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Jerry
2008-Oct-31, 05:58 PM
There has been a relatively large number of papers and articles about White Dwarf stars and their collective properties lately; and in my limited study of these objects, I have been looking for evidence of critical mass: A size limit, after which the population drops-off rapidly, if not completely. The reasoning is thus: In theory, White Dwarfs accrete matter to the Chandrasahkar limit, then explode. If our sample of White Dwarfs is complete enough, we may see a normalized distribution with a long-tail on one end, but a sharp-tail on the exploding end. (tick tick tick...) I haven't seen evidence of this in the papers I have reviewed, but I wonder if I just missed it.

This paper:

http://lanl.arxiv.org/abs/0809.3914v1
Plots two curtailed distributions, but they seem to be due to selection effect limits rather than size. There doesn't seem to be a strong correlation between mass and temperature; and it seems to me that the accretion theory implies that there should be.

See also

http://lanl.arxiv.org/abs/0810.5123v1

Photometric constraints on white dwarfs and the identification of extreme objects

BigDon
2008-Oct-31, 07:15 PM
Are there debris clouds to account for this Jerry?

(We both know I'm not a physicist, that's just the first thing I thought of)

Jeff Root
2008-Oct-31, 07:24 PM
I may be missing something that you are saying, but my understanding is
that stars do not normally accrete matter. That might not be true of white
dwarf stars, though. Stars like the Sun vaporize any small bodies that fall
close to them, then solar wind blows away the vapor. White dwarfs might
not have strong enough solar wind to do that.

-- Jeff, in Minneapolis

John Mendenhall
2008-Oct-31, 07:32 PM
Neat graph from Wiki:

http://en.wikipedia.org/wiki/Image:WhiteDwarf_mass-radius.jpg

This is for non-rotating white dwarves. For all real ones, the limits do not apply. (!)

How's that for a non-answer?

Regards, John M.

grant hutchison
2008-Oct-31, 07:33 PM
I may be missing something that you are saying, but my understanding is
that stars do not normally accrete matter.
Jeff, an accreting white dwarf is the standard model for Type 1a supernovae.

Grant Hutchison

grant hutchison
2008-Oct-31, 07:39 PM
This is for non-rotating white dwarves. [bee in bonnet] The plural, everywhere outside Tolkien's writing, is "dwarfs". [/bee in bonnet]

Grant Hutchison

Celestial Mechanic
2008-Oct-31, 08:53 PM
Ply them with enough mead and I suppose they would. ;) ;) ;)

mugaliens
2008-Oct-31, 10:05 PM
[bee in bonnet] The plural, everywhere outside Tolkien's writing, is "dwarfs". [/bee in bonnet]

Grant Hutchison

From Merriam-Webster: Inflected Form(s): plural dwarfs \ˈdwȯrfs\ also dwarves \ˈdwȯrvz\
I was taught "dwarves, as in knives," but it appears it could be either.

For knives, this isn't the case: Inflected Form(s): plural knives \ˈnīvz\ - it's the only entry.
By the way, I love the imagery of the OP's title - quite appropriate given the details in the OP!

grant hutchison
2008-Oct-31, 10:48 PM
From Merriam-Webster: Inflected Form(s): plural dwarfs \ˈdwȯrfs\ also dwarves \ˈdwȯrvz\
I was taught "dwarves, as in knives," but it appears it could be either.Tolkien resuscitated the long-dead "dwarves" plural in 1937 for The Hobbit, and wrote that he used it solely to set his dwarves apart from the other usages of the word "dwarf".

Grant Hutchison

slang
2008-Oct-31, 11:35 PM
[bee in bonnet] The plural, everywhere outside Tolkien's writing, is "dwarfs". [/bee in bonnet]

If you doubt this is possible, how is it there are PYGMIES + DWARFS??

timb
2008-Oct-31, 11:48 PM
There has been a relatively large number of papers and articles about White Dwarf stars and their collective properties lately; and in my limited study of these objects, I have been looking for evidence of critical mass: A size limit, after which the population drops-off rapidly, if not completely. The reasoning is thus: In theory, White Dwarfs accrete matter to the Chandrasahkar limit, then explode. If our sample of White Dwarfs is complete enough, we may see a normalized distribution with a long-tail on one end, but a sharp-tail on the exploding end. (tick tick tick...) I haven't seen evidence of this in the papers I have reviewed, but I wonder if I just missed it.

This paper:

http://lanl.arxiv.org/abs/0809.3914v1
Plots two curtailed distributions, but they seem to be due to selection effect limits rather than size. There doesn't seem to be a strong correlation between mass and temperature; and it seems to me that the accretion theory implies that there should be.


