Standard candle - in question - affects distance estimates

[wabbit]

OK you re saying that some interpretations of Ptolemy's model were wrong, or leading to dead ends. No quarrel about that, in a way it s similar to saying that the ether interpretation of the Lorentz transformation was wrong - certainly it looks to me like it obscured simple facts.

I don't think that the ancient Greeks held that the Earth was stationary ar the center of the universe, I believe there was a range of views then (Aristarchus of Samos is reported as a proponent of heliocentrism for instance but he was by no means the only one), debates about them, and probably the awareness at least for some that they just didnt have enough data to know for sure. I don't know on the other hand if the idea that the universe has no center at all was proposed then.

Back to the topic of this thread - if we have alternate models and they fit the data better, wonderful. Modern cosmology is a young science, and despite amazing advances in such a short time, it is unlikely to be complete - and perhaps it even took a wrong turn as you seem to suggest (some may not see DM and even less a CC as indicative of that but the data will sort it out), in which case it will still leave at least the legacy of great data to be reworked under new assumptions - time will tell, and I sure don't have the expertise required to foresee what it will tell.

 

[Garth]

This paper is pertinent to this thread: Theoretical uncertainties of the type Ia supernova rate, especially figure 15 on page 19.

7.5. Outlook
Our models indicate that the progenitor evolution of SNe Ia does not consist of one evolutionary channel, but has many different branches with the relevance of each depending on different aspects of binary evolution.With upcoming supernova surveys we will get more detailed information on the differences between individual SNe Ia. Therefore it is possible to gain insight in the sub-populations of SNe Ia. As a next step the characteristics of newly proposed progenitor channels should be investigated in more detail, including the properties of the merger products or the remaining companion stars. The outcome of such a study, combined with the results of this paper, can be linked with the different sub-populations of SNe Ia. However,when studying the rates of the other progenitor channels the uncertainties discussed in this work should always be kept in mind.

We wait for those upcoming supernova surveys!

Garth

 

[wabbit]

This paper is pertinent to this thread: Theoretical uncertainties of the type Ia supernova rate, especially figure 15 on page 19.

We wait for those upcoming supernova surveys!

So it is not feasible in the meantime to identify subtly different signatures that would be detectable in the data available from existing surveys, using multiple spectra captured over a decay curve ? I was sort of expecting such a kind of reestimation might provide at least a first go at the correction implied by such models, but this may have been overly optimistic.

 

[Garth]

So it is not feasible in the meantime to identify subtly different signatures that would be detectable in the data available from existing surveys, using multiple spectra captured over a decay curve ? I was sort of expecting such a kind of reestimation might provide at least a first go at the correction implied by such models, but this may have been overly optimistic.

That paper was on the errors in the SNe 1a formation rate - so its going to be complicated and messy.

My point has always been that the simple assumption that Type 1a SNe are standard candles over cosmological time scales (z=1 and beyond) is naive.

Garth

 

[wabbit]

Right, my assumption was that some signature might allow to isolate the separate channels. This is what they appear to suggest in

As a next step the characteristics of newly proposed progenitor channels should be investigated in more detail, including the properties of the merger products or the remaining companion stars

Then the qestion is whether existing surveys did capture enough data to identify this signature, and proceed from there, or whether these leave too much uncertainty and new surveys are required to sort things out. From what you're saying the latter appears to be more likely.

In any case, as I understand it if different channels estimated separately then yield the same distance/redshift curve this would corroborate the existing (LCDM) model, while different curves for different channels would require some explanation.

 

[Garth]

In any case, as I understand it if different channels estimated separately then yield the same distance/redshift curve this would corroborate the existing (LCDM) model, while different curves for different channels would require some explanation.

Agreed

 

[Ken G]

My point has always been that the simple assumption that Type 1a SNe are standard candles over cosmological time scales (z=1 and beyond) is naive.

And my point was that the naivete appears only when we expect an overly broad class of objects to be standard candles, when in fact it is only the appropriate subgroups that are standard candles. The trick is to have enough observed features to tell which standard candle they are. I'm interpreting the new information as saying you cannot any more just go with the light curve in one passband, or maybe even the light curve in all available passbands, you need more complete spectral information. So the question for now is, if we throw out all the observations that are not sufficiently constrained to be used as standard candles, do enough datapoints remain to still see evidence for acceleration, and is the acceleration still consistent with a cosmological constant equation of state? Or is it impossible to cull the subgroups, and all we can do is estimate and correct for their relative populations hidden in the data, and then can we still conclude the results are consistent with a cosmological constant? That would seem to be possible to address with current data, because if the answer is "we don't yet have a dataset like that, we need new observations that can constrain these subgroups", then it would seem the recent claims of "precision cosmology", and the Nobel prize associated with it, are all premature.

