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trinitree88
2010-Jun-04, 05:29 PM
People argue over whether type 1a's are deflagrations or delayed detonations. A new generation of neutrino detectors may definitively settle the point. SEE:http://arxiv.org/PS_cache/arxiv/pdf/1006/1006.0490v1.pdf
A detonation generally produces much stronger shock fronts.

Jerry
2010-Jun-06, 07:11 PM
I'm skeptical about whether or not neutrino detectors could settle the debate. There were only a handful of neutrinos (above background) observed from 1987A; the closest modern-era supernova event. Another close event would produce a lot of neutrinos; but other data (including the possible detection of progenitors) would be much more definitive.

It can be argued that the debate should already be settled, or at least heavily weighted toward a dual - detonation scenario. This model is more consistent with polarization and other expansion velocity data. The accretion model has a lot of inertia; meaning it was taught as virtual gospel before observation data made it less plausible. Then there is always the possibility both models work; or both are wrong.

trinitree88
2010-Jun-07, 04:59 PM
I'm skeptical about whether or not neutrino detectors could settle the debate. There were only a handful of neutrinos (above background) observed from 1987A; the closest modern-era supernova event. Another close event would produce a lot of neutrinos; but other data (including the possible detection of progenitors) would be much more definitive.

It can be argued that the debate should already be settled, or at least heavily weighted toward a dual - detonation scenario. This model is more consistent with polarization and other expansion velocity data. The accretion model has a lot of inertia; meaning it was taught as virtual gospel before observation data made it less plausible. Then there is always the possibility both models work; or both are wrong.

Jerry. As an interested bystander, I think the issue comes down to neutrino opacity. At one time, many moons ago,
we were led to believe that neutrinos pass merrily through everything, like lasers through glass. Gradually the words neutrino-opacity appeared at nuclear densities and beyond in compact objects...including core collapse supernovae calculations. So if a type 2 proceeds by detonation, the density falls off rapidly during the expansion, and the trapped neutrinos suddenly flash out in a prompt neutrino burst, pretty much over a narrow energy band (a little wider at the poles due to parity effects). However if the initial expansion is a slower deflagration, they leak out, cooling the neutrino sea interior, and a wider energy band with a lower average inferred temperature should be expected.
My recollection of events from SN1987a is that there were several papers saying the neutrinos appeared to have been pulsed, with a period of ~( 1.5 seconds ?) ...indicating the core was bouncing a bit like a Cepheid with a very high Reynolds number. No?
At any rate, it gives them something to look for, and me something to think about. pete

StupendousMan
2010-Jun-07, 06:04 PM
My recollection of events from SN1987a is that there were several papers saying the neutrinos appeared to have been pulsed, with a period of ~( 1.5 seconds ?) ...indicating the core was bouncing a bit like a Cepheid with a very high Reynolds number. No?


You can see the arrival times of the neutrinos detected at Brookhaven and at Kamiokande in this little lecture

http://spiff.rit.edu/classes/phys200/lectures/sn1987a_2/sn1987a_2.html

and read the technical papers for full details. The numbers are pretty small to claim any sort of periodicity, I would say.

trinitree88
2010-Jun-08, 08:37 PM
You can see the arrival times of the neutrinos detected at Brookhaven and at Kamiokande in this little lecture

http://spiff.rit.edu/classes/phys200/lectures/sn1987a_2/sn1987a_2.html

and read the technical papers for full details. The numbers are pretty small to claim any sort of periodicity, I would say.

Thanks, Stu. My less than stellar memory of the event was quite off, this is the paper I was thinking about (although I can't access it). Maybe you'll find it interesting, if you can. pete SEE:http://www.springerlink.com/content/g62126j1542265kn/

Roger E. Moore
2010-Jun-18, 06:26 PM
People argue over whether type 1a's are deflagrations or delayed detonations. A new generation of neutrino detectors may definitively settle the point. SEE:http://arxiv.org/PS_cache/arxiv/pdf/1006/1006.0490v1.pdf
A detonation generally produces much stronger shock fronts.

This puzzles me. All my reading online suggests that neutrinos are not produced by type 1a supernovae, but are instead known from core-collapse type II blasts.

Jerry
2010-Jun-19, 01:52 AM
The standard model for Type Ia is challenged by several observations: 1) A much broader range in luminosity than thought as recently as a decade ago. 2) A LOT of evidence of assymetry in the expansion curves. 3) A lack of a clear, definitive line between type Ia an a laundry list of 'hypernove'.

Tensor
2010-Jun-21, 03:52 AM
Still trying to push the same old tired ideas Jerry? Even though, in this thread (http://www.bautforum.com/showthread.php/103003-Discovery-that-quasars-don-t-show-time-dilation-mystifies-astronomers) you were continually shown to be wrong about this. What was so interesting about that thread was 90-95% of the material I got to refute you, was from the very papers you thought were supporting your position. So I really look forward to the papers you will bring in to support you position here.

OK, let's go through this one at a time:


The standard model for Type Ia is challenged by several observations: 1) A much broader range in luminosity than thought as recently as a decade ago.

The range in luminosity is mainly due to dust. This causes problems in making sure the brightness of different SN1a are really the same intrinsic brightness. The range in luminosity basically disappears when Type 1a supernovas are looked at in Near Infrared. There are other type event that closely resemble type 1a supernova optically. However, they can be isolated from type 1a supernova through spectral signature, or how they appear at different points in the spectrum.