What's the "accretion theory"?

According to White Dwarf Mass Distribution in the SDSS (http://http://lanl.arxiv.org/abs/astro-ph/0612277) the largest white dwarf known has a mass of 1.33 Msol.

grant hutchison
2008-Nov-01, 12:50 AM
[bee in bonnet] The plural, everywhere outside Tolkien's writing, is "dwarfs". [/bee in bonnet]If you doubt this is possible, how is it there are PYGMIES + DWARFS??I'm sorry, I don't understand your question.

"Dwarfs" is the traditional plural for all usages.
"Dwarves" is an old variant which was popularized by Tolkien, applied specifically to his dwarf miners with beards and big axes:
In English the only correct plural of dwarf is dwarfs, and the adjective is dwarfish. In this story dwarves and dwarvish are used, but only when speaking of the ancient people to whom Thorin Oakenshield and his companions belonged.

JRR Tolkien, Introduction to The Hobbit (1937)Disney's Snow White and the Seven Dwarfs was released in the same year as The Hobbit and used the standard spelling, but others have since borrowed Tolkien's spelling style when describing similar creatures in fantasy writing and gaming.

It's a good idea not to call real people of short stature either dwarfs or dwarves, since many of them find both usages insulting, but especially the latter.

Other technical usages, like "white dwarf" stars, take the plural "dwarfs".

Grant Hutchison

slang
2008-Nov-01, 01:10 AM
I'm sorry, I don't understand your question.

I probably should have linked it to the appropriate origin of said quote.. but it's probably not quite fitting here. Googling the capitalized part should give a direct reference to my probably not in very good taste joke. It was not serious, that much I can say without references.

grant hutchison
2008-Nov-01, 01:24 AM
I probably should have linked it to the appropriate origin of said quote.. Ah, OK. I tracked it down with your hints. Sorry to have dropped the ball on that one. :) I'm not a big fan of Pharyngula.

(But hey, you got a free grammar lecture. :doh:)

Grant Hutchison

Spaceman Spiff
2008-Nov-01, 03:03 AM
Non-accreting white dwarfs, which probably constitute the vast majority, simply cool over time, like a glowing piece of charcoal pulled out of a pile of hot coals. The cooling time scale does depend on mass in a less than simple way, but otherwise their surface temperatures should not scale with mass in any kind coherent way (with the exception that more massive white dwarfs start off hotter).

Accreting white dwarfs are those in tight binaries with a normal star, which has filled its tidal radius and so is transferring mass to the white dwarf. The white dwarf gets rid of this mass in different ways depending on the rate of accretion and other parameters (including the white dwarf mass): dwarf novae, novae, Type 1a supernovae. The surface and interior temperatures of accreting white are therefore not simply monontonically decreasing functions of time.

timb
2008-Nov-01, 03:41 AM
Non-accreting white dwarfs, which probably constitute the vast majority

The OP apparently thinks all white dwarves accrete until they turn into type 1a supernovae.

What I find surprising is that so many massive stars end up as white dwarfs. If I'm reading right, even stars 2, 3 or 4 times as massive as the sun will typically lose enough mass to end their lives as WDs rather than neutron stars or black holes.

Jerry
2008-Nov-01, 04:21 AM
What's the "accretion theory"?

According to White Dwarf Mass Distribution in the SDSS (http://http://lanl.arxiv.org/abs/astro-ph/0612277) the largest white dwarf known has a mass of 1.33 Msol.

At a limit of ~1.4 m(solar) white dwarfs are thought to -sometimes - accrete matter to this limit, generally by stealing from a companion. If the largest white dwarf in the SDSS has a mass of 1.33, that is consistent with the theory...or is the theory being used to constrain the mass?

Tobin Dax
2008-Nov-01, 05:56 AM
At a limit of ~1.4 m(solar) white dwarfs are thought to -sometimes - accrete matter to this limit, generally by stealing from a companion. If the largest white dwarf in the SDSS has a mass of 1.33, that is consistent with the theory...or is the theory being used to constrain the mass?
Did you read the paper, Jerry? I've started looking through it, but I've decided that you can read it and answer your own question.

timb
2008-Nov-01, 05:57 AM
I don't think so. Why don't you read the paper? The OP seemed to imply there should be numerous white dwarfs just below some sharp cut-off mass. Most white dwarfs are small and massive ones are rare, so the cut-off could be quite hard to distinguish from the taper.

neilzero
2008-Nov-01, 12:47 PM
All white dwarfs rotate with respect to something = all is relative.
Less than one revolution per day is likely very rare for white dwarfs.
One revolution per day will not much affect the accretion rate.
Typical accretion rates are negligible, but not zero.
The high surface gravity means weak solar wind even if 25,000 degrees k is typical white dwarf surface temperature = mass loss is close to negligible after the 2nd week.
If the mass grows one percent per week due to accretion, the white dwarf will become a neutron star (without a super nova, but at perhaps double the mass that that neutron stars typically form in a super nova = The shock waves of a super nova allow compact stars to form at lower mass? Neil

timb
2008-Nov-01, 01:01 PM
All white dwarfs rotate with respect to something = all is relative.