 

[Garth]

Yes, as we have yet to do that analysis of the SNe 1a spectral classes and compare them with the gold data set, then the present assumption that they are standard candles, and hence the deduction about the amount of DE, is naive.

The situation hasn't changed since 1998 when DE, and the \LambdaCDM model, based on them being standard candles was introduced, although a lot more information has come to light

Garth

 

[|Glitch|]

Yes, as we have yet to do that analysis of the SNe 1a spectral classes and compare them with the gold data set, then the present assumption that they are standard candles, and hence the deduction about the amount of DE, is naive.

The situation hasn't changed since 1998 when DE, and the \LambdaCDM model, based on them being standard candles was introduced, although a lot more information has come to light

Garth

What is especially disturbing is that even armed with the knowledge that there are different species of Type 1a SNe that produce different absolute magnitudes, nobody seems to care. There are currently 6,513 supernovae listed in Harvard's database, and the Type 1a SNe discovered after 2007 were identified using SNID software developed by Stéphane Blondin and John L. Tonry, which used the correlation techniques published in 1979. So the software will not be able to distinguish between a sub-Chandrasekhar, a Chandrasekhar, and a super-Chandrasekhar Type 1a SNe, yet it continues to be used.

Sources:
List of Supernovae - IAU Central Bureau for Astronomical Telegrams
Supernova Identification - Copyright © 1999-2007 Stéphane Blondin and John L. Tonry
http://[URL ']A survey of galaxy redshifts - [/URL]Astronomical Journal, vol. 84, Oct. 1979, p. 1511-1525.

 

[wabbit]

@|Glitch| - This seems quite serious, if I understand correctly what you are saying, this would seem to imply at best serious negligence in a lot of published studies. Am I misunderstanding you ?

To clarify, could you confirm whether and how you see the issue you refer to applying for instance in following :
The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample, Suzuki & al.

- or in other specific cases ?

Thanks

 

[Chronos]

The original supernova data still look solid to me. There is no evidence of faults in the data, or error bars. Science is constrained by data, not fairies. While that does not eliminate the possibility of error, it does limit the parameter space.

 

[|Glitch|]

@|Glitch| - This seems quite serious, if I understand correctly what you are saying, this would seem to imply at best serious negligence in a lot of published studies. Am I misunderstanding you ?

To clarify, could you confirm whether and how you see the issue you refer to applying for instance in following :
The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample, Suzuki & al.

- or in other specific cases ?

Thanks

It is certainly not negligence in any of the published studies before the different types of Type 1a SNe were known. They were written with the best information available at the time. However, that changed after 2006.

The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star.

The accelerating expansion of the Universe, and the need for dark energy, were inferred from observations of type Ia supernovae. There is a consensus that type Ia supernovae are thermonuclear explosions that destroy carbon-oxygen white dwarf stars that have accreted matter from a companion star, although the nature of this companion remains uncertain. These supernovae are thought to be reliable distance indicators because they have a standard amount of fuel and a uniform trigger: they are predicted to explode when the mass of the white dwarf nears the Chandrasekhar mass of 1.4 solar masses (M(o)). Here we show that the high-redshift supernova SNLS-03D3bb has an exceptionally high luminosity and low kinetic energy that both imply a super-Chandrasekhar-mass progenitor. Super-Chandrasekhar-mass supernovae should occur preferentially in a young stellar population, so this may provide an explanation for the observed trend that overluminous type Ia supernovae occur only in 'young' environments. As this supernova does not obey the relations that allow type Ia supernovae to be calibrated as standard candles, and as no counterparts have been found at low redshift, future cosmology studies will have to consider possible contamination from such events.

The paper in which you refer merely assumes that all SNe z > ~0.9 are Type 1a. An erroneous assumption at that. They should have known that they could be including super-Chandrasekhar Type 1a SNe in their data and taken measures to ensure that was not the case.

At z > ~0.9, any SN bright enough to be detected is overwhelmingly likely to be Type Ia due to the faintness of core-collapse SNe relative to SNe Ia (e.g., Dahlen et al. 2004; Li et al. 2011; Meyers et al. 2011). Furthermore, while “probable” candidates are not as certain as “secure” candidates, this is still a fairly high-confidence type determination: A “probable” SN Ia means that a SN Ia light curve template has a χ² P-value that is 10³ times larger than any SN CC value.