2) A LOT of evidence of assymetry in the expansion curves.

There can be two currently known reasons for the asymmetry. One reason has been found to be due to the merger of two white dwarfs, the so called dual detonation events. This pushes the merged object over the Chandrasekar limit. And while the luminosity can be similar or brighter than type 1a explosions, they are different spectroscopically. There is also evidence for asymmetric explosions. In these cases, the brightness depends on the viewing angle. However, not sure why you bring this up, as it is well known in astrophysical community. This was worked out and has been taken into SN1a observations since the late 80s - early 90s. Are you that far behind?


3) A lack of a clear, definitive line between type Ia an a laundry list of 'hypernove'.

Not sure where you are getting your information (well, I'm sure, I invite anyone to the previous linked thread to see the difference between what you claimed the paper said and what the paper actually said.) but there are quite a few definitive ways to distinguish type 1a supernova from what you call hypernova. Or Type 1a supernova from dual detonation events or asymmetric explosions. Of course, you don't accept the evidence or the explanation of the evidence, (or, according to some of your posts, simply misunderstand the evidence) but that has nothing to do with the evidence being available.

Jerry
2010-Jun-21, 04:47 AM
http://arxiv.org/abs/1006.3576

apparently Maoz et al didn't get the memo on the party line

The supernova delay time distribution in galaxy clusters and implications for Type-Ia progenitors and metal enrichment


This implies 50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from double-degenerate (DD) models, which generically have ~t^{-1} shapes over a wide range of timescales, match the data, but only if their predictions are scaled up by factors of 5-10. Single degenerate (SD) DTDs always give poor fits to the data, due to a lack of delayed SNe and overall low numbers of SNe... Our results support the existence of a DD progenitor channel for SNe Ia, if the overall predicted numbers can be suitably increased.

Tensor
2010-Jun-21, 01:53 PM
Ahhh, Jerry, Jerry, Jerry. I knew you'd come through for me. In my last post, I said the following:


What was so interesting about that thread was 90-95% of the material I got to refute you, was from the very papers you thought were supporting your position. So I really look forward to the papers you will bring in to support you position here.

And, what happens in your first post? You come through for me. I didn't have to go searching for papers refuting your claims. Again, you provided the paper for me.



http://arxiv.org/abs/1006.3576

apparently Maoz et al didn't get the memo on the party line

Apparently, you didn't actually read the paper and simply pulled out random quotes from the abstract. Let's got through this and see where you misunderstood this one, shall we?



The supernova delay time distribution in galaxy clusters and implications for Type-Ia progenitors and metal enrichment

From the title, you wouldn't think that it supports or doesn't support SN 1a.

I see you got this from the abstract....



This implies 50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from double-degenerate (DD) models, which generically have ~t^{-1} shapes over a wide range of timescales, match the data, but only if their predictions are scaled up by factors of 5-10. Single degenerate (SD) DTDs always give poor fits to the data, due to a lack of delayed SNe and overall low numbers of SNe... Our results support the existence of a DD progenitor channel for SNe Ia, if the overall predicted numbers can be suitably increased.

But you seemed to miss this in the Abstract:

We compile recent measurements of the Type-Ia SN (SN Ia) rate in galaxy clusters at redshifts from z = 0 out to z = 1.45, just 2 Gyr after cluster star formation at z ≈ 3. We review the plausible range for the observed total iron-to-stellar mass ratio in clusters, based on the latest data and analyses, and use it to constrain the time-integrated number of SN Ia events in clusters. With these data, we recover the DTD of SNe Ia in cluster environments. The DTD is sharply peaked at the shortest time-delay interval we probe, 0 < t < 2.2 Gyr, with a low tail out to delays of ∼ 10 Gyr, and is remarkably consistent with several recent DTD reconstructions based on different methods, applied to different environments.

My bold. What they are saying here Jerry, is that their work matches the DTD (Delay Time Distribution, The time supernova explode after a burst of star forming activity) within clusters. And, as a bonus, it matches other DTD reconstructions "based on different methods applied to different environments. In other words Jerry, just in the abstract, they are stating the SN1a data matches everyone else's.

The bolded part is what you missed in the abstract:

We perform forward modeling to test DTD models from the literature, requiring that they simultaneously reproduce the observed cluster SN rates and the observed iron-to-stellar mass ratios. A parametrized power-law DTD of the form t−1.1±0.1, starting at < 250 Myr and extending to a Hubble time, can satisfy both constraints. Shallower power laws, such as t−1/2 cannot, assuming a single DTD, and a single star-formation burst (either brief or extended) at high z. This implies 50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from double-degenerate (DD) models, which generically have ∼ t−1 shapes over a wide range of timescales, match the data, but only if their predictions are scaled up by factors of 5 − 10.

Jerry, the part you quoted are the results of the part where they are trying to model the DTD rate forward. They apply certain constraints, run the model forward, and see if it matches current observations . In this case, they start with a starburst formation at around 3 Gly. But you didn't quote that part of the abstract, why? What they are saying is that the current model, using a parametrized power law of the DTD (T-1) can match the current observations. A shallower power law (~T-1/2) can't match it using a single progenitor DTD. Dual detonations DTD models fit quite well (their power law is naturally shaped as T-1), but there have to be more of them, by a factor of 5 to 10, to be viable models. That many dual detonation SN1a isn't currently supported by observation.