Rotation isn't relative.



Less than one revolution per day is likely very rare for white dwarfs.
One revolution per day will not much affect the accretion rate.
Typical accretion rates are negligible, but not zero.


If they're negligible then you can neglect them without affecting the analysis. That's what negligible means. Many if not most white dwarfs will be solitary or in wide binaries. How much do you expect them to accrete and from where? the interstellar medium?


The high surface gravity means weak solar wind even if 25,000 degrees k is typical white dwarf surface temperature = mass loss is close to negligible after the 2nd week.
If the mass grows one percent per week due to accretion

That sounds like an incredibly high accretion rate to me.

Spaceman Spiff
2008-Nov-01, 02:10 PM
The OP apparently thinks all white dwarves accrete until they turn into type 1a supernovae.

What I find surprising is that so many massive stars end up as white dwarfs. If I'm reading right, even stars 2, 3 or 4 times as massive as the sun will typically lose enough mass to end their lives as WDs rather than neutron stars or black holes.

Yes, it is amazing. In fact depending on the star's heavy element mix, that upper mass limit may be as high as 8 solar masses. Sirius B (a white dwarf of 1 solar mass) was probably ~5 solar mass main sequence star (http://adsabs.harvard.edu/abs/2005ApJ...630L..69L). Stars lose a lot of mass while on the red and asymptotic giant branches. There is also a reasonably well established relation between the initial and final mass of the star (http://adsabs.harvard.edu/abs/2008arXiv0807.3567S) (as a non-accreting white dwarf) -- they scale together. So the paucity of "high mass" white dwarf stars is a function of the relative paucity of massive stars.

And no, most white dwarf stars simply cool and dim for aeons; only those found in tight binary systems can accrete appreciable mass and produce fireworks.

And what a white dwarf will do when you increase its mass depends on circumstances: initial mass, mass accretion rate, and the composition of of the white dwarf, to name those off the top of my head. It is a fallacy that carbon/oxygen white dwarf stars (likely the majority of them out there) simply collapse to neutron stars by adding mass beyond the "Chandrasekhar Limit". Instead, as the mass approaches this limit their interiors change their equation of state (due to the accompanying increase in density) just as carbon fusion begins to simmer, resulting in the star having a very bad day (boom!). In fact this "Chandrasekhar Limit" is only an idealized (and asymptotic) limiting mass -- it is never realized in nature because the equation of state changes as the density increases.

As I understand it: that neutron stars do form is in large part a consequence of their initial conditions (electron degenerate state in a iron rich core) at the center of a massive star.

mugaliens
2008-Nov-01, 09:55 PM
Tolkien resuscitated the long-dead "dwarves" plural in 1937 for The Hobbit, and wrote that he used it solely to set his dwarves apart from the other usages of the word "dwarf".

While it was originally published, to wide acclaim, in 1937, it wasn't until it was published in paperback in the United States in 1966 that the interest in the Hobbit was renewed for the modern generations. Furthermore, Tolkien was English. We Yanks do things a bit different, some times.

grant hutchison
2008-Nov-01, 10:20 PM
We Yanks do things a bit different, some times.Yes, Tolkien's formation is certainly used much more in the USA than in Britain. Difficult to know if old JRRT would have been pleased or not. :lol:

But the usage notes I gave above (http://www.bautforum.com/1355065-post12.html) are quite general: you'll find them applied in both American and British English.

Grant Hutchison

timb
2008-Nov-01, 10:41 PM
Yes, it is amazing. In fact depending on the star's heavy element mix, that upper mass limit may be as high as 8 solar masses. Sirius B (a white dwarf of 1 solar mass) was probably ~5 solar mass main sequence star (http://adsabs.harvard.edu/abs/2005ApJ...630L..69L). Stars lose a lot of mass while on the red and asymptotic giant branches.


Nice nebulae, pretty nebulae. The amount of material collectively ejected into interstellar space by "low" mass AGB stars must be much much greater than the contribution from supernovae, so the common idea that all the heavy elements "we're made of" came from supernovae is wrong. Of course the word "heavy" is open to interpretation (like a lot of words astronomers use: how hot is "hot"? how small is a "dwarf"? how late is "late"? how metallic is "metal"?)


There is also a reasonably well established relation between the initial and final mass of the star (http://adsabs.harvard.edu/abs/2008arXiv0807.3567S) (as a non-accreting white dwarf) -- they scale together. So the paucity of "high mass" white dwarf stars is a function of the relative paucity of massive stars.


Fig.3 seems to have plenty of points more than four sigma from the theoretical curve.



And no, most white dwarf stars simply cool and dim for aeons; only those found in tight binary systems can accrete appreciable mass and produce fireworks.

And what a white dwarf will do when you increase its mass depends on circumstances: initial mass, mass accretion rate, and the composition of of the white dwarf, to name those off the top of my head. It is a fallacy that carbon/oxygen white dwarf stars (likely the majority of them out there)


What are the alternatives? helium dwarfs would arise from low mass stars that cannot burn helium. These are common but they have very long MS lifetimes, so existing helium dwarfs would have been formed by mass loss in a binary system. That must be rare. I've seen mention of oxygen/neon dwarfs as the most massive.

timb
2008-Nov-01, 10:47 PM
At a limit of ~1.4 m(solar) white dwarfs are thought to -sometimes - accrete matter to this limit, generally by stealing from a companion. If the largest white dwarf in the SDSS has a mass of 1.33, that is consistent with the theory...or is the theory being used to constrain the mass?

A couple of other contenders. V445 Puppis (http://lanl.arxiv.org/abs/0805.2540) 1.35, RS Oph (http://http://lanl.arxiv.org/abs/0807.1251) also 1.35.

Jeff Root
2008-Nov-02, 08:48 AM
More off-topic.



calf calves
elf elves
half halves
hoof hooves
knife knives
leaf leaves
life lives
loaf loaves
scarf scarves
self selves
sheaf sheaves
shelf shelves
staff staves
wharf wharves
wife wives
wolf wolves

-- Jeff, in Minneapolis

Whirlpool
2008-Nov-02, 09:14 AM
LOL.
I thought this thread is about another thing .

:doh:

Tobin Dax
2008-Nov-02, 01:02 PM
wolf - wolves
woof - wooves
worf - worves

:think: Hmm. Maybe not.

Spaceman Spiff
2008-Nov-02, 05:32 PM
Nice nebulae, pretty nebulae. The amount of material collectively ejected into interstellar space by "low" mass AGB stars must be much much greater than the contribution from supernovae, so the common idea that all the heavy elements "we're made of" came from supernovae is wrong. Of course the word "heavy" is open to interpretation (like a lot of words astronomers use: how hot is "hot"? how small is a "dwarf"? how late is "late"? how metallic is "metal"?)

Right, but what matters is how much of that mass loss contains elements cooked up by the star --- ejecting material of the same composition of the original star does not change the elemental abundances of the galaxy. Many elements are created, either via fusion or via slow neutron capture, by red giant and especially AGB (aymptotic giant branch) stars -- yet many elements are not and have their origins in high mass stars or in their demise, or in Type 1a supernovae (massive white dwarf stars in tight binary systems accreting matter from the companion star up towards the Chandrasekhar Limit).

timb
2008-Nov-02, 11:26 PM
Right, but what matters is how much of that mass loss contains elements cooked up by the star --- ejecting material of the same composition of the original star does not change the elemental abundances of the galaxy. Many elements are created, either via fusion or via slow neutron capture, by red giant and especially AGB (aymptotic giant branch) stars -- yet many elements are not and have their origins in high mass stars or in their demise, or in Type 1a supernovae (massive white dwarf stars in tight binary systems accreting matter from the companion star up towards the Chandrasekhar Limit).

For sure. There's no doubt that AGB stars have cooked up C, N, O, and Ne in large quantities by fusion (and much smaller amounts of other elements by slow neutron capture), which are "heavy" relative to the primordial elements H, He & Li. The only element I can think of that is present in human bodies in substantial quantities and is not on that list is Ca. Of course there's a bunch of trace elements we can't live without.

Spaceman Spiff
2008-Nov-03, 03:14 PM
For sure. There's no doubt that AGB stars have cooked up C, N, O, and Ne in large quantities by fusion (and much smaller amounts of other elements by slow neutron capture), which are "heavy" relative to the primordial elements H, He & Li. The only element I can think of that is present in human bodies in substantial quantities and is not on that list is Ca. Of course there's a bunch of trace elements we can't live without.

Yeah, and we happen to sit on a hunk of Mg, Si, and Fe....:)