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glappkaeft
2014-Jan-22, 11:18 AM
You heard it here first. According to a guy on a Swedish forum this would be the closest typ 1a Sn since SN 1937C so there should be a lot of interesting papers coming out!

Info at http://www.astronomerstelegram.org/?read=5786

NoisyAstronomer
2014-Jan-22, 01:33 PM
SQQQUUUEEEEEE!!!!! Oh I'm so excited about this. I couldn't sleep and checked twitter and I'm really glad I did.

Such a close SN1a is going to be great for looking at it in detail, which is nice since we use them as standard candles to measure distances out to several billion light years. AND get your backyard scopes ready... it hasn't hit peak brightness yet. I'm hearing estimated predictions up to magnitude 8? I'm sure the Virtual Star Party astronomers are all going to try for it (the northern hemisphere ones anyway.)

I rambled a bit about it here if you're interested: http://cosmoquest.org/x/blog/2014/01/supernova-alert/

Corrections welcome! I did write it in a bit of a rush with no caffeine, only astronomical excitement.

trinitree88
2014-Jan-22, 01:34 PM
You heard it here first. According to a guy on a Swedish forum this would be the closest typ 1a Sn since SN 1937C so there should be a lot of interesting papers coming out!

Info at http://www.astronomerstelegram.org/?read=5786

Thanks for that. Pretty close@ 11.8 lightyears. pete

The prompt neutrino burst should precede the light curve rise to maximum as the photosphere expands @a little less than c/10...20, 000 km/sec by the silicon lines, and the neutrinos travel @c. Might be hearing from the particle physicists in the next few hours. There were only about 11 from the IMB during SN1987a@ about 170, 000 lt years....so unless there's some beaming..might be pretty slim seeing in the tanks.

ngc3314
2014-Jan-22, 02:03 PM
Our local neutrino folks say detection sounds unlikely even if it turns out not to be a type Ia - the Cerenkov experiments aren't very sensitive to SN neutrinos (i.e. would see only within the Local Group), and this is a lot farther away than SN 1987A. Also, they're not grinning and gyrating. But I haven't seen anything official from the solar neutrino detectors, which would probe the right energies for SN.

(But if there were to be a detection - the coolness! The coolness!)

trinitree88
2014-Jan-22, 02:24 PM
Our local neutrino folks say detection sounds unlikely even if it turns out not to be a type Ia - the Cerenkov experiments aren't very sensitive to SN neutrinos (i.e. would see only within the Local Group), and this is a lot farther away than SN 1987A. Also, they're not grinning and gyrating. But I haven't seen anything official from the solar neutrino detectors, which would probe the right energies for SN.

(But if there were to be a detection - the coolness! The coolness!)


I just checked the range of the LIGO experiments @ Living Ligo,...and it can vary depending upon local seismic background, but it's not inconceivable if we have a double degenerate precursor ( two inspiraling white dwarves, neutron stars, or one of each) that a gravitational wave may be seen here for the first time @LIGO. Max range out to about 20 Mparsecs...more typical about 15 Mparsecs. ....thats about 4 times M82. Pete

I'll go out on my standard limb and predict a successful detection of a gravitational wave from this event...hot fudge sundae..three scoops of ice cream on it. Betting individuals stand up?...lol.

The Frozen One
2014-Jan-22, 02:25 PM
Awesome! Thanks for sharing this. I think tonight is a good night to bring out my telescope... if atmospheric conditions permit. Hopefully I'll get a glimpse of it.

antoniseb
2014-Jan-22, 03:37 PM
I just checked the range of the LIGO experiments @ Living Ligo,...and it can vary depending upon local seismic background, but it's not inconceivable if we have a double degenerate precursor ( two inspiraling white dwarves, neutron stars, or one of each) that a gravitational wave may be seen here for the first time @LIGO. Max range out to about 20 Mparsecs...more typical about 15 Mparsecs. ....thats about 4 times M82. ...
I suspect that since the diameter of White Dwarfs is about Earth-sized that LIGO and VIRGO will not be especially sensitive to this event. Two inspiralling Neutron Stars yes, but White Dwarfs, I'm guessing not.

litespeed
2014-Jan-22, 07:33 PM
http://io9.com/a-white-dwarf-just-exploded-creating-the-closest-super-1506539405?utm_campaign=socialflow_io9_facebook&utm_source=io9_facebook&utm_medium=socialflow

Who would have seen it coming.

NEOWatcher
2014-Jan-22, 07:45 PM
pfffft. Old news. It happened 12 million years ago.

On the serious side, I can't wait to hear details on what this reveals.

Swift
2014-Jan-22, 07:49 PM
I've merged the thread from Astronomy Activism into the already existing thread in the Astronomy forum

Jerry
2014-Jan-22, 08:45 PM
I just checked the range of the LIGO experiments @ Living Ligo,...and it can vary depending upon local seismic background, but it's not inconceivable if we have a double degenerate precursor ( two inspiraling white dwarves, neutron stars, or one of each) that a gravitational wave may be seen here for the first time @LIGO. Max range out to about 20 Mparsecs...more typical about 15 Mparsecs. ....thats about 4 times M82. Pete

I'll go out on my standard limb and predict a successful detection of a gravitational wave from this event...hot fudge sundae..three scoops of ice cream on it. Betting individuals stand up?...lol....and I will go out on the same limb, and predict a non-event; in full agreement with you; in that this should yield an affirming result if it is a a double degenerate source and the theory behind your prediction is correct.