So, what we have here is just another case of you, simply misunderstanding what the body of the paper is saying or cherry picking the quotes you think support your position. They go through the exact steps for everything in the body of the paper. Their first conclusion states that current observations match quite well with their work here, not to mention match other work. Jerry, why don't you actually read the whole paper and not just the abstract?

Jerry
2010-Jun-21, 05:23 PM
I could have snipped out of their conclusion, which says exactly the same thing:


Physical DD models from the BPS simulations we have examined can match the observations, provided they are scaled up in numbers by factors of 5 − 8. On the other hand, SD models, on their own, fail because they do not produce SNe at late delays, as implied by the data. Our results thus provide strong support for
the double-degenerate SN Ia progenitor scenario.

Why would the authors expressly state that their results provide strong support for the double-degenerate SN Ia progenitor scenario if they mean to say just the opposite? This is nuts!

Returning to the abstract:


An alternative scenario of a single, prompt, SN Ia population, but a composite star-formation history in clusters, consisting of a burst at high z, followed by a constant star-formation rate, can reproduce the SN rates, but is at odds with direct measurements of star formation in clusters at 0 < z < 1.

The authors conclude that with their models they can almost mimick observations with a combination of DD (double degenerate) and single degenerate events, but not quite: The rate needs to be a little higher than what is currently observed.

In any case:

The very fact that they are comparing the rate us SD models with the DD models proves my point: There is current and open debate about the mechanism(s) involved in supernova type Ia events.

Tensor
2010-Jun-21, 07:18 PM
I could have snipped out of their conclusion, which says exactly the same thing:

Why would the authors expressly state that their results provide strong support for the double-degenerate SN Ia progenitor scenario if they mean to say just the opposite? This is nuts!

Maybe because they were looking at Binary Population Synthesis (BPS) modeling at the time. Instead of parametric modeling. SD events using a parametrization of T-1 fit quite well, with no scaling. Using BPS modeling, DD have to be scaled, by a factor 5 -8 to fit and even that doesn't fit well. Looking at figure five the caption mentions that if the DD model is scaled to optimal iron values, it doesn't fit observed low redshift cluster SN1e formation.


Returning to the abstract:
An alternative scenario of a single, prompt, SN Ia population, but a composite star-formation history in clusters, consisting of a burst at high z, followed by a constant star-formation rate, can reproduce the SN rates, but is at odds with direct measurements of star formation in clusters at 0 < z < 1.

The authors conclude that with their models they can almost mimick observations with a combination of DD (double degenerate) and single degenerate events, but not quite: The rate needs to be a little higher than what is currently observed.

Which is very probably due to their various assumptions and their use of BPS, which they acknowledge underestimates rates.


In any case:

The very fact that they are comparing the rate us SD models with the DD models proves my point: There is current and open debate about the mechanism(s) involved in supernova type Ia events.

No, there is not. Single detonation and dual detonation event are recognized by anyone working with SN. This paper acknowledges it. In fact, one of the paper's you gave a link to in that first thread, explained how to determine the difference between SD and DD by spectrography. But one thing I found very interesting here. You obviously can't be supporting DD as presented in this paper. From the paper:


As noted by pre- vious authors (e.g., Greggio 2005; Totani et al. 2008) a power-law dependence is generic to models (such as the DD model) in which the event rate ultimately depends on the loss of energy and angular momentum to gravitational radiation by the progenitor binary system. If the dynamics are controlled solely by gravitational wave losses.

The reason DD work so well is that their power law is close to T-1 because of Gravitation Radiation. Gravity waves, Jerry. Since you are so vocal in your arguments against gravitational waves, you can't very well agree to a process that depends on them, can you?

Jerry
2010-Jun-22, 02:31 AM
The reason DD work so well is that their power law is close to T-1 because of Gravitation Radiation. Gravity waves, Jerry. Since you are so vocal in your arguments against gravitational waves, you can't very well agree to a process that depends on them, can you?
What is curious about gravitational waves is that we can't detect them.

There is a nice update on the latest-and-greatest here:

http://arxiv.org/abs/1005.0026

The Role of Variations of Central Density Of White Dwarf Progenitors Upon Type Ia Supernovae


These observational findings are consistent with SNe Ia Ni-56 production in star-forming spiral galaxies some 0.1 solar masses higher - and therefore more luminous than in elliptical galaxies.

Tensor
2010-Jun-22, 04:00 AM
The reason DD work so well is that their power law is close to T-1 because of Gravitation Radiation. Gravity waves, Jerry. Since you are so vocal in your arguments against gravitational waves, you can't very well agree to a process that depends on them, can you? What is curious about gravitational waves is that we can't detect them.

Yes, and you have been quite vocal in your arguments claiming that as a result of not detecting them, we should discard General Relativity. Not to mention, that paper also requires a Lamda CDM model to be consistent. Something else you disagree with. So, the DD channel in that paper requires two things that you disagree with Gravitational Waves and a Lambda CDM model. Care to explain how you can support that model, when you don't support the assumptions going into that model?




There is a nice update on the latest-and-greatest here:

http://arxiv.org/abs/1005.0026

The Role of Variations of Central Density Of White Dwarf Progenitors Upon Type Ia Supernovae

Latest and greatest what? That paper, while trying to make sense of exactly how a SN1a goes up, assumes, for a SD event, that somewhere near the Chandrasekhar mass, while accreting material, it does explode. Which is what I've been saying all along and you seem to have a problem with. From the new link:


Accordingly, Type Ia properties are consistent with white dwarf progenitors.

