Talk:Eta Carinae/Archive 3

Archive 1

Archive 2

Archive 3

Pre-FAC checklist

• Colour indices, magnitudes, etc.

I've changed this. Feel free to adjust further or comment if you don't like it. Lithopsian (talk) 18:43, 28 May 2015 (UTC)

• Image shuffling. New starbox image? First lightcurve has been left in a precarious position. More images? Maybe do after finishing the text.

I think we have enough images maybe - yeah do text first Cas Liber (talk · contribs) 20:37, 27 May 2015 (UTC)

• Infra-red observations. Especially important for this star, but I'll have to read up a bit.

agree Cas Liber (talk ·

I think I'm done. Hard to know when to stop, but I've hopefully written something accessible instead of an undergraduate course of Eta Car IR studies. Lithopsian (talk) 22:58, 2 June 2015 (UTC)

As somebody who has never taken a formal astronomy course (yet), I can understand it just fine. StringTheory11 (t • c) 23:41, 2 June 2015 (UTC)

contribs) 20:37, 27 May 2015 (UTC)

• Starbox spectrum, still need to settle on a sufficiently vague and all-encompassing term. For that matter, other values like temperature and radius are equally poorly represented by either a single number or a range.

Well, "variable" it is, unless someone has a brainwave about how to express it better. Lithopsian (talk) 12:52, 31 May 2015 (UTC)

• Reword the radio stuff. Not my field, but shouldn't be too hard.

Well I reworded it, but comments elsewhere suggest it should be expanded. Lithopsian (talk) 18:43, 28 May 2015 (UTC)

I've expanded this a little. Maybe someone else can add even more. Lithopsian (talk) 18:43, 28 May 2015 (UTC)

• Final proof-read. It is getting hard for me to read with enough focus to spot the most obvious typos. Third pair of eyes needed? Or will it just come out in the review?

I'll find a someone good with prose who is a layperson and interested in clarity of prose at this point as they will be able to highlight accessibility issues. I know a couple of good people who'll be hard taskmasters. It would be prudent to do this before FAC in an article of this size. But will wait until content all sorted Cas Liber (talk · contribs) 20:37, 27 May 2015 (UTC)

Is there anything else? More about supernova imposters? More about the colliding winds? More about the spectroscopic events? More about the discovery of the binary companion? Lithopsian (talk) 18:59, 27 May 2015 (UTC)

I'd say - 'no', 'possibly', 'not sure too esoteric', and 'yes' respectively Cas Liber (talk · contribs) 20:37, 27 May 2015 (UTC)

I've added incidental mentions of the colliding winds and spectroscopic events, and might mention them again in the IR stuff. I've expanded the 20th century observations section to say a bit more about the binary discovery. Lithopsian (talk) 18:43, 28 May 2015 (UTC)

Casliber asked me to take a look. At this stage i've only read up to "surroundings". I expect this is all technically accurate, and pretty interesting, but it is also bordering on incomprehensible. There's a sh*tload of stuff happening in the Eta C system, and this article tends toward describing what is happening, but leaving the lay reader a bit in the dark because there's not enough text about what the science means. Here's an example of doing the right thing for the reader: "Further light echo observations show that following the peak brightness of the Great Eruption the spectrum developed prominent P Cygni profiles and CN molecular bands. These indicate that the star, or the expanding butt of ejected material, had cooled further and may have been colliding with circumstellar material in a similar way to a type IIn supernova". This is excellent; we just need more of these explanations i think.

