Sun becomes a white dwarf. It's orbit will have to change somehow as the Sun loses mass.
If the Sun exceeds 1 AU as some sources claim (Ze2002-344), then the Earth will be enveloped by the Sun.
Once inside the Sun's atmosphere, there will be drag force that will cause the Earth to spiral into deeper layers and there it will be evaporated. The time scale after envelopment is about 200 years (Ze2002-344).
`` So the glory of this world passes away: sic transit gloria mundi.''