I'll also point out that the Fisher may not be fitting the right constraints with his model. He does not take into account the effect of dust on observed luminosities of SN1a. This was pointed out by Kirshner (http://arxiv.org/pdf/0910.0257v1). A paper you were using to support another claim, a paper that turned out not to support your claim.

Jerry
2010-Jun-22, 06:02 AM
Yes, and you have been quite vocal in your arguments claiming that as a result of not detecting them, we should discard General Relativity. Not to mention, that paper also requires a Lamda CDM model to be consistent. Something else you disagree with. So, the DD channel in that paper requires two things that you disagree with Gravitational Waves and a Lambda CDM model. Care to explain how you can support that model, when you don't support the assumptions going into that model?
This is hardly the forum to defend atm concepts. For what its worth, I am quite comfortable with SD as being the likely major player in SN1a events; but I think the best observational data we have is consistant with the notion we do not have a good handle on the upper limit of supernovae Ia magnitudes; which, ironically would infer a greater cosmological constant...unless something else is wrong.

If relativistic physics are correct; there should be observable gravitational waves just as the Maxwellian theories required a measurable eather; so it is not as if we haven't missed before.

We observe braking in binary systems, so why no detectable waves? It is possible there is crushing local tidal effects; or possibly even electromagnetic braking. Silly? not according to :

http://arxiv.org/abs/1006.4112


Although the treatment in this paper is necessarily simplified, and many conditions must be met in order for a wind to operate as proposed, it is clear that magnetic braking cannot easily be ruled out as an important angular momentum sink. We finish by highlighting observational tests that in the next few years will allow an assessment of the importance of magnetic braking.


Latest and greatest what? That paper, while trying to make sense of exactly how a SN1a goes up, assumes, for a SD event, that somewhere near the Chandrasekhar mass, while accreting material, it does explode. Which is what I've been saying all along and you seem to have a problem with.
I said there are other alternatives; and not always concise definitions between type Ia and events of much greater magnitude. Fisher is having a hard time constraining nickle production; keeping the lumonsity down in near Chandrasekhar mass events. Too bright shouldn't be a problem - it only means these standard candles are less precise than many hoped.


I'll also point out that the Fisher may not be fitting the right constraints with his model. it does not take into account the effect of dust on observed luminosities of SN1a. This was pointed out by Kirshner (http://arxiv.org/pdf/0910.0257v1). A paper you were using to support another claim, a paper that turned out not to support your claim.My claim is that supernova magnitudes are often underestimated - and yes, dust is usually the reason.
http://arxiv.org/abs/0907.4495


We study different one-parametric models of type Ia Supernova magnitude evolution on cosmic time scales. Constraints on cosmological and Supernova evolution parameters are obtained by combined fits on the actual data coming from Supernovae, the cosmic microwave background, and baryonic acoustic oscillations. We find that data prefer a magnitude evolution such that high-redshift Supernova are brighter than would be expected in a standard cosmos with a dark energy component. Data however are consistent with non-evolving magnitudes at the one-sigma level, except special cases.
Sigh

Jerry
2010-Jun-24, 03:54 AM
http://arxiv.org/abs/1006.4391

Sub-Chandrasekhar White Dwarf Mergers as the Progenitors of Type Ia Supernovae

antoniseb
2010-Jun-24, 06:59 PM
http://arxiv.org/abs/1006.4391

Sub-Chandrasekhar White Dwarf Mergers as the Progenitors of Type Ia Supernovae

I saw this paper this morning. Nice work.


The lightcurves of most SN Ia are remarkably similar to
each other, and can be described empirically as a (nearly)
single-parameter family, in which the timescale and the maximum
luminosity are tightly correlated, with longer timescales
corresponding to higher luminosities and larger total energies
(Phillips 1993).

It does validate some things that you've been saying for some time. On the other hand, if you take their science and conclusions, the luminosity of Type 1a SN do not vary all that much and the light curves are still driven by Ni56. One of the things I like about this paper is the effective use of the IMF (initial mass function) for stars in galaxies, and the correlation to time since recent star formation epochs in the host galaxies. The net result, if these guys are right (and they make a pretty good case), is that SN Ia continue to be great cosmological measuring devices, but for precision work, we need a few from any given cluster, or better methods to sort out real brightness according to observed chemistry.

Jerry
2010-Jun-25, 11:05 PM
It does validate some things that you've been saying for some time.
I've said a lot of things, some of them contradictory.


On the other hand, if you take their science and conclusions, the luminosity of Type 1a SN do not vary all that much and the light curves are still driven by Ni56.That depends upon how much is 'not much'. A decade ago, not much was <0.4 magnitude. Today it is more like 1.2 and the there are some three-sigma things out there that are more like 2.6 magnitude. These higher magnitude events can be separated out by spectral hair-splitting; but it is diffcult to apply these tests at high redshifts; especially since the high redshift events routinely dial in brighter in the UV.


One of the things I like about this paper is the effective use of the IMF (initial mass function) for stars in galaxies, and the correlation to time since recent star formation epochs in the host galaxies. The net result, if these guys are right (and they make a pretty good case), is that SN Ia continue to be great cosmological measuring devices, but for precision work, we need a few from any given cluster, or better methods to sort out real brightness according to observed chemistry.