• "...the periastron passage of the binary orbit". No-one will know what a periastron passage is - a wikilink would be essential at minimum, but given the importance of the topic (that is, why did Eta C have peaks several years apart), I think we need a plainer English explanation in the article text. BTW periastron is wikilinked twice later in the text, but to different terms each time! (peristron, and apsis)

On wikilinks, the recommendation is only ever to link the first occurrence of a term. However, I've tended to link the first occurrence in each "section" (not exactly rigorously, but where it seems useful). Some sections in this article are larger than many entire articles, and it seems a bit unhelpful to expect someone who comes along and clicks through to "Evolution" to have to read the previous 10,000 words to know what is going on. Don't want to just get the whole thing nixed at FA review though. Lithopsian (talk) 16:44, 31 May 2015 (UTC)

• "...this was Eta Carinae during its Great Outburst of in the 1840s" - the term Great Outburst (which sounds hilarious) has not been elsewhere used. I suggest stick to Great Eruption.

oops, my bad. changed. Cas Liber (talk · contribs) 12:11, 31 May 2015 (UTC)

• "...expelling material that formed the Little Homunculus and Weigelt Blobs". There is a difficulty with the historical section occasionally, as in this passage (and in the earlier references to ejection of dust), where references are made to things we haven't been told about. So far, all we have been told is that we are looking at a star of variable brightness, and then that this had something to do with dust. We have no idea what kind of things the Little Homunculus and Weigelt Blobs are, nor links to them. Is there any way that a version of the first paragraph under "properties" can become the first para of the body text? Just a thought.

I've just taken those terms out. They are barely described at all in this article. Actually, reading more, I've wiki-linked Weigelt Blob once later. More generally, the lead isn't huge and maybe there could be expanded a little if some context is needed. Lithopsian (talk) 13:36, 31 May 2015 (UTC)

• Under "visibility": how can a star possibly be "clearly non-stellar"?

It isn't a star :) We don't see a star (either of them), we only see a small blob of nebulosity. I've added cheap double-quotes to indicate this, but maybe there is a better way to structure the sentence. Lithopsian (talk) 13:36, 31 May 2015 (UTC)

• "...the extreme P Cygni star HDE 316285 (B0Ieq)". What does it mean for a star to be an extreme P Cygni type? What is the implication of this comparison (ie. the interesting information)

I've restructured (and linkified) the sentence to hopefully indicate what it means. Lithopsian (talk) 13:36, 31 May 2015 (UTC)

• "The spectrum is dominated by emission lines, usually broad although the higher excitation lines are overlaid by a narrow central component." What? I had no idea what this meant.The two sentences that follow have problems. Do we know what "high excitation" ionisation is? What is an "absorption wing"??

I've linked a number of terms, explained a few more. This is still going to be tough reading without a background understanding of astronomical spectra, but hopefully at least the links allow someone to gain the background. Lithopsian (talk) 13:36, 31 May 2015 (UTC)

• "...emission in both permitted and forbidden lines". Again, what? What on earth are permitted or forbidden lines? Is this an awkward translation of a foreign text? Are these synonyms for absorption and emission? All pretty confusing. The sentences about the hydrogen, helium and nitrogen lines were pretty clear, though.

"Permitted" and "forbidden" lines are standard terms in astronomical spectroscopy. "Forbidden" lines represent atomic transitions that are extremely rare under terrestrial conditions but more common in interstellar environments; the name comes from the fact that they were originally thought to be impossible since they never occurred in the laboratory. Conversely, "permitted" lines are transitions that can be observed under terrestrial conditions. For a more detailed account check out the historical "discovery" of "nebulium." — Preceding unsigned comment added by 128.114.22.81 (talk) 23:37, 3 June 2015 (UTC)

• an "accidental resonance"? sounds like something technological in nature (and pretty mysterious at that). Can we clarify?

Seems to have already been done by someone else. I've gone ahead and copyedited it, to make it sound less awkward, and clarified a point. StringTheory11 (t • c) 23:59, 2 June 2015 (UTC)

• italics are being used inconsistently toward the end of the spectrum section and in the one that follows.

I de-italicised - we'll either bluelink or explain... Cas Liber (talk · contribs) 12:19, 31 May 2015 (UTC)

• in the radio emission section, a new type of line, a recombination line, is introduced without either explanation or link. And then also added is "continuum emission" again without explanation.