The three SNe that are z < 1 listed as "secure" in the paper you presented, had their light curves spectroscopically confirmed, but they did not measure the blue shift of the ejecta. That would have determined whether the SN was a Type 1a or Type 1ax. All Type 1ax SNe have a relatively low ejecta velocity (|v| < 8,000 km/s⁻¹) when compared to Type 1a SN (|v| > ~10,000 km/s⁻¹).

As a result, we have no way of knowing whether the Type 1a SNe used in the paper you referenced are sub-Chandrasekhar, Chandrasekhar, or super-Chandrasekhar Type 1a SNe. There simply is not information to draw a conclusion either way.

Sources:
http://www.nature.com/nature/journal/v443/n7109/full/nature05103.html - Nature 443, 308-311 (21 September 2006) | doi:10.1038/nature05103; Received 7 April 2006; Accepted 18 July 2006 (paid subscription) - arXiv Reprint
The Hubble Space Telescope Cluster Supernova Survey: VI. The Volumetric Type Ia Supernova Rate - arXiv : 1110.6442 (Reprint).

 

[|Glitch|]

The original supernova data still look solid to me. There is no evidence of faults in the data, or error bars. Science is constrained by data, not fairies. While that does not eliminate the possibility of error, it does limit the parameter space.

The data they are collecting I am sure is "solid." I have no reason to doubt any of the data being presented. The problem is that they are not collecting enough data to be able to distinguish between sub-Chandrasekhar, Chandrasekhar, and super-Chandrasekhar Type 1a SNe. Until that changes, there is no such thing as a "standard candle" in cosmology.

 

[wabbit]

It is certainly not negligence in any of the published studies before the different types of Type 1a SNe were known. They were written with the best information available at the time. However, that changed after 2006.

The paper I am referring to is from 2011.

The paper in which you refer merely assumes that all SNe z > ~0.9 are Type 1a. An erroneous assumption at that. They should have known that they could be including super-Chandrasekhar Type 1a SNe in their data and taken measures to ensure that was not the case.

So either these distinctions are inconsequential for the specific results this study obtains, or you are in fact saying that this 2011 paper ignores well known and relevant results and uses wrong assumptions.

I do not have the expertise to evaluate your claims, but given their very strong nature I would think they should require strong evidence as well. I was unaware there was such doubt about the results of this and other collaborations.

Edit: to clarify - as I understand it, the existence of several types of supernova within the initial broad standard candle class is not in question, and is discussed in several of these studies. The issue is whether they disregarded known and relevant distinctions. Your last post appears to make the much less controversial claim that some distinctions could not be corrected with the existing data (up to now, not just from 2006) despite all best efforts to do so. This is very different and not what I refer to as your strong claims.

 

[|Glitch|]

The paper I am referring to is from 2011.

So either these distinctions are inconsequential for the specific results this study obtains, or you are in fact saying that this 2011 paper ignores well known and relevant results and uses wrong assumptions.

I do not have the expertise to evaluate your claims, but given their very strong nature I would think they should require strong evidence as well. I was unaware there was such doubt about the results of this and other collaborations.

Edit: to clarify - as I understand it, the existence of several types of supernova within the initial broad standard candle class is not in question, and is discussed in several of these studies. The issue is whether they disregarded known and relevant distinctions. Your last post appears to make the much less controversial claim that some distinctions could not be corrected with the existing data (up to now, not just from 2006) despite all best efforts to do so. This is very different and not what I refer to as your strong claims.

The 2011 paper was before the new classification of Type 1ax was created in 2013, so they had no reason to determine the blue-shift of the ejecta because they could not have known at the time there was a distinction. Hence, the data is incomplete which had absolutely nothing to do with negligence. However, they should have been aware that Type 1a SNe at z > ~1 may include super-Chandrasekhar Type 1a SNe and take steps to ensure those SNe did not contaminate their data, since the paper that identified the problem was published 5 years earlier.

 

[Ken G]

It certainly sounds like a re-investigation is needed, where the dataset is simply culled down to the number of Ia SNe that can be unambiguously distinguished from other subtypes, so as to be used as standard candles. A smaller sample of data without systematic errors might tell a clearer story than a broader set of data that includes an unknown contribution from systematic errors. I'm betting we will see something like that soon, given the new information about what is necessary to be able to restore confidence that systematic errors are not present.

 

[Dale]

Closed pending moderation. I need to have a mentor who knows this stuff look into this.