I agree; that is, within the context of the current concensus model, that as standard candles, the supernova Ia observational data point towards a 'dark energy' term; and if the absolute magnitudes at great distances are greater (as I suggest); even more so.

I disagree with the current trend in data analysis; and that is, to shuffle through the spectral detail until the curves line up as tight as possible and declare victory. (This approach lead to the 'single stretch factor' parameter that sent me off on a tangent in the first place.) We have enough observed events to sit back and look at the root distribution and apply simple Copernician sanity checks: What are the redshift/rise time/light-curve/luminosity relationships?

Nereid
2010-Jun-28, 03:25 PM
[...]

I disagree with the current trend in data analysis; and that is, to shuffle through the spectral detail until the curves line up as tight as possible and declare victory. (This approach lead to the 'single stretch factor' parameter that sent me off on a tangent in the first place.) We have enough observed events to sit back and look at the root distribution and apply simple Copernician sanity checks: What are the redshift/rise time/light-curve/luminosity relationships?
Have you taken into account the objective fact that your track record of accurately summarising papers is, um, not so good?

Might it be that what you disagree with is a strawman, a creature of your own imagination?

Jerry
2010-Jun-28, 04:03 PM
We discuss papers because it is easy to missunderstand the authors. If your are afraid of occasionally being wrong and don't say anything - you will be wrong and remain in the dark much of the time.

Drawing a conclusion that is different from the authors is sometimes a case of miss-interpretation; but it can also be a caes of applying more or less weight to the evidence at hand.

~2000, Goldhaber and Perlmutter published papers with a single, stretch parameter to correct the supernova Ia magnitude/curvelength relationship. Then they normalized to a redshift of z=0.48 and demonstrated that their residuals patterned in a tight distributon about the norm and declared victory.

I cried foul - you can't normalize about an arbitrary midpoint when the data is only anchored at one end - this would be suicidal in signal processing or any other scientific field relying upon extrapolative data= but it sailed though the astrophysical community with nare a wave. It has become very obvious since then that the single parameter approach was too optomistic: It now appears more luminous events generally have faster rise times and slower tailoffs. This artificially narrowed the magnitude bandwidth as determined using the 'stretch factor' methodology.

When I tried to explain this to people within the AP community; they insisted that I was miss-interpreting the data and and misrepresenting the paper, but I wasn't - I was working from the assumption that since the curves could be normalized without any weight allowed for either selection bias or dust attenuation meant there HAD to be a parametric trend within the data running opposite the authors assumptions. I applied ZERO WEIGHT to the fact that the authors came up with the answer they were expectiong. Today we know I was correct - the stretch factor assumptions were too simplistic; underestimated both the true range of observed luminosities and dust reddening. So sometimes it is the authors who miss-interprete the data, and not the critics.

Jerry
2010-Jul-04, 01:38 AM
Still trying to push the same old tired ideas Jerry? Even though, in this thread (http://www.bautforum.com/showthread.php/103003-Discovery-that-quasars-don-t-show-time-dilation-mystifies-astronomers) you were continually shown to be wrong about this. What was so interesting about that thread was 90-95% of the material I got to refute you, was from the very papers you thought were supporting your position. So I really look forward to the papers you will bring in to support you position here.

OK, let's go through this one at a time:



The range in luminosity is mainly due to dust. This causes problems in making sure the brightness of different SN1a are really the same intrinsic brightness. The range in luminosity basically disappears when Type 1a supernovas are looked at in Near Infrared. There are other type event that closely resemble type 1a supernova optically. However, they can be isolated from type 1a supernova through spectral signature, or how they appear at different points in the spectrum.

There can be two currently known reasons for the asymmetry. One reason has been found to be due to the merger of two white dwarfs, the so called dual detonation events. This pushes the merged object over the Chandrasekar limit. And while the luminosity can be similar or brighter than type 1a explosions, they are different spectroscopically. There is also evidence for asymmetric explosions. In these cases, the brightness depends on the viewing angle. However, not sure why you bring this up, as it is well known in astrophysical community. This was worked out and has been taken into SN1a observations since the late 80s - early 90s. Are you that far behind?


For having it 'all worked out'; this group of researchers are treating the topic rather tenderly:

K. Maeda, S. Benetti, M. Stritzinger3, F. K. Ropk, G. Folatelli, J. Sollerman, S. Taubenberger, K. Nomoto1, G. Lelouda, M. Hamuy, M. Tanaka, P. A. Mazzali, N. Elias-Rosa

Published in Nature 1 July 2010 issue.

An asymmetric explosion as the origin of spectral evolution diversity in type Ia Supernovae

http://arxiv.org/abs/1006.5888v1




Our interpretation suggests that two SNe with very similar light curve evolution may not necessarily produce exactly the same amount of 56Ni.

Similar light curve - different amounts of 56Ni produced. I which they were more explicit; but I think that means similar light curves may vary in luminosity - not including corrections for dust. It does allow for some spectral corrections; but then again:


...Here we report that the spectral diversity is a consequence of random directions from which an asymmetric explosion is viewed.

In this paragraph, do they mean line broadening; spectral signature; or both?

Finally:


Our finding regarding the explosion mechanism will lead to quantitative evaluation on the contribution of this random effect to the observed scatter in the SN Ia luminosities beyond the one-parameter description, as compared to other systematic effects, such as the stellar environment.