Couldn't find wikilinks for these terms, so added parentheses with explanation. Lithopsian (talk) 12:58, 31 May 2015 (UTC)

I've gone ahead and added a redlink to the term. I'll probably go through this article and add some more redlinks to terms that should have their articles, to encourage article creation. StringTheory11 (t • c) 23:52, 2 June 2015 (UTC)

Thanks for the hard work on this everyone. hamiltonstone (talk) 11:41, 31 May 2015 (UTC)

This is good stuff, exactly what we need. I can't see the wood for the trees after reading the article so often. Plus I know what "P Cygni profile" and "accidental resonance" mean, and assume the rest of the world must too ;) Lithopsian (talk) 13:40, 31 May 2015 (UTC)

Possible effects of supernova on earth??

Nearly everything in this section is irrelevant, beginning at "At least one paper has projected...". No real point in describing the effects various potential supernovae would have on earth if they were to occur ~10-100x closer to earth than Eta Carinae. It's totally interesting and presumably is discussed in an article of its own, but doesn't add anything to this article aside from confusion. Spameroo (talk) 16:47, 18 March 2016 (UTC)

The best place for generic discussion of the effects of a supernova on Earth would be in supernova. It has such a section already. There is also Near-Earth supernova, rather fancifully rated as a class B article, if you really want to go into it in depth. This article only needs to discuss information specific to Eta Carinae and enough background to put it in context. Eta Carinae is a fascinating star and it will explode one day, but I wouldn't be putting money on it going soon. There are good reasons to think it has a significant amount of evolution to go through before it is ready. It may well not even have started core helium burning yet, let alone finished it and gone through to an iron core. Part of the excitement is the idea that it could produce a superluminous supernova. I've already tried to damp down the hyper with realistic caveats about what Eta Carinae is likely to do and when, but I'm told Wikipedia articles can always be improved ... Lithopsian (talk) 20:45, 18 March 2016 (UTC)

@Spameroo:, generally articles have some overlap to give any given article some context. There is always alot of buzz about Betelgeuse and Eta Carinae going supernova so better to have some coherent and sourced material as it will be added willly-nilly otherwise...Cas Liber (talk · contribs) 21:08, 18 March 2016 (UTC)

New Mass Model for Eta Carinae

According to the source given for the mass values of the system, , it states that their preferred model of the system has the mass value of Eta Carinae A at 200 M_☉ and Eta Carinae B at 80 M_☉. They state in the article, and I quote, "We therefore conclude that in order to get a good fit for the GE, mass transfer must be taken into account, and that the two stars of η Car are much more massive than usually thought." But not only this. The article also states, "We used two models. Model "MTz" assumes (wrongly) that the secondary is not evolved, and we took it to be a ZAMS star." This proves that the mass value of 170 M_☉ for the primary star is incorrect. The article also states,"We conclude that it is not possible, under our assumptions, to use a low-mass system of ~150 M_☉ to fit the rises in the light curve of the GE. This proves that according to their measurements, that the common model for the system is not massive enough to have caused as significant a change in the magnitude of the system during the Great Eruption. I would greatly appreciate if this information could be included in the article and the List of most massive stars article. I also appreciate the feedback from Lithopsian and Tarlneustaedter. Thanks.

Comment By:174.110.102.238- 00:35, 19 March 2016 (UTC).

Glancing through the article, it appears to be an interesting analysis, but (from my perspective), far from definitive. The article derives different masses than other approaches have, but that does not invalidate the other approaches - it simply accentuates the uncertainty. At this point, I'd suggest that the range 120-200 is probably still appropriate. I would not even put 200 as the most likely value. Regards, Tarl.Neustaedter (talk)