NoisyAstronomer
2014-Jan-22, 09:19 PM
Thanks, Swift! Yeah, sad if no neutrinos, but there will still be plenty to see.


Sent from my iPad using Tapatalk

trinitree88
2014-Jan-22, 09:38 PM
Thanks, Swift! Yeah, sad if no neutrinos, but there will still be plenty to see.


Sent from my iPad using Tapatalk

Noisy. At 11.8 million lightyears, our new baby supe is 70 times further away than the Large Magellanic Cloud, home to Sn1987A. So inverse square law for an isotropic spallation of neutrinos gives about a 1/500 chance of seeing one, other things being equal.

Don Alexander
2014-Jan-23, 05:26 AM
This is what I get for not starting the "You heard it here first!" thread - someone else does it! ;)

Quite a pity this one was discovered so late!! Yes, late. It's already visible on precovery images on the 15th at mag ~14.4, and was not reported until about five days later. That likely makes it somewhat less interesting scientifically than SN 2011fe was. I guess the bright galactic background was to blame, hard to see a new faint point of light sitting right on a high-surface brightness galaxy.

Concerning distance, seems this is the closest one since SN 1993J in the very neaby M81.

I'm actually unsure what the neutrino signal of a Type Ia would even be. Core-collapse SN neutrinos are produced mostly by Electron-Proton merging afaik, you don't get that here.

The possible inspiral GW signal is worth searching for, though.

According to the spectroscopic classification, it's reddened, so it will not be quite as bright as it could have become.

Lastly, weird that we get a Type Ia in a starburst galaxy. ;)

StupendousMan
2014-Jan-23, 12:19 PM
The CalTech guys have compared a Keck image of the SN and its surroundings to archival HST images of M82. They see no sign of a progenitor in the HST images -- and one would NOT expect to see any sign of one, if the progenitor is either a double degenerate or single-degenerate systems with main-sequence companion.

Check it out:

http://www.astronomerstelegram.org/?read=5789

Don Alexander
2014-Jan-23, 10:49 PM
Some updates:

- The SN progenitor is undetected in very deep stacks of X-ray observations by Chandra: http://www.astronomerstelegram.org/?read=5798, http://www.astronomerstelegram.org/?read=5799

- The SN itself is undetected in radio and sub-mm observations, this is typical for SNe Ia: http://www.astronomerstelegram.org/?read=5800

- Hi-res spectroscopy indicates the extinction along the line of sight is quite high, E(B-V) > 1: http://www.astronomerstelegram.org/?read=5797 This roughly implies at least 3 mags in the R band!! Therefore, if it were not reddened, it would actually be 8th magnitude now! I think the initial estimates of it rising to 8th were based on an erroneous assumption of the explosion date. We now know it detonated somewhere between the 13th (deep non-detection by MASTER: http://www.astronomerstelegram.org/?read=5795) and the 15th (first reported detections (so far) at about 14.5 mag), so it was already six days old when it was announced. Therefore, it likely has not much more to rise. i'm not totally familiar with SNe Ia light curves, but I don't think it's going to be more than one magnitude. So in the end, it will actuall be a bit fainter than SN 2011fe, probably.

Swift
2014-Jan-24, 03:14 PM
Spaceweather.com has a gallery of submitted amateur images (http://spaceweathergallery.com/index.php?title=nova)

NoisyAstronomer
2014-Jan-24, 11:01 PM
Noisy. At 11.8 million lightyears, our new baby supe is 70 times further away than the Large Magellanic Cloud, home to Sn1987A. So inverse square law for an isotropic spallation of neutrinos gives about a 1/500 chance of seeing one, other things being equal.

What I meant was plenty to see in the electromagnetic spectrum :-)

Don Alexander
2014-Jan-28, 09:08 AM
http://astro.berkeley.edu/bait/public_html/2014/sn2014J.html

Or: "The undergrads messed it up"

Poor undergrads. :(

Jerry
2014-Jan-28, 03:36 PM
I have written similar filtering software. It is most difficult to discriminate when the images are noisy in the 'business' bandwidth. The deep reddening would have made finding the peak difficult for search algorithyms, even though it becomes painfully obvious after massaging.

Tough for the grad students indeed - nothing worse than missing the opportunity of a lifetime.

trinitree88
2014-Jan-28, 08:12 PM
snippet...."Tough for the grad students indeed - nothing worse than missing the opportunity of a lifetime."

Jerry. Yep. When Lee and Yang proposed that maybe parity was not conserved in the weak interaction (Tau,Theta decays)...they didn't know that not only had it been seen in dozens of experimental sets of data....it had been seen in every run of every set of data where it could have been seen. Nobody had ever looked for it.:doh:

pete

Jerry
2014-Feb-13, 04:05 PM
http://arxiv.org/abs/1402.2896 Upper limits on the luminosity of the progenitor of type Ia supernova SN2014J

The authors are all-but ruling-out the classic degenerate white dwarf accreting matter to the Chandrasahkar limit as the source of supernova SN2014J. This theory has been kept alive by assuming most event were consistent with this model; and only rarely are supernova the product of a collision of a pair of white dwarfs. Now we have to wonder if it is white dwarfs at all, and we have completely whiffed on causality.

Amber Robot
2014-Feb-13, 07:25 PM
http://arxiv.org/abs/1402.2896 Upper limits on the luminosity of the progenitor of type Ia supernova SN2014J

The authors are all-but ruling-out the classic degenerate white dwarf accreting matter to the Chandrasahkar limit as the source of supernova SN2014J. This theory has been kept alive by assuming most event were consistent with this model; and only rarely are supernova the product of a collision of a pair of white dwarfs. Now we have to wonder if it is white dwarfs at all, and we have completely whiffed on causality.

For the record (in case you don't want to click on this link and read through the paper) here's what they say:


Our results firmly rule out the progenitor being a single-degenerate system with a photospheric radius comparable to the near-Chandrasekhar mass white dwarf radius and mass accretion rate in the range where stable nuclear burning can occur.

Don Alexander
2014-Feb-14, 11:30 AM
So, it's ruled out in ONE case. How does that lead to "we have to wonder if it is white dwarfs at all"?? :confused:

Jerry
2014-Feb-16, 10:36 PM
So, it's ruled out in ONE case. How does that lead to "we have to wonder if it is white dwarfs at all"?? :confused:
One nil result can null a hypothesis.

We have observed thousands of type 'Ia' events, and we have a good knowledge of the spectral signature, light curve, magnitude and expansion characteristics. This is the closest type 'Ia' event we have observed; and it is pretty much textbook in terms of all of the observed characteristics thus far. If the theory these events are caused by exploding white dwarfs with 1.4 solar masses is true; we should see such a star in the exact proximity of the event before it occurred. We don't; and in this case, this expected precursor is ruled-out with significant observational limits.

It is a more reasonable assumption that we do not know what the precursor of supernova 'Ia' events is, than it is to assume that this nearest event is a magical exception. It is time to search the same space for other possible precursor candidate. (It is too bad the event is highly reddened; this will limit the search.)

The 'white dwarf precursor' hypothesis has never been anything more than an educated guess; and it is not there.

Schneibster
2014-Feb-16, 10:43 PM
Jerry, you've made a logical error.

You're assuming that because this event didn't have the single-dwarf hypothesis as a progenitor, no event has it as a progenitor. That's a non sequitur; literally, "it does not follow."

OTOH, I agree they should look for another precursor or progenitor. And I would guess that statement in their paper was intended to say exactly that.

antoniseb
2014-Feb-16, 11:57 PM
Jerry, you've made a logical error. ...
I'll be a little more specific. We HAD been assuming the single degenerate hypothesis for a long time (Thanks Chandra!) but it has become fairly clear in the last few years that the double degenerate hypothesis (two white dwarfs spiraling into each other) probably accounts for more than half of the type Ia SN. Jerry's statement was that if it isn't SD, then we simply have no idea what it is, but of course we do have an idea, and Jerry's not mentioning it is a misleading rhetorical form (not so much an error), since he himself has selected dozens of papers for the Fun Papers thread about the Double Degenerate hypothesis.

Schneibster
2014-Feb-17, 12:11 AM
Yes, I'm familiar with that debate, though I haven't been on science forums for a few years so although I pretty much read Science Daily four times a week I still miss a lot. So thanks for the context!

I had heard, though I cannot currently recall where or what, that there was more evidence than just this against the single-dwarf-hits-Chandra's-Limit scenario. Is there a summary thread for it?

I saw someone mention SN1987a and thought of bringing up that it was a Type II, and a peculiar at that, so not very useful for studying Type Ias.

antoniseb
2014-Feb-17, 12:28 AM
... Is there a summary thread for it? ...
I don't recall a summary thread. The main evidence is basically the same as we see here, Most Ia SN that we can test don't show either a companion star, or evidence for a planetary nebula or other debris from the pre-SN part of the process. Hence they are double degenerate. This also helps explain why some of the Ia SNs are over bright.

Schneibster
2014-Feb-17, 12:32 AM
We're talking about asymmetries in the explosion caused by the obstruction of the non-degenerate, presumably modified main-sequence star, right? (Modified by the mass loss, I mean.)

Would we expect it to be blown apart, or for there to be a remnant?

Schneibster
2014-Feb-17, 12:49 AM
And on SN1987a, its importance was that it sequentially lit up shells of dust and gas it had previously shed, so that the speed of light could be measured remotely by the angular size of the rings of shells of gas and dust. This speed of light could then be compared to the speed of light in the laboratory, and they were found to be the same, providing good evidence against theories of physics that propose a changing speed of light that varies according to time or distance.

Not that I