Which is a nice way of saying there is a lot more random scatter in the absolute magnitude of type Ia supernova than most researchers were willing to concede a decade ago.

Jerry
2010-Jul-07, 05:05 AM
http://arxiv.org/abs/1007.0910

On variations of the brightness of type Ia supernovae with the age of the host stellar population

This paper deals with metallicity rather than mechanism, but this is another emerging independant variable models need to deal with:


The central density of the progenitor is determined by the mass of the WD and the cooling time prior to the onset of mass transfer from the companion, as well as the subsequent accretion heating and neutrino losses. The dependence of this density on cooling time, combined with the result of our central density study, offers an explanation for the observed age-luminosity correlation: a longer cooling time raises the central density at ignition thereby producing less Ni-56 and thus a dimmer event. While our ensemble of results demonstrates a significant trend, we find considerable variation between realizations, indicating the necessity for averaging over an ensemble of simulations to demonstrate a statistically significant result.

Jerry
2010-Jul-28, 03:37 AM
http://arxiv.org/abs/1007.4751

Helium star evolutionary channel to super-Chandrasekhar mass type Ia supernovae
W. -M. Liu, W. -C. Chen, B. Wang, Z. W. Han

Abstract: Recent discovery of several overluminous type Ia supernovae (SNe Ia) indicates that the explosive masses of white dwarfs may significantly exceed the canonical Chandrasekhar mass limit. Rapid differential rotation may support these massive white dwarfs. Based on the single-degenerate scenario, and assuming that the white dwarfs would differentially rotate when the accretion rate $\dot{M}>3\times 10^{-7}M_{\odot}\rm yr^{-1}$, employing Eggleton's stellar evolution code we have performed the numerical calculations for $\sim$ 1000 binary systems consisting of a He star and a CO white dwarf (WD). We present the initial parameters in the orbital period - helium star mass plane (for WD masses of $1.0 M_{\odot}$ and $1.2 M_{\odot}$, respectively), which lead to super-Chandrasekhar mass SNe Ia. Our results indicate that, for an initial massive WD of $1.2 M_{\odot}$, a large number of SNe Ia may result from super-Chandrasekhar mass WDs, and the highest mass of the WD at the moment of SNe Ia explosion is 1.81

Jerry
2010-Jul-29, 05:10 AM
http://arxiv.org/abs/1007.4842v1

The Absolute Magnitudes of Type Ia Supernovae in the Ultraviolet



However, in the mid-UV the scatter is larger, ~1 mag, possibly indicating differences in metallicity. We find no strong correlation between either the UV light-curve shapes or the UV colors and the UV absolute magnitudes.

Local UV spectral were supposed to give us better clues about the most distant sample- that are brighter in the UV bands. I need to spend more time with this paper; I don't see how we can have tight curve/magnitude relationships in blue and total randomness in the UV.

Jerry
2010-Aug-08, 07:29 PM
http://arxiv.org/abs/1008.1024

This is a gutsy challenge; asking researchers to blindly compare their classification algorythms with other on the most distant and difficult sample, and at least four groups responded. It appears that no one emerged with clear bragging rights:

"For all of the entries the classification performance was significantly better for the spectroscopic training subset compared to the unconfirmed sample. The degraded performance on the unconfirmed sample was in part due to participants not accounting for the bias in the spectroscopic training sample. There is a large variation in the figure of merit and therefore we urge caution in using these evaluations to determine the best method. The quality of each implementation varies significantly between participants and therefore some improvements are needed
before drawing more clear conclusions. While this paper signifies the end of the SNPhotCC, we consider this
effort to be the start of a new era for developing classification methods with significantly improved simulation
tools. The results from this SNPhotCC may serve as a reference to assess future progress from using improved algorithms and improved simulations."

Loud applause for everyone involved in this unique study. We may get to the bottom of the supernova well yet.

Jerry
2010-Aug-26, 04:43 AM
http://arxiv.org/abs/1008.4126

Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe


We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe.

Jerry
2010-Sep-13, 04:17 AM
Characterizing the contaminating distance distribution for Bayesian supernova cosmology

]http://arxiv.org/abs/1009.1903

This paper is somewhat of a follow-up of the Supernovae Challenge paper posted above; the authors are examining how redshift distance blurs the boundries between supernova types in different photometric bandwidths. They build a model reshifted data set, then compare the distribution with the actual distribution observed in the SLOAN survey. They find significant variation between the artificial and real distribution and discuss several possible reasons for the disparity.

It is a very technical paper, but it is nice to add it to this thread as a reference.

Edited to Add: This paper references the Homeier Paper, The Effect of Type Ibc Contamination in Cosmological Supernova Samples http://arxiv.org/abs/astro-ph/0410593v1; which more-or-less kicked of the challenge to determine how well current supernovae segregation algorythms can discriminate between types of supernovae at high redshefts.

trinitree88
2010-Sep-23, 04:12 PM
For having it 'all worked out'; this group of researchers are treating the topic rather tenderly:

K. Maeda, S. Benetti, M. Stritzinger3, F. K. Ropk, G. Folatelli, J. Sollerman, S. Taubenberger, K. Nomoto1, G. Lelouda, M. Hamuy, M. Tanaka, P. A. Mazzali, N. Elias-Rosa

Published in Nature 1 July 2010 issue.