I agree. It is highly speculative at this point, and basically not confirmed by any other research. Of course much about Eta Carinae is highly speculative, but when broadly the same model is supported by a range of researchers then we can state it as (for now) "fact". Even the Kashi-Soker papers refer to it as the Standard Model. At the very least, we should present the standard model as having an equal weighting to the new model. Given that a range of more recent papers essentially gloss over the Kashi-Soker models and keep quoting the standard model, I think it would be quite justifiable to drop the high mass values from the starbox altogether and just mention them in the text. They might be the "preferred" model of one research team, but certainly not of the wider astronomical research community. Lithopsian (talk) 15:29, 20 March 2016 (UTC)

Oh, and I moved this article to the end of the talk page so it could be found. When talk page comments are added, it's customary to create new sections at the bottom of the page - see the "new section" link at the top of the talk page. Regards, Tarl.Neustaedter (talk) 01:32, 19 March 2016 (UTC)

References

Time to describe the mechanism of the Great Eruption?

The article currently describes observations of the Great Eruption, but says little to nothing about what caused it. If I remember rightly, this was done simply because we don't know what caused it, but there are now at least three models and it may be worth describing them. The "classic" model is simply a super-Eddington wind which is effectively a larger version of more normal LBV instabilities. This has looked progressively less and less likely as the scale of the eruption has been determined. The mass transfer model is basically the release of gravitational potential energy from primary wind material accreted onto the secondary, triggered by a combination of LBV-type expansion of the primary and orbital interaction with the secondary. Another model is the "explosive" model where a sub-supernova scale explosive event ejects a substantial fraction of the star, with the high luminosity caused by conversion of the kinetic energy to radiation in the same way as type IIn supernova, basically colliding with previously ejected circumstellar material. Yes? No? Did I miss anything? Lithopsian (talk) 17:48, 20 March 2016 (UTC)

@Lithopsian: I think some note would be good to add. Cas Liber (talk · contribs) 21:17, 4 September 2016 (UTC)

New high-res images of the star's disk

http://www.space.com/34445-eta-carinae-explosive-star-system-best-views.html

--101.161.174.247 (talk) 07:35, 21 October 2016 (UTC)

Where was the Great Eruption?

In the lead paragraph, you mention "the Great Eruption" in the mid-1800's. To novices like myself, our first guess would be that the Great Eruption spanned many star systems and thus a fair extent of the night sky. It's only further down in section 1.2 that we find out that the Great Eruption wasn't all that great and only describes events happening within Eta Carinae, with its extreme increase in magnitude.

Maybe you could substitute the following unlined passage in the second sentence of the article: First recorded as a 4th-magnitude star, it brightened in 1837 until it outshined all but half a dozen of the brightest stars. This period, from 1837 to 1856, was known as the Great Eruption.

Just a suggestion. --RoyGoldsmith (talk) 18:11, 12 March 2017 (UTC)

I see nothing in the article to imply what you have imagined. η Car is consistently described as one star system from the lead onwards. Lithopsian (talk) 14:26, 24 March 2017 (UTC)

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luminosity and temperature during great eruption

Would it be a good idea to include the luminosity and temperature of Eta Carinae during the great eruption? — Preceding unsigned comment added by JayKayXD (talk • contribs) 21:03, 22 April 2019 (UTC)

They're not well-known. Also variable, obviously, since the eruption lasted for many years. It would be mis-leading to put some specific numbers in the starbox. There are estimates, and some are discussed in the text. If you can find reliable references then they can also be discussed. Lithopsian (talk) 15:58, 23 April 2019 (UTC)

The radius of Eta Carinae is mentioned as 1400 R_☉ during the great eruption in the size section of this Wikipedia article. so if it maintained it's luminosity of ~5x10^6 L_☉ then the using the Stefan-Boltzmann law would result in Eta Carinae's temperature being ~7300K during the great eruption. https://iopscience.iop.org/article/10.1088/2041-8205/709/1/L11 I also found this which suggests that Eta Carinae's temperature was ~7500K during the great eruption.JayKayXD (talk) 04:43, 27 April 2019 (UTC)

