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trinitree88
2011-Dec-22, 06:44 PM
I have a specific question about Deneb. Deneb is the tail star of Cygnus the Swan, swimming down the Milky Way in your winter constellations in the Northern Hemisphere. SEE:http://www.google.com/imgres?q=cygnus+the+swan&um=1&hl=en&sa=N&rlz=1R2GGIC_enUS460&biw=992&bih=500&tbm=isch&tbnid=oaY4QARenNgAYM:&imgrefurl=http://mail.colonial.net/~hkaiter/starweb/section5/coracygnus5/coracygnus5.htm&docid=Bd2fGr7KA9sm1M&imgurl=http://mail.colonial.net/~hkaiter/starweb/section5/coracygnus5/cygnus.gif&w=300&h=246&ei=23nzTpDTLaju0gGG66HCAg&zoom=1&iact=hc&vpx=275&vpy=186&dur=1734&hovh=196&hovw=240&tx=127&ty=108&sig=101469945271561140868&page=4&tbnh=126&tbnw=154&start=30&ndsp=10&ved=1t:429,r:6,s:30
As a blue supergiant, it is a candidate as a progenitor for a relatively nearby supernova, since it resides in the Milky Way galaxy with us.

Perikles
2011-Dec-22, 06:47 PM
Er - what is the question?

antoniseb
2011-Dec-22, 06:55 PM
... As a blue supergiant, it is a candidate as a progenitor for a relatively nearby supernova, since it resides in the Milky Way galaxy with us.
I assume you mean to ask this rather than state it.

trinitree88
2011-Dec-22, 07:06 PM
I have a specific question about Deneb. Deneb is the tail star of Cygnus the Swan, swimming down the Milky Way in your winter constellations in the Northern Hemisphere. SEE:http://www.google.com/imgres?q=cygnus+the+swan&um=1&hl=en&sa=N&rlz=1R2GGIC_enUS460&biw=992&bih=500&tbm=isch&tbnid=oaY4QARenNgAYM:&imgrefurl=http://mail.colonial.net/~hkaiter/starweb/section5/coracygnus5/coracygnus5.htm&docid=Bd2fGr7KA9sm1M&imgurl=http://mail.colonial.net/~hkaiter/starweb/section5/coracygnus5/cygnus.gif&w=300&h=246&ei=23nzTpDTLaju0gGG66HCAg&zoom=1&iact=hc&vpx=275&vpy=186&dur=1734&hovh=196&hovw=240&tx=127&ty=108&sig=101469945271561140868&page=4&tbnh=126&tbnw=154&start=30&ndsp=10&ved=1t:429,r:6,s:30
As a blue supergiant, it is a candidate as a progenitor for a relatively nearby supernova, since it resides in the Milky Way galaxy with us.It's about ~60,000 times as luminous as the sun, ~ 20 solar masses, and is pegged by Hipparcos at ~ 1550 light-years. At that distance we would be completely safe from radiation effects and would be treated to a great show, should it go.
In older threads I had suggested that somebody monitor the spectra of good, close, possible progenitors of type II (core collapse) supernovae with filters specifically characterized to search for iron absorption lines. Such lines (Fraunhofer lines) occur when the outer atmosphere of a star extends far enough away that it can cool and begin to form a diffuse gas of atoms, which then absorb when cool, the same lines they would emit when hotter as bright line spectra. Why? Because the star transitions from hydrogen burning, eventually, to helium burning, and then to heavier elements, C,N,O, Ne, Mg, S, Fe....with iron the last before it goes supernova, as I understand it. Several different models for the last stage, I've seen over the years in the literature, with most of them indicating that the accumulation of iron in the core begins within 2-20 years of the star going supernova. Little iron should show in the star's spectra before that, though it would depend upon the particular presolar nebula's isotopic mix. Most supergiants form not in the gas-rich inner Milky Way, but in the periphery of the spiral arms, where the gas density is lower.
Today I checked out Deneb's spectra. The iron lines are quite distinct, but I have no idea if they have evolved in recent years, which might indicate concentrations presaging a supernova, or nothing of particular importance. Question: Where do I go to source an archive of Deneb's spectra? I searched the web for a while and found very little of use? Thanks pete SEE:http://en.wikipedia.org/wiki/Deneb

Swift
2011-Dec-22, 07:12 PM
I merged trinitree88's two threads about this

antoniseb
2011-Dec-22, 07:21 PM
Hi Trinitree, I expect that stars in the 20+ solar mass range will not be ejecting Carbon, or anything heavier out of their cores through convection, and explosions such that they might color the photosphere. I think spectral clues about one of these monsters being ready to blow will be few or non-existent.

Jeff Root
2011-Dec-22, 07:29 PM
What?? Wait-- You didn't just suggest that iron generated in
the last few years before a star goes supernova could show
up in that star's spectrum before it goes supernova, did you?
I must have misunderstood!

-- Jeff, in Minneapolis

trinitree88
2011-Dec-22, 07:37 PM
Hi Trinitree, I expect that stars in the 20+ solar mass range will not be ejecting Carbon, or anything heavier out of their cores through convection, and explosions such that they might color the photosphere. I think spectral clues about one of these monsters being ready to blow will be few or non-existent.

Hi. There are lots of iron-group bright-lines indicating evolved nucleosynthesis, and I found an absorption spectrum I liked finally, but lost it in amending my first post, hence the double somehow. I'll persist. thanks. ...left you a PM pete

PraedSt
2011-Dec-22, 07:51 PM
Hi. There are lots of iron-group bright-lines indicating evolved nucleosynthesis, and I found an absorption spectrum I liked finally, but lost it in amending my first post, hence the double somehow. I'll persist. thanks. ...left you a PM peteWould you mind posting a couple of links for the spectra?

antoniseb
2011-Dec-22, 07:58 PM
Hi. There are lots of iron-group bright-lines indicating evolved nucleosynthesis, ...
The Sun has lots of Iron group lines too. It didn't make the Iron and push it out to the photosphere, and I'd like to see some Fe/H data on Deneb before making any such assumption there.

trinitree88
2011-Dec-22, 08:02 PM
The Sun has lots of Iron group lines too. It didn't make the Iron and push it out to the photosphere, and I'd like to see some Fe/H data on Deneb before making any such assumption there.

Thanks. OK. I refound the spectrum, SEE: http://www.astrogeo.va.it/astronom/spettri/stelle-Aen.html ... and I'll search for a ratio in the literature on the Web

PraedSt
2011-Dec-22, 08:52 PM
Thanks. OK. I refound the spectrum, SEE: http://www.astrogeo.va.it/astronom/spettri/stelle-Aen.html ... and I'll search for a ratio in the literature on the WebThat link doesn't work for me.

Romanus
2011-Dec-23, 01:25 AM
IIRC, a star generates an inert iron core in an extremely short period of time (in fact, each successive stage of "burning" in the core takes less and less time as game day approaches), perhaps in as little as a week--far too short for any signature of it to show up at the surface, even if it weren't buried under many overlying, fusing shells.

Tensor
2011-Dec-23, 03:18 AM
Thanks. OK. I refound the spectrum, SEE: http://www.astrogeo.va.it/astronom/spettri/stelle-Aen.html ... and I'll search for a ratio in the literature on the Web

I could get there pete, but it told me I was forbidden to access the server.

Tensor
2011-Dec-23, 04:12 AM
In older threads I had suggested that somebody monitor the spectra of good, close, possible progenitors of type II (core collapse) supernovae with filters specifically characterized to search for iron absorption lines. Such lines (Fraunhofer lines) occur when the outer atmosphere of a star extends far enough away that it can cool and begin to form a diffuse gas of atoms, which then absorb when cool,

snip...

Today I checked out Deneb's spectra. The iron lines are quite distinct, but I have no idea if they have evolved in recent years, which might indicate concentrations presaging a supernova, or nothing of particular importance. Question: Where do I go to source an archive of Deneb's spectra? I searched the web for a while and found very little of use? Thanks pete SEE:http://en.wikipedia.org/wiki/Deneb

Actually, Pete, it's Nickel that is produced last. I know, I know, everybody knows that Iron is the end and everything higher than Iron needs an energy input to fuse. Well, not quite. Stars in silicon burning can get an alpha particle (helium nucleus) to fuse with a iron nucleus to produce nickel. Ni56 (28 protons), then decays by beta emission (positron, ~ 6 days ) to Cobalt. The Co56 (27 protons) then decays, also by positron beta (~77 days) to iron (Fe56 (26 protons)). The timeframe I've seen for Silicon burning is 1 day. Oxygen burning is ~1 year and Neon burning doesn't produce a high enough temperature to produce either Iron or Nickel. I don't see how any amount of iron, that was produced in the star, would end up in the spectrum. Now, if there was iron in the star when it was formed, then, as antoniseb said, you might see the absorption lines. And with only one day of silicon burning, I doubt you'd even see absorption lines from Nickel or Cobalt.

Jeff Root
2011-Dec-23, 05:19 AM
Is there any reason to *ever* see *any* of the isotopes
produced in a star in that star's atmosphere? I wouldn't
think so, but maybe it depends on the particular star?

-- Jeff, in Minneapolis

Tensor
2011-Dec-24, 04:25 AM
Is there any reason to *ever* see *any* of the isotopes
produced in a star in that star's atmosphere? I wouldn't
think so, but maybe it depends on the particular star?

-- Jeff, in Minneapolis

From what I've been able to find, there is one class of stars that probably does have material produced in the star, found in their atmosphere. Stars with masses of 6-9 times the mass of the sun should initiate carbon burning, but it will depend on several factors like amount carbon available, mixture and location within the star, etc). Stars with 9-11 time the mass of the sun will initiate carbon burning, but whether or not they initiate neon burning is, again, dependent on several factors. Stars in the 9-11 mass range, that initiate neon burning, will tend to blow off their outer layers, including their atmospheres, and in these particular cases, there should be some of the carbon produce in the star represented in that atmosphere, prior to it getting blown off. In getting rid of their outer layers, they will form planetary nebular and will expose the neon-oxygen core (there is also magnesium and sodium in the core).

There are a series of papers here (http://www.aanda.org/articles/aa/pdf/2006/11/aa3043-05.pdf), here (http://164.15.125.39/~siess/pmwiki/pub/Papers/aa476.pdf), and here (http://164.15.125.39/~siess/pmwiki/pub/Papers/aa512.pdf) that provide the details of giant stars. If any of the above explanation is wrong, the fault is mine, and not the fault of Lionel Siess (http://www-astro.ulb.ac.be/~siess/) the author of the papers.

Tim Thompson
2011-Dec-24, 11:10 PM
Try these papers, citations & references. Contacting the authors directly might also prove revealing, where practical.

Spectral Changes in Deneb, 1887-1964
http://adsabs.harvard.edu/abs/1965ApJ...142.1028L

Anomalous line profiles for Fe II (42) multiplet in the spectrum of Deneb
http://adsabs.harvard.edu/abs/1978SvAL....4..151L

A Spectral Analysis of Deneb (A2 Iae)
http://adsabs.harvard.edu/abs/2000A%26A...364..237A
http://adsabs.harvard.edu/abs/1999PASP..111..917A

Time, spatial, and spectral resolution of the H-alpha line formation region of Deneb and Rigel with the VEGA/CHARA Interferometer
http://adsabs.harvard.edu/abs/2010A%26A...521A...5C

trinitree88
2011-Dec-28, 04:11 PM
Try these papers, citations & references. Contacting the authors directly might also prove revealing, where practical.

Spectral Changes in Deneb, 1887-1964
http://adsabs.harvard.edu/abs/1965ApJ...142.1028L

Anomalous line profiles for Fe II (42) multiplet in the spectrum of Deneb
http://adsabs.harvard.edu/abs/1978SvAL....4..151L

A Spectral Analysis of Deneb (A2 Iae)
http://adsabs.harvard.edu/abs/2000A%26A...364..237A
http://adsabs.harvard.edu/abs/1999PASP..111..917A

Time, spatial, and spectral resolution of the H-alpha line formation region of Deneb and Rigel with the VEGA/CHARA Interferometer
http://adsabs.harvard.edu/abs/2010A%26A...521A...5C

Tim, Tensor & al. Thanks for the input. I don't have an ABS subscription so I can't open those files, but I'll keep pluggin away. Happy New Year. pete

grapes
2011-Dec-28, 04:56 PM
I have a specific question about Deneb. Deneb is the tail star of Cygnus the Swan, swimming down the Milky Way in your winter constellations in the Northern Hemisphere. Just a small nit. Cygnus is usually considered a summer constellation in the North--and Deneb is part of the so-called Summer Triangle asterism, along with Vega and Altair.

Tensor
2011-Dec-28, 10:49 PM
Tim, Tensor & al. Thanks for the input. I don't have an ABS subscription so I can't open those files, but I'll keep pluggin away. Happy New Year. pete

Pete, all of Tim's links have either a link to a arXiv PDF or a scanned link to the actual article in HTML. The only exception is "A Spectral Analysis of Deneb (A2 Iae) which can be found here (http://articles.adsabs.harvard.edu//full/2000A%26A...364..237A/0000237.000.html) in HTML.

trinitree88
2011-Dec-30, 06:10 PM
Just a small nit. Cygnus is usually considered a summer constellation in the North--and Deneb is part of the so-called Summer Triangle asterism, along with Vega and Altair.

grapes. Yep. Pardon my schoolboy error. When I teach the circumpolar constellations, altazimuth...etc. my little sky map has Cygnus nearby, and it's so recognizable, I usually include it with the others, it sure does disappear for a while in the winter.:rolleyes: kudos. pete


p.s. you can tell I'm a theorist

George
2012-Jan-01, 03:00 PM
I thought the more massive the star, the less the convective transfer. Apparently, however, O & B class stars have some convection, but this may be limited to the core zone. How would the heavy metals surface in a monster like Deneb?

trinitree88
2012-Jan-01, 04:26 PM
I thought the more massive the star, the less the convective transfer. Apparently, however, O & B class stars have some convection, but this may be limited to the core zone. How would the heavy metals surface in a monster like Deneb?

George. There's still this....SEE:http://chandra.harvard.edu/press/00_releases/press_101800.html
where it appears convective models assuming the lack thereof in massive stars is incorrect. pete

and this: http://arxiv.org/PS_cache/arxiv/pdf/1110/1110.5345v1.pdf

George
2012-Jan-01, 07:55 PM
George. There's still this....SEE:http://chandra.harvard.edu/press/00_releases/press_101800.html
where it appears convective models assuming the lack thereof in massive stars is incorrect.
I see. I found this (http://agenda.albanova.se/conferenceDisplay.py?confId=2032) also, which claims subsurface convection might explain things.

From this (http://www.physics.uc.edu/~sitko/Astrophysics-II/26-MassiveStars/26-MassiveStars.pdf) there is the comment (pg 7) that some dredging can take place due to mass loss and convection.

The latter link failed for me.

SagittariusAStar
2012-Jan-04, 10:10 PM
Is there any reason to *ever* see *any* of the isotopes
produced in a star in that star's atmosphere? I wouldn't
think so, but maybe it depends on the particular star?

-- Jeff, in Minneapolis

Yes, this was first seen by Paul Merrill in 1952--not for Deneb, but for other stars. See the story on pages 106-109 of

The Alchemy of the Heavens: Searching for Meaning in the Milky Way by Ken Croswell.