An asymmetric explosion as the origin of spectral evolution diversity in type Ia Supernovae

http://arxiv.org/abs/1006.5888v1



Similar light curve - different amounts of 56Ni produced. I which they were more explicit; but I think that means similar light curves may vary in luminosity - not including corrections for dust. It does allow for some spectral corrections; but then again:


In this paragraph, do they mean line broadening; spectral signature; or both?

Finally:



Which is a nice way of saying there is a lot more random scatter in the absolute magnitude of type Ia supernova than most researchers were willing to concede a decade ago.

Jerry This is interesting, that at this late date, the realization that supernovae are asymmetrical is intrinsic to the observed morphological characteristics, spectral evolutions, and light curves. It was for exactly that reason that I gave my talk at Vassar Ciollege in Nov of 92, on "Parity, Pulsars and Supernova Remnants", then a similar talk at Williams in 93, and Harvard 94 at the AAPT. Most of the authors are from Asia, and Europe except one from Cal, but you'd expect news to move better than that in the post-clipper-ship era. Surprising. pete

Jerry
2010-Sep-23, 06:44 PM
It is extremely difficult to let go of a cherished paradyne. (No penalty here for the use of the P word, this is the one case where it is completely appropriate.)

Here is another recent development:

http://arxiv.org/abs/0908.1918v2



We deduce that SNe 1986G, 2003gs, 2003hv, and 2006gt were fast declining objects that shared some interesting photometric characteristics. These objects were subluminous in the optical band passes, but their near-IR maximum light absolute magnitudes were statistically equal to those of the slow decliners and mid-range decliners. Also, the near-IR maxima of these four objects apparently occurred prior to the time of B-band maximum light. In the case of SN 2003gs we can say that the near-IR maxima did not occur “late,” i.e. a few days after T(Bmax). Type Ia SNe that had late near-IR maxima (SNe 1991bg, 1999by, 2005bl, 2005ke, and 2006mr) were subluminous at the times of the IR maxima. There appears to be a bimodal distribution of near-IR absolute magnitudes of Type Ia SNe at maximum light.
Which group a particular object falls into depends on whether it peaked late or early.

Remember a few papers ago it was asserted that SNIa remain very good standard candles - in the near infrared; now it appears there may be two branches in the near-IR as well.

tusenfem
2010-Sep-23, 07:21 PM
It is extremely difficult to let go of a cherished paradyne. (No penalty here for the use of the P word, this is the one case where it is completely appropriate.)

Paradyne???????????

Celestial Mechanic
2010-Sep-24, 04:37 AM
It is extremely difficult to let go of a cherished paradyne. (No penalty here for the use of the P word, this is the one case where it is completely appropriate.)
Fear not! I only penalize for use of the pretentious phrase "paradigm shift". I have found that people who use that phrase have either read Kuhn or (more likely) heard of Kuhn and think they now know how science works and that this random thought might be the long-awaited "paradigm shift".

Jerry
2010-Oct-13, 08:30 PM
HUBBLE SPACE TELESCOPE STUDIES OF NEARBY TYPE IA SUPERNOVAE: THE MEAN MAXIMUM
LIGHT ULTRAVIOLET SPECTRUM AND ITS DISPERSION

http://arxiv.org/abs/1010.2211v1

This is a very important paper because the database of "local" Type Ia UV spectrum is very small; and there is considerable consternation about how to detangle evolutionary from selection effects in distant supernovae.

So how did Hubble do?


Restricting samples to those of similar phase and stretch, the mean UV spectrum agrees reasonably closely with that at intermediate redshift, although some differences are found in the metallic absorption features. A larger sample will determine whether these differences reflect possible sample biases or are a genuine evolutionary effect.

Metallicity is of major importance when you are talking about the brilliance of fireworks.


Equally important is that we observe a strong wavelength dependent scatter in the rest-frame UV spectra of our local sample, as noted in E08. Independent of the calibration questions that have plagued recent photometric studies, the spectra demonstrate that the UV scatter is generic to SNe Ia over a wide range of cosmic time and is not likely an evolutionary effect. Much of this behavior can be attributed to the varying absorption line strengths of intermediate mass elements occupying the UV wavelength region, supporting the notion that the UV scatter arises from compositional differences between events.


Ok, so this is more of a weather report than a definitive paper; but at least they are trying to nail down whether or not our 'standard candles' are primary standards.

Jerry
2010-Oct-16, 04:27 AM
A Mismatch in the Ultraviolet Spectra between Low-Redshift and Intermediate-Redshift Type Ia Supernovae as a Possible Solution to the U-Band Anomaly


Comparison of composite spectra constructed from a subsample of 17 high-quality spectra to those created from a low-redshift sample with otherwise similar properties shows that the Keck/SDSS objects have, on average, extremely similar rest-frame optical spectra but show a UV flux excess. This observation is confirmed by comparing synthesized broad-band colors of the individual spectra, showing a difference in mean colors at the 2.4-4.4 sigma level for various UV colors. We further see a slight difference in the UV spectral shape between objects with low-mass and high-mass host galaxies. Additionally, we detect a relationship between UV slope and peak luminosity that differs from that observed at low redshift. We find that objects with this UV excess will have their distances underestimated by ~0.1 mag if the incorrect SED is used for calibration. This effect only occurs when the data probe the rest-frame UV. The recently discovered "U-band anomaly," which is currently the largest systematic uncertainty in SN Ia cosmology and results in a large systematic shift in the dark energy equation-of-state parameter, has the same observational qualities as this effect

Only 0.1 mag? If the spectra are brighter in the UV region all bets are off - How can they assume the punitive sample at higher redshift are not more like the local events observed that are brighter in the UV and a full magnitude or more brigher in the composite spectrum, locally?



We suggest that this discrepancy could be the result of differences in the host-galaxy population of the two SN samples.
I respectfully suggest the distant sample is heavily contaminated with very bright events. As always, when we first identify objects that are very distant, we should assume they are more likely representitive of the brightest of the events we observe locally. The supernova aging challenge chronicled above (in this thread) demonstrates that it is difficult to discriminate sub-types of supernova when the signal-to-noise ratio is bad.

Jerry
2010-Oct-22, 03:01 AM
http://arxiv.org/abs/1010.4040v2

Anotber paper,

Another new data reduction methodology. In this case, virtually unavoidable because the band width of the lightcurves has been extended. This paper primarily describes the methodology, but there are a few interesting observations:


The construction of the light-curve templates, which represent some average behavior of a sample of SNe Ia, has also revealed that at longer wavelengths, there is a marked increase in the SN-to-SN variation in light-curve behavior, even at a given decline rate.

Interesting, because other authors have concluded 'supernova are excellent standard candles, in the infrared.'


Tentatively, it also seems that the peak of the light curves show the least dispersion as standardizable candles. This poses a challenge for the observer, as SN events are typically “triggered” in the optical bands and the light curves peak earlier in the NIR. It is therefore often necessary to use template light curves to extrapolate the peak magnitude. On one hand, the increased dispersion in light-curve behavior will make this extrapolation more uncertain in the NIR. At the same time, these variations hint that another light-curve parameter might be at work and that this parameter may be correlated with residuals in the Hubble diagram.

Again, quite a contrast to earlier papers, where single parameter 'stretch' curve fitting resulted in no residuals when correlated with the Hubble diagram. If another light-curve parameter runs counter to expectations, what could it be?

Stay tuned....

Jerry
2010-Oct-27, 06:34 AM
http://arxiv.org/abs/1010.5272



Observational astronomy has shown significant growth over the last decade and made important contributions to cosmology. A major paradigm shift in cosmology was brought about by the observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although the supernovae data-sets of high quality are being produced, their statistical analysis leaves much to be desired. Instead of using the data to test the model directly, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.

I couldn't have said it any better myself...in fact, I couldn't say it this well...but you already knew that:)

Case in-point is this new paper: http://arxiv.org/abs/1010.4743

The Supernova Legacy Survey 3-year sample: Type Ia Supernovae photometric distances and cosmological constraints

The tables are stripped of parameters useful for statistical studies of type Ia demographics, such as the lost of one magnitude in blue factor.

AdamL
2010-Oct-27, 11:49 AM
Yeah, that is all well and good. But according to our Celestial Mechanic's infallible logic that last paper must be discarded because they used "paradigm shift" and it must therefor be inherently unscientific.
And that in the 2nd sentence of your quote! Shame on you, Jerry!

Jerry
2010-Oct-28, 04:07 AM
Paradyne???????????

Adams right - one must always avoid the p word. That's the gospel truth.

Celestial Mechanic
2010-Oct-28, 04:19 AM
Yeah, that is all well and good. But according to our Celestial Mechanic's infallible logic that last paper must be discarded because they used "paradigm shift" and it must therefor be inherently unscientific. And that in the 2nd sentence of your quote! Shame on you, Jerry!I have always respected Narlikar even though I don't often agree with him. I'm disappointed that he fell into the trap of using the "PS phrase". He should know better than that, but I'll continue to respect him. :)

Jerry
2010-Oct-28, 09:37 PM
You have to cut them a little slack, because they are concerned that the p-word shift might be in the wrong direction.

Narlikar & Vishwakarma's critic of the emphasis of many papers on SN1a is valid: Nobody should be assuming the final word is in on Dark Energy while there is a hanging question on whether or not the proper intepretation of the data is to contain it within the alpha cosmology model.

***

Here is another new paper with emphasis on cosmology curve fitting:

The Supernova Legacy Survey 3-year sample: Type Ia Supernovae
photometric distances and cosmological constraints

http://arxiv.org/abs/1010.4743v1

Here is a part that interests me:


In theMLCS2k2 approach, a prior is used that forces the extinction AV to be positive. This is equivalent to applying a prior on colour excess. However, since there is no evidence that the observed variation of SNe Ia colours is entirely and solely due to extinction by dust, applying such a prior is not justified.

I agree to a point. In an analytical chemical lab, the result is generally forced to zero because less-than-zero quantities are nonsense. You can either clip the data, or run the error bar positive - I don't know that there is a hard formal rule.

Less-than-zero dust is also nonsensical, so you have to ask the question: Why is the color excess such that it shows up on the charts as less than zero dust? In a chem lab, this generally occurs when there is a competing parametric or a baseline shift that has been over-compensated for. What parameter might be wrong?

I have attached a jpg with four graphs derived from the Guy paper; plotting redshift against the color (The bottom two plots, Salt Color and Sifto Color). Notice that the color is driven "less reddened" with increasing distance. It is unphysical to expect less total dust extinction with increasing redshift, so something is screwing up the color.

Generally relativity shares parametric space with dust extinction - that is, the GR correction factor looks a lot like dust extinction. If the GR correction is too large, the room for a dust correction gets smaller. Think about that.