We don't know its temperature, although light echoes suggest it was cooler than that. Its eruption luminosity was considerably higher than it is now, but we don't really know how much, just a lower limit based on the visual brightness. And before you do too much original research, a huge proportion of its current luminosity is in the infrared, so the visual magnitude isn't a good starting point for calculations. Lithopsian (talk) 13:03, 28 April 2019 (UTC)

How much cooler? I don't think it would've been less than 6000K, although it was described as "color and size very like Arcturus" which suggests it would've been likely orange during the great eruption leading to the 4000-5000K range but that means it probably would've had to have been at least 3000 R_☉ which seems extremely dubious for even a red supergiant star, let alone a star like Eta Carinae so that seems really unlikely. JayKayXD (talk) 21:15, 29 April 2019 (UTC)

The light echoes suggest 5000 K. Take that with a pinch of salt though, and certainly don't compare it to a normal star. It was an eruption, not a star with a conventional photosphere. There would be no unambiguous position at which to declare the surface or radius. It is universally accepted that it was both cooler and more luminous during the great eruption than it is now, but more is hard to say because we don't really have a vaguest idea of the physical mechanism of the eruption. The temperature derived from the light echoes is based on comparison of particular spectral lines (in absorption, very weird for an eruption!) to those of conventional supergiants. The colour could have been quite different, possibly due to additional reddening from dust. Lithopsian (talk) 16:39, 30 April 2019 (UTC)

Thanks for the info. 5000 K to 7500 K seems like a reliable range for the temperature during the great eruption though I think I heard somewhere that it was 10800 K during the great eruption which seems too high but that could've been it's physical surface.JayKayXD (talk) 02:44, 1 May 2019 (UTC)

Also, light echo studies after the light curve peak show strong P Cygni profiles and CN Molecule bands suggesting 4,000-4,500 K.216.209.30.32 (talk) 22:28, 23 May 2019 (UTC)

Triple star system before GE?

I heard that Eta Carinae may have been a tripe star system before the GE:https://newatlas.com/eta-carinae-triple-star/55746/ . Should this be mentioned in the arcticle?JayKayXD (talk) 23:50, 13 June 2019 (UTC)

There is also a 2016 paper suggesting a binary merger in a (then) triple system. I think we should add something about this, even though both papers are highly speculative. There are also slightly older, equally speculative, papers about large-scale mass transfer causing the Great Eruption. The article implicitly refers to this without explaining it in great detail, probably giving it more credence than it deserves as a theory that didn't get picked up by the scientific community. The only problem I have with discussing these ideas is where to put them. There is an existing section about the Great Eruption but in the context of observations rather than what caused it. Of course we still don't really know what caused it, but perhaps the best way to get that across is a section explaining the various theories and why none of them quite work. Lithopsian (talk) 14:05, 14 June 2019 (UTC)

Sure. We could have an entire section on what caused the great eruption since there are more theories out there. The Smith 2011 ref explains another theory where the great eruption could work without a third star. In that theory, star A grows so large that it's even larger than the angular separation of it and star B meaning star B would've been inside star A's photosphere.JayKayXD (talk) 14:41, 16 June 2019 (UTC)

New Picture

The Hubble Telescope has given us a new image of Eta Carinae, with an ultraviolet capture of magnesium, rendered blue, on the previously ejected nitrogen, rendered red. I assumed a Hubble photograph would be free to all, but I can't pick it up to insert in our article. J S Ayer (talk) 21:56, 3 July 2019 (UTC)

Its already in the article. Lithopsian (talk) 13:29, 4 July 2019 (UTC)

Bolometric luminosity during great eruption?

