The perfect vacuum!!

 That's correct - if you asked those physicists who are working with vacuum equipment everyday. The best vacuum they achieve, is probably about a billion particles per cubic inch (as compared to a quadrillion particles in normal air). Good enough for them - but see how good the vacuum is aboard the Space Shuttle (and why they want to participate): ...

 ... the astrophysicist is working with (actually s/he merely observes it): between 0.00001 and 10,000 particles per cubic inch!  Not a perfect, absolutely empty vacuum, but certainly the envy of these experimental physicists.
 

A millionth of the amount of the best vacuum on Earth - hardly any particles around. And that should matter?

 Why should it matter? Let's forget about it.

 However, space is huuuuuuuuuuuuuuuuuuuuuuuge: Although the density is low, the volume is huge, and therefore the mass it constitutes of is large as well.

 So, it does matter.

What is it?

... 
North America Nebula (bright Deneb is at right) .

Gas and Dust.
Hydrogen, some Helium, and aggregates of molecules composed of metals (dust).
 

 There are gas clouds that absorb light (Hydrogen lines) from stars (Arny p.451ff; Ch/Mc p.307; Pasa p.502). 
The Eagle nebula in Serpens, stars are born here, (c) AURA / STScI .    There are emission nebulae, heated by a near-by young star, hot enough to produce an emission spectrum. And there are dark dust clouds, virtually absorbing all radiation. That's why we can't see the center of our Milky Way Galaxy (Arny p.453; Ch/Mc p.404; Pasa p.505).

 What are they important for?

 Once upon a time ... there was nothing in the universe but gas and dust - no stars. Then - all the sudden? - stars appeared. How come?

 Back up: stars consist of Hydrogen and Helium. Notice something?

The Trapezium in the Orion Nebula, another region of starbirth, (c) AURA / STScI .    The interstellar medium consists of Hydrogen and Helium as well.

It is the birthplace for stars!!

A gas cloud is the beginning of a star's evolution.

 That's correct.

 Does a gas cloud have enough mass to form a star? In fact, it needs a mass equivalent to 1,000 to 10,000 sun masses. Such a cloud has a radius of about 100 light-years.

A larger view of the Orion Nebula, (c) Martin Reble and Sebastian Kupijai., 8" Cassegrain, 5 minutes, 2-24-03. What is the main difference between a star and the gas cloud? Think about our discussion above and the star's density. ________________

 That's correct, too.

 How does a low density cloud become a high density star? ____________________

 That's correct, tootoo.

Well, how and why can it contract? Well, look at the above, a star's main condition of equilibrium: Most gas clouds are in hydrostatic equilibrium as well. Such a cloud would neither contract nor expand, therefore never form stars (Ch/Mc p.310f).

But, there are some clouds that are either massive enough or were triggered (e.g. by an exploding star - a supernova) to contract.
Giant Starbirth Region In Neighboring Galaxy, (c) AURA / STScI .

For these clouds, main condition of equilibrium is not fulfilled. ______________ is larger than ___________ and the cloud starts contracting.
Contract, contract, kontrahier, contract, fragment - oops, lots of small contracting clouds.

Proplyds in Orion Nebula, (c) AURA / STScI . Pump in the gas (e.g. with a bicycle pump - fast - and feel the nozzle: it's hot). So the temperature increases, and thus the pressure. But for a long time to come (formation of a protostar from a gas cloud takes between 1 million and 1 billion years) it won't be hot enough to match gravity.

(See Arny p.387; Ch/Mc p.312): the evolution of a solar mass star is discussed - yet, as (Arny Fig. 13.2&3, 13.17&21; Ch/Mc p.315; Pasa p.433) shows, stars of different mass follow the same pattern, although mass (of course) , temperature, luminosity, and time in labor are different.

 Eventually a protostar forms, with a definite radius and surface temperature, appearing on the HR-diagram. Look at the luminosity equation in (Arny p.359; Ch/Mc p.281). Although the protostar's surface is ½ as cold as our Sun's, it's radius is 50 times larger: therefore it is much ______________ than our Sun.

 Its core is at 1,000,000 Kelvin, still a factor 15 short of igniting nuclear fusion. So where does the energy come from that it radiates?

 "The grandest generalization of physics is the conservation of energy."
Physicists tell us that potential energy decreases as the cloud contracts. This energy must go somewhere: half of it is radiated into space, the other half continues to heat up the protostar.

 By the way, the cloud is still contracting. Still, gravity is stronger than pressure.
More by the way. I'm in Chadron, typing busily, with several people chatting, and so it's hard to be in a funny mood.

The Pleiades in Taurus, a young open cluster, (c) David Malin, AAO .  Contract, heat up, contract, heat up, contract, heat up, ignite Hydrogen, increase pressure, balance gravity. The main condition is fulfilled and

Inside Red Dwarfs (Gl752b), (c) AURA / STScI . At this stage the star will produce as much energy as it radiates into space. Here, on the Main Sequence, it will stay for billions of years (depending on its mass).

 How long did it take this new star to form from a gas cloud (check the Appendix )?

 Main sequence:

 M-stars 0.1 sun masses __________ years

 G-stars 1 sun mass __________ years

 O-stars 20 sun masses __________ years

 So, the more massive a star is, the _______________ it takes it to reach the main sequence.
Why? Because it's more massive and therefore gravity is larger, and therefore it contracts faster.

 The opposite of course is true for low massive stars.
 

(c) AURA / STScI .  What is the lowest mass for a star? _______ sun masses. ->  eventually gravity and pressure are balanced, but the core temperature is too small to ignite Hydrogen. It can still give off heat though, just as our 2 biggest planets do - hundred fold Jupiter's mass and it would have become a star. Such failed stars are called brown dwarfs (the first image shows Gliese 229B, the second Brown Dwarf Gliese 229B) , (c) AURA / STScI .

 What is the highest mass for a star? _________ sun masses. -> eventually such a massive star would have become hot enough to drive away the surrounding mass atop its surface, so it won't accumulate any more mass.
 

Summary:
Stars are forming from a contracting gas cloud.
The gas cloud must have sufficient mass (> 1,000 sun masses) or be triggered by an external event.
The cloud continues to contract and to heat up until it finally settles to be a star, which means that Hydrogen fusion has ignited (15,000,000 Kelvin) and gravity and pressure balance each other.
There it'll stay on the main sequence.

HR-diagram of the nearest stars, (c) Hipparcos, ESA . Well, it's not much evolving. It's like watching a light bulb for 5 months that steadily glows.  Eventually the tungsten will rip apart, the light bulb darkens. It would be exiting if the bulb would then implode.  However, for 10 billion years (we're at half time, so get a hot dog) the sun steadily burns hydrogen, its core depletes hydrogen slightly and increases its Helium amount. Due to this slow depletion the sun becomes slightly hotter and brighter. However, changes are far from being dramatic: At the end only 10% of its original hydrogen is used up and it is maybe 50% brighter (check Snow) (Snow's Universe is temporarily offline) .  The main sequence is by far the longest period in a star's life and by far the least eventful.  What is the lifetime of a star ( Appendix )?

Inside the core of a low mass star.  Energy is generated via the proton-proton chain.  (c) Redshift 3. Main sequence: M-stars 0.1 sun masses __________ years G-stars 1 sun mass __________ years O,B-stars 10-20 sun masses __________ years Has any M-star died yet? ... How many generations of O and B stars have already existed? ...

(see Arny p.396) Vogt-Russell Theorem: "The entire evolution of a star" depends solely on "its initial mass and chemical composition."

 Let's care about low-mass stars first (below 5 to 10 sun masses, including our own sun of course; the following development is the same for all low mass stars, just the amount of time it takes would differ according to their mass).

 Nuclear fusion in the core depends on temperature, pressure and density. Hydrogen fuses into Helium, which is four times as massive as Hydrogen. Therefore, Helium sinks to the center. This center keeps growing during a star's life.
At the end of its life, too little Hydrogen is left at the center where it would be hot enough for nuclear fusion -> the chance of Hydrogen nuclei colliding with each other becomes too small to keep fusion going.

 The hydrogen outside the Helium core is too cold though for fusion.

 The star loses its balance. Now that nuclear fusion ceased, what happens ...?

 ...

 That's right! You're fantastic.

 The contraction of the star releases gravitational energy, which radiates away into space. The star's surface temperature decreases (to about 3000 K, so its color is _______), but it also grows slightly, which causes its brightness to remain about the same. -> horizontal line in the HR-diagram.
This whole process, and including the next paragraphs of hydrogen shell burning, lasts about 100 million years (remember, no fusion during most of that time).

 During that time the Helium core shrinks and heats up, yet not enough to ignite Helium (due to its larger mass and two-fold electric charge it needs 100 mill. K). However, a shell of hydrogen around the core reaches its sufficient 10 mill. K and ignites -> Hydrogen shell burning.

 And nuclear fusion returns to the dying star, one of its last breaths. More eventful ones (last breaths) will follow.

 The heat from the hydrogen shell increases the size of the star hundred fold, also increasing its brightness dramatically (its surface temperature decreases slightly).

Betelgeuse, the only star (other than our Sun) for which it's possible to image its surface - because it's so big (size of Earth's orbit) and close enough, (c) AURA / STScI .   The star is cold (red) and huge (gigantic): A
 
 

More about that next time ...

... stay tuned to read about the Helium Flash, Carbon core (you don't wanna mine that diamond), Planetary Nebula, and White Dwarf.

 Now comes one of the hardest part, but judge yourself. It's about electron degeneracy.

 The balancing force against gravity is pressure. So far we have said that pressure depends on temperature, applying unconsciously the ideal gas law (pressure ~ temperature). But now that the core is contracting even further, this doesn't hold any more.

 How do atoms look like inside a star's core? ____________________________________

 We call this Plasma: electrons are stripped off the nuclei (since temperature is so high).

 Well, where are the electrons? They are floating around in that thick soup of Hydrogen and Helium nuclei. They are at the same temperature as the nuclei, but they're about 2000-7500 times lighter. Therefore they're much faster.

 Something interesting happens: In the Red Giant phase these electrons take responsibility for the pressure (called electron degeneracy) inside the core. Furthermore, this pressure doesn't depend on temperature. The latter means that temperature increases while pressure stays the same.

 So throughout all these thousands/millions of years
........while helium accumulates in the core
................due to hydrogen fusing in a shell
........................the core contracts slightly
................................and increases its temperature from 10 mill. K to 100 mill. K
........................................without increasing the core pressure
................................................that is without any relief.

 Right.

 Due to helium fusing
........energy is produced in the core
................temperature goes up
........................but pressure stays the same (due to electron degeneracy)
................................-> so no relief for the core
I.e. more and more helium fuses and the temperature climbs till virtually all helium fuses.

 Surprise: For a change this doesn't happen on an astronomical time scale, but within seconds!

 All Helium fuses almost instantly - the
 
 

and electron degeneracy is destroyed.

 By the way, what do you get when something burns? ______

 So Helium fusion produces ________
 

Let's accelerate our lecture.

 For reasons not mentioned the star actually becomes dimmer for a while. Then Helium fuses in a shell (smoothly) while hydrogen fuses in an outer shell, so the star becomes fainter. Now, usually (that is for light enough stars) the Carbon flash doesn't occur.

 For more reasons not explained, while the core shrinks, the outer layers of the star (call it atmosphere or envelope) expand.

..Expansion -
.........Cooling -
..............Nuclei and electrons recombine to form atoms.
...................This envelope is pushed away
..........................and forms a so called Planetary Nebula (Cateye Nebula, (c) STScI ),

again an unfortunate name because it doesn't have anything to do with planets (Arny p.401).
Still heated from its center star (actually only the carbon core remained) it emits light, primarily of course the red hydrogen line.

For some spectra of planetary nebulae, look here: John Talbot's Laser Stars pages .

What happens to the core?

 It's carbon, which appears as graphite on Earth, so it would be black.

 However, its temperature is high and its density is huge (because it's about as small as our earth), so it's rather a diamond.

A single white dwarf is circled in this image, (c) AURA / STScI .    Well, it's a White Dwarf and it continues to shine white (10,000 K), but dim (it's small), until all the stored heat is given off (nuclear fusion isn't going on anymore). It will do so for billennia and trillennia. When it eventually becomes cold, it becomes a black dwarf (what are the chances of detecting one?) and the force that keeps it from totally imploding is again electron degeneracy.

That's actually a misnomer: when these objects were first discovered in the 1700's their round, smudgy appearance resembled the appearance of planets.  Nebula stands for haze, cloud, fog.
Since more powerful telescopes (better resolution) and photography were built and invented since then, their true nature became known: a stellar atmosphere gently pushed off by its dying star leaving a white dwarf behind.  The non-violent expulsion of gas coupled with a special immediate environment around the star produces various intricate structures.  The intense UV radiation from the hot white dwarf heats up the blown off gas and makes it glow in various colors.
 
 

How Planetary Nebulae originate

Sirius B & A Sirius of course appears as the brightest star as seen from Earth.  It's a normal MS star. Its companion, "B", was a heavier MS star, died younger, developed into a RG, and is now a wd.  The planetary nebula phase lasts such a short time that it's over by now for B.	Inside a Red Giant During the Red Giant phase, a slow stellar wind spews out gas.  Since the RG is cold, atoms in the wind can accumulate to molecules, even (opaque) dust.
In the transition phase between the RG and white dwarf, a fast wind catches up to the slower gas: this collision produces intricate structures (e.g. Eskimo, Glowing Eye, Helix). The collision heats up the gas, making it glow.  In addition, the hot white dwarf emits intense UV radiation, making the ejected gases fluoresce.  And visible light from the white dwarf  is scattered by the dust.

 
 

The Hubble pictures of Planetary Nebulae

If you want see how some of these look like through a telescope, go to the Planetary Nebulae Observer's Home Page and check out the image galleries 8, 9, and 10.

Cat's Eye	Eskimo	Stingray	Egg
Hour glass	Symbiotic stars	Cotton Candy	Butterfly or Twin Jet (VLT at left) ; Left Right
Dumbbell (VLT)			PN's in Large Magellanic Cloud
Glowing Eye	Helix (AAT)	Southern Ring	Ring (M. Reble at left); L R

 
 

(Arny p.402) What about high mass stars (> 8 sun masses)?

Note that for the following, stars experience the same formation, Main Sequence and Helium flash as the low mass stars. Simply their way of dying is dramatically different.

Here, temperature in the carbon core is high enough,
.... so Carbon does ignite (combining with Helium) ,
........ forming Oxygen (it's 1 billion K, its density is 1 mill. times higher than on earth, so it's not breathable)
............ then Oxygen ignites
................ forming Neon (all the while hydrogen, helium, carbon, etc. are fusing in shells)
.................... and so on, every second element in the periodic system
........................ until Iron is formed in the core.
 

Why does it stop with iron? __________________________
 

Well, nuclear fusion sets energy free, but beginning with Iron nuclear fusion requires energy. The stored heat is not enough to keep iron burning and since iron fusion could not supply the energy need, the chain of element formation must stop here.

 In the beginning of the universe, only the lightest elements were formed: 90% Hydrogen, nearly 10% Helium, and traces of Lithium.

 We have seen that a star can produce some of the elements between Hydrogen and Iron.

 What about the other elements between H and Fe? __________________________________ __________________________________

 How did they leave the star? _________________________________________

 What about the elements beyond Iron? ________________________________________,
only such an event is powerful enough to fuse elements beyond Iron.
 

(Arny p.404) So what happens with the non-fusing iron core?

 THE   MOST   DRAMATIC   EVENT   IMAGINABLE:
 
 

All this happens within 1 second!

A supernova detected in a spiral galaxy, a single (exploding) star rivaling the brightness of a hundred billion stars in its own galaxy, (c) AURA / STScI .   This produces so much energy that elements heavier than Iron form (all the way to Uranium) and that the star increases its luminosity by a factor of 1 billion for several weeks, making a supernova as bright as its own entire galaxy before it fades almost into obscurity:

 The remaining star can be a neutron star, which balances gravity with its own tightly packed neutrons.

Vela Supernova Remnant in x-rays, 1999 stamp (c) German Postal Services .  But the expanding outer layers become an irregular nebula (a supernova remnant) around the neutron star, which make beautiful photographs.

 Supernovae in our galaxy close to our sun can outshine all stars, which happened in
...1054 (recorded by the Chinese ; for an account see the Kopernik Astronomical Society ), now the Crab Nebula in Taurus, (c) AURA / STScI
...1572 (recorded by Tycho Brahe)
...1604 (recorded by Johannes Kepler, Galileo Galilei)
 

They should happen every 300 years in a galaxy, so we're overdue - maybe it happens during our life time, so watch out!
 

Earlier we talked about low (0.08 to about 5-10 sun masses) and high (about 5-10 to more than 20 sun masses) mass stars. Mass is the single most important property of a star. It determines the evolution of a star as well as its lifetime (e.g. lower mass stars live longer). In all the above discussed cases this means the initial mass, which decreases by less than 1% from birth to onset of a planetary nebula or a supernova. So mass is fairly constant.
 

However, mass of a star can drastically change due to 3 reasons:

1. The star is one component of a binary system (remember, that these are used to determine stellar masses due to Kepler's 3rd) and it accretes mass from its component, which can happen any time during the star's lifetime, provided that they are close enough so that matter can flow from one to the other. How? What happens? See ya later ...
2. The already mentioned planetary nebula (ejection of star's atmosphere) or supernova.
3. Very high mass stars (m > 15 sun masses) have strong solar winds, which can shed up to 60% of the high mass star during its short lifetime.
 

Recently stars have been discovered that are called hypergiants, e.g. Eta Carinae, (c) AURA / STScI , which at 100 sun masses weighs in as the heaviest star known in our galaxy. In 1842 and 1843 it had a major outburst that made it the brightest star in the sky for several years. The shed dust and gas of this super wind was imaged by Hubble. Since it is so massive, it has such a short lifetime that it can go supernova any time soon (in the next thousands of years). Let's talk about case 2 first.

(Arny ch.14) The atmosphere is blown off and it remains the star's core, whose mass is only a fraction of the star's original mass.

 Mass of left-over core
< 1.4 sun masses _________________
between 1.4 and 3.0 sun masses _________________
> 3.0 sun masses _________________

 , so the original mass may be responsible for possibilities of carbon, oxygen fusing, etc., evolutionary track, the way of death ... But it's the mass of the remaining core that determines the star's coffin.

 Well, we had White Dwarfs and Neutron Stars.

 A star left with more than 3.0 sun masses after the supernova will collapse further because even the tightly packed neutrons can't stand gravity.

 Gravity pulls everything inside, the star collapses totally under its weight and becomes a

 It does not have a definite radius (well, its radius is zero). Yet there is a defined distance from the black hole's singularity. It is called the Schwarzschild radius or event horizon.

 Event horizon (about 9 km for a black hole of 3 sun masses): Gravity is so strong inside the event horizon that nothing, not even light, can escape. Seen from the outside, a space traveller approaching the black hole would seem to take forever to fall in (time dilation as predicted by general relativity).  Matter that is very close to the black hole can be sucked into the black hole, it accelerates and gives off x-rays.  Confused? That's good.

In the hypothetical case that our Sun would (magically) become a one solar mass black hole, what would happen to Earth in its orbit?  (Why can the Sun not become a black hole?)
 

 Among these effects the theory of a moon coming to close to Saturn, being ripped apart and forming the rings, is important for the following.

 Go to (Arny p.417; Ch/Mc p.348, Fig. 15.2) .

 One topic, that we left out, are binary stars. Two stars of any mass orbit each other. Which one dies first? _________________

 Say, one of them ends up with less 1.4 sun mass after its Red Giant phase. It becomes a _________________ . Also assume that they're pretty close - maybe Earth-Sun distance.

 Eventually, the other star starts dying too and becomes a Red Giant.
 
 

Red Giant and White Dwarf orbiting each other.  Accretion of mass by the white dwarf.  Violent ignition of hydrogen on the wd's surface.  (c) Redshift 3. Now, parts of the atmosphere of the red giant may expand so far (beyond its own Roche lobe) that they experience more gravitational force from the white dwarf than from their own star.  What happens? ...  Correct.  The transferred mass is accreted by the white dwarf and circulates it.  More and more mass is thrown onto the white dwarf. This gas, mostly hydrogen, on the white dwarf's surface becomes hotter and hotter.

 

Nova Cygni 1992,(c) AURA / STScI . Eventually ...

 What happens to the white dwarf's brightness? ...

It goes ...

NOVA.

 The remaining Helium and Hydrogen just sits on the white dwarf's surface until enough matter from the red giant is accreted to ignite hydrogen again (can take several thousands years).
 

That's the basic theory of a Nova.
 

There are a couple of twists associated with mass accretion.

 One is that binary stars are observed where the white dwarf is less massive than its main sequence companion. It seems that the lighter star died first. What's the correct theory for this phenomenon? ...
 

(Arny p.418) The other is: What could happen to a white dwarf if it accretes so much mass that it crosses the limit of 1.4 sun masses? ...

Check out the spectra of Nova Sgr 2001 .

Neutron Stars / Pulsars

- What's the cause of Northern Lights?
- What are conservation laws?

 We used one of the latter, in particular conservation of energy. E.g. the energy radiated from a star equals the energy produced in the star.

 Now we'll use the conservation of Angular Momentum.

 Imagine that you and some other people are sitting on the edge of a merry-go-around. Then the other people crawl into the center. What happens to you? ...

 That's because Angular Momentum L is conserved. L = m r² w = const. Here m is everybody's mass (which remains constant), r the distance from people to the center, which becomes smaller. Consequently, since L is conserved, the angular velocity w must increase.

Crab Nebula, at its center lies a Pulsar, (c) AURA / STScI. As a star shrinks from its main sequence size to the "Manhattan" size of a Neutron star (r becomes smaller) , its angular velocity must increase, since angular momentum is constant. It rotates faster. In fact, our sun needs about 25-29 days to rotate. A neutron star, being much smaller, rotates much faster, a millisecond to about 5 sec for some neutron stars.

Hubble Sees a Neutron Star Alone in Space, (c) AURA / STScI .  Furthermore, the neutron star's magnetic field is conserved. Now that the neutron star is very small, the magnetic field close to its surface is very large.

 What does this have to do with the Northern lights?
As in the Earth's case, electric charges (for Earth from Sun, for neutron star from Interstellar Medium) are captured by the magnetic field and spiral around the magnetic field lines onto the magnetic poles. Being accelerated, these electric charges radiate radiowaves, which extend from the magnetic axis.

 Every time one of the pulsar's magnetic poles faces the Earth (within seconds or fractions of a second), we can register radiowaves from this "lighthouse beacon". (Visible light and x-rays are detected to a lesser degree.)
 
 

Black Holes

If the mass of the remaining core exceeds 3 M_o , the neutrons' pressure can't balance gravity
-> collapse of the star to a point like object (singularity) with infinite density follows.

 The theory is worked out well, the most likely candidate for a Black Hole is Cygnus X-1 (Einstein's general relativity applies) . Check the Sky & Telescope May 1996 issue for more candidates.
Furthermore, cores of galaxies (e.g. our own Milky Way) are believed to be made up of supermassive black holes (several million M in a singularity).

 Properties:

 - singularity, i.e. point like object with M > 3 sun masses and infinite density

 - no definite surface

 - Schwarzschild radius = 3 [km]
-> event horizon (same as Schwarzschild radius) would be at 9 km = 6 miles around a point containing 3 sun masses

- event horizon -> everything falling inside, is never seen again, even light can't escape

 - matter, prior to falling in, is greatly accelerated -> x-rays send out in huge amounts
(Clue: strong x-rays observed from Cygnus X-1, which orbits HDE 226868)

 - mass so great that light from farther object is bent by Black Hole
-> gravitational lens producing two or smeared out ring like images of farther object
 
 
 

Variable Stars

 AAVSO - American Association of Variable Star Observers
 
 
 
 

TABLE  1

  more spectral sequence web sites: http://home.achilles.net/~jtalbot/data/plots.html , spectral sequence .
 
 

TABLE  3
 

TABLE  4
 

TABLE  5

Table 6,  More Observational Properties
of Main Sequence Stars
TABLE  6

The following table shows solar system abundances for some elements.  From the Periodic System of the Elements , 89 elements occur naturally.  Since our Sun contains about 99.8% of the solar system's mass, these numbers are valid for our Sun's composition as well.  And all other stars have similar abundances.  A common misconception is though that a casual look at spectral absorption lines (spectral classes) gives us the stars' compositions.  It doesn't.  Instead that casual look gives us the surface temperature.  But check my lecture on Measuring Stars on how a star's composition really is determined by looking very carefully at the absorption lines.
 
 

Table 7   Solar System Abundances

		Element	Abundance	.............			Element	Abundance
1	H	Hydrogen	1,000,000,000,000		26	Fe	Iron	32,000,000
2	He	Helium	98,000,000,000		27	Co	Cobalt	81,000
3	Li	Lithium	15		28	Ni	Nickel	1,800,000
4	Be	Beryllium	14		29	Cu	Copper	19,000
5	B	Boron	400				...
6	C	Carbon	350,000,000		79	Au	Gold	7
7	N	Nitrogen	93,000,000		80	Hg	Mercury	12
8	O	Oxygen	740,000,000		81	Tl	Thallium	7
9	F	Fluorine	36,000		82	Pb	Lead	110
10	Ne	Neon	120,000,000				...
11	Na	Sodium	2,000,000		90	Th	Thorium	1
12	Mg	Magnesium	38,000,000		91	Pa	Protactinium	-
13	Al	Aluminum	3,000,000		92	U	Uranium	.3
14	Si	Silicon	35,000,000
15	P	Phosphorus	370,000
16	S	Sulfur	19,000,000
17	Cl	Chlorine	190,000
18	Ar	Argon	1,000,000
19	K	Potassium	130,000
20	Ca	Calcium	2,200,000

The abundance for each element is listed with respect to hydrogen, i.e. for each one trillion hydrogen atoms there are  #n  atoms for each element  X .  (I didn't include all elements.)

References:

Cambridge Atlas of Astronomy

-> Time till He-flash p.251; central temperature and density p.252; spectroscopic characteristics p.242; MS examples p.241-2;

James Kaler

Stars and Their Spectra -> ...

Isaac Asimov

Die Schwarzen Löcher (Black Holes) -> Mass p.119; Luminosity p.119; # and % of stars in Milky Way p.120; MS lifetime p.122

Theodore P. Snow

Essentials of the Dynamic Universe -> Surface Temperature, absolute magnitude MV, color index B-V, bolometric correction B.C., Radius, Mass p.297

George O. Abell

Exploration of the Universe -> Spectroscopic characteristics p.419; time till He-flash p.562

B.W. Carroll, D.A. Ostlie

An Introduction to Modern Astrophysics   -> color index U-B

Jay Pasachoff

Astronomy -> Solar abundances of Elements (adopted from N. Grevesse and E. Anders)

Lori Allen and Karen M. Strom

Moderate-resolution Spectral Standards from 5600 to 9000 Å, in The Astronomical Journal, Volume 109, Number 3, 1379, March 1995, at http://donald.phast.umass.edu/data/tables/hystds/table1.html -> color index V-I

See also a short summary by Eric Weisstein at the University of Virginia at

http://scienceworld.wolfram.com/astronomy/Star.html

Credits:

Material created with support to AURA / ST ScI from NASA contract NAS5-26555 is reproduced here with permission.

Measuring Stars Lecture
* Atmosphere of Betelgeuse; courtesy of A. Dupree (CfA) and NASA
* Hubble Separates Stars In The Mira Binary System; courtesy of Margarita Karovska (Harvard-Smithsonian Center for Astrophysics) and NASA
* Hubble Catches Up with a Blue Straggler Star; courtesy of R. Saffer (Villanova University), D. Zurek (ST ScI) and NASA
* Star Birth in NGC 1850; courtesy of Ray Villard, Nino Panagia (STScI) and NASA
* Dense Globular Cluster M15; courtesy of Robert Irion (Univ. CA, Santa Cruz), Barbara Kennedy (Pennsylvania State Univ.), Ray Villard (STScI) and NASA

Favorite Hubble Images Lecture
* Release of Hubble Space Telescope; courtesy of Space Shuttle Endeavor STS-61 crew and NASA
* The Orion Trapezium and their (artificial) Airy-disks; courtesy of John Bally, Dave Devine, and Ralph Sutherland (CITA) and NASA
* Comet P/Shoemaker-Levy 9 (1993e); courtesy of Hal Weaver, T. Ed Smith (STScI) and NASA
* Comet Shoemaker-Levy 9 impact sites on Jupiter; courtesy of Hubble Space Telescope Comet Team and NASA
* Aurora on Saturn; courtesy of J.T. Trauger (Jet Propulsion Laboratory) and NASA
* Pluto and Charon - before adjustment of focus; courtesy of ESA and NASA
* Pluto and Charon - after adjustment; courtesy of R. Albrecht (ESA/ESO), Keith S. Noll (STScI) and NASA
* Star Birth in M16 Eagle Nebula; courtesy of Jeff Hester, Paul Scowen (Arizona State University) and NASA
* Proplyds in Orion Nebula; courtesy of John Bally, Dave Devine, and Ralph Sutherland (CITA) and NASA
* Destruction of Proto-Planetary Disks in Orion's Trapezium Explained; courtesy of John Bally, Dave Devine, and Ralph Sutherland (CITA) and NASA
* Final Blaze Of Glory Of Sun-Like Stars, the Butterfly Nebula; courtesy of Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA
* Helix Nebula; courtesy of C. Robert O'Dell, Kerry P. Handron (Rice University) and NASA
* Stingray Nebula; courtesy of M. Bobrowsky (Orbital Sciences Corp.) and NASA
* Egg Nebula; courtesy of R. Sahai and J. Trauger (JPL), the WFPC2 Science Team and NASA
* NICMOS Peers Into Heart Of Dying Star; courtesy of Rodger Thompson, Marcia Rieke, Glenn Schneider, Dean Hines (University of Arizona), Raghvendra Sahai (Jet Propulsion Laboratory), NICMOS Instrument Definition Team and NASA
* Hourglass Nebula; courtesy of R. Sahai, J. Trauger (JPL), the WFPC2 Science Team and NASA
* Cat eye Nebula; courtesy of J.P. Harrington, K.J. Borkowski (University of Maryland) and NASA
* Doomed Star Eta Carinae; courtesy of Jon Morse (University of Colorado) and NASA
* Supernova Blast Begins Taking Shape; courtesy of Chun Shing Jason Pun (NASA/GSFC), Robert P. Kirshner (Harvard-Smithsonian Center for Astrophysics) and NASA
* Cygnus Loop; courtesy of Jeff Hester (Arizona State University) and NASA
* Oxygen-Rich Supernova Remnant in the Large Magellanic Cloud; courtesy of J. Morse (ST ScI) and NASA
* Cartwheel Galaxy; courtesy of Kirk Borne (ST ScI) and NASA
* Galactic Building Blocks; courtesy of Rogier Windhorst, Sam Pascarelle (Arizona State University) and NASA
* Hubble Astronomers Use Lens In Nature To Uncover Most Distant Galaxy In The Universe; courtesy of Marijn Franx (University of Groningen, The Netherlands), Garth Illingworth (University of California, Santa Cruz) and NASA
* Gravitational Lens in Cluster Cl0024+1654; courtesy of W.N. Colley and E. Turner (Princeton University), J.A. Tyson (Bell Labs, Lucent Technologies) and NASA
* Hubble Deep Field; courtesy of R. Williams and the HDF Team (ST ScI) and NASA
* Black Hole in the galaxy NGC 4261; courtesy of H. Ford and L. Ferrarese (JHU) and NASA

Stellar Evolution Lecture
* Orion Nebula Mosaic; courtesy of C.R. O'Dell, S.K. Wong (Rice Univ.) and NASA
* Giant Starbirth Region In Neighboring Galaxy; courtesy of Hui Yang (University of Illinois) and NASA
* "Proplyds'' in Orion Nebula; courtesy of C.R. O'Dell (Rice Univ.) and NASA
* Inside Red Dwarfs (Gl752b); courtesy of Ray Villard (STScI), Jeffrey Linsky (JILA) and NASA
* Brown Dwarf Gliese 229B; courtesy of T. Nakajima and S. Kulkarni (Caltech), S. Durrance and D.Golimowski (JHU) and NASA
* Small Star (Gl623b); courtesy of C. Barbieri (Univ. of Padua) and NASA
* White Dwarf Stars in Globular Cluster M4; courtesy of Harvey Richer (University of British Columbia, Vancouver, Canada) and NASA
* Supernova in Galaxy M51; courtesy of Robert P. Kirshner (Harvard-Smithsonian Center for Astrophysics) and NASA
* Supernova 1987A Rings; courtesy of Christopher Burrows (ESA/STScI) and NASA
* Crab Nebula; courtesy of Jeff Hester and Paul Scowen (Arizona State University) and NASA
* Black Hole Candidate: Victim of Misatken Identity; courtesy of Right -- Wachter et. al. (University of Washington) and NASA, Left -- Paul Schmidtke (Arizona State University) and Cerro Tololo Interamerican Observatory, Chile
* Nova Cygni 1992; courtesy of F. Paresce, R. Jedrzejewski (STScI) and NASA
* Blobs in Space: The Legacy of a Nova; courtesy of Mike Shara, Bob Williams, and David Zurek (Space Telescope Science Institute), Roberto Gilmozzi (European Southern Observatory), Dina Prialnik (Tel Aviv University) and NASA
* Hubble Sees a Neutron Star Alone in Space; courtesy of Fred Walter (State University of New York at Stony Brook) and NASA