What was the bolometric luminosity of the primary star in 1843? Do we even know if it changed in bolometric luminosity? Also, please don't use it's visual brightness in 1843 as at least a good fraction of the light was likely in infrared due to low temperatures of the primary and absorption from the ejected material. Anyway, if it didn't increase in boloemtric luminosity, what could've caused it to increase by over 4 magnitudes in brightness? 67.71.87.215 (talk) 05:51, 23 December 2019 (UTC)

It is generally assumed that the bolometric luminosity increased substantially during the Great Eruption, hard to account for even the visual brightness any other way. It has been estimated to be as high as 50 million L_☉, but without knowing the spectral energy distribution at the time it is hard to be accurate. More recent estimates have been somewhat lower. Extinction and recycling into the infrared probably weren't large until the ejecta cooled, although a G-type spectrum at the time indicates a pseudo-photosphere significantly cooler than the true surface of the star or even the apparent surface now. The switch from a B-type (-ish) temperature to a G-type temperature could account for 2-3 magnitudes of the visual brightness change. Lithopsian (talk) 14:47, 23 December 2019 (UTC)

I don't think 5,000 K is much closer to the visual spectra peak than 9,400 K. i do believe a good chunk of the increase in brightness came from bolometric luminosity but 50 million L_☉ seems too high.Is there anything else that could've contributed to the brightness increase?67.71.87.215 (talk) 18:13, 25 December 2019 (UTC)

There's so many things wrong woth that, I don't know where to start. Maybe stick to facts instead of trying to make stuff up. Perhaps even go read some of the papers linked in the article. Or even read the whole article, which discusses many of these things. There's enough out there to keep you busy for months. Then maybe start making stuff up ;) Lithopsian (talk) 16:07, 27 December 2019 (UTC)

surface gravity?

Mass loss section has this: Eta Carinae A is losing a lot of mass due to its extreme luminosity and relatively low surface gravity.
So, it is known it has 'relatively low' surface gravity. How much is it then? 109.240.251.13 (talk) 00:33, 9 October 2019 (UTC)

Need to define "surface" first. Lithopsian (talk) 14:45, 9 October 2019 (UTC)

Lithospan when people talk about Eta Carinae's surface, they usually mean the 9,400 K surface or the edge of the optically thick stellar wind.JayKayXD (talk) 02:16, 9 December 2019 (UTC)

Using the figures for η Car A in the infobox 200 M☉ and 240 R☉ and the formula

$g\propto {\frac {m}{r^{2}}}$

given in surface gravity gives 0.003 that of the Sun. Sun says the Sun's surface gravity is 28 times that on earth. If my sums are right (check, please) that should give a rough idea. Thincat (talk) 17:45, 31 December 2019 (UTC)

How large was Eta Car A during the peak of the GE?

What was the radius of this beast during the peak of the great eruption? This arcticle says 1,400 R_☉ but estimates of the temperature (5,000 K) and bolometric luminosity 50 million L_☉ during the peak of the GE suggest it was much larger. 142.112.185.194 (talk) 16:42, 24 March 2020 (UTC)

First, the size of an explosion, even a slow-motion explosion taking many years, isn't really defined. The article contains a value for the radius published by a professional astronomer in a peer-reviewed paper, even if it is sort of a meaningless hand-waving value. Taking a temperature from one paper and combining it with a luminosity from another paper is problematic at best. In this case, the luminosity is a bit of a ballpark figure although widely-accepted. However, the temperature is really nothing of the sort: 5,000 K is the (very) approximate effective temperature of a normal star having a spectrum of the same broad type as some observed light echoes from neat the peak of the Great Eruption. The paper itself makes it clear that this should not be considered the effective temperature of any sort of spherical object; the explosion was not spherical and the origin of the spectral lines is unlikely to be a black body in thermodynamic equilibrium.

Although published in a peer-reviewed paper, the value of 1,400 R_☉ is actually not the radius during the Great Eruption, partly because such a thing is not very meaningful and was not calculated in the paper. 1,400 R_☉ is an assumed radius during a typical LBV eruption that may have been taking place prior to the Great Eruption. The radius is calculated to show that the secondary star would have passed within the photosphere during periastron, potentially with a dramatic result. Possible the article text should be edited to make that clear. Lithopsian (talk) 20:17, 24 March 2020 (UTC)

A lot of those things you mentioned should be in the article.142.112.185.194 (talk) 02:01, 26 March 2020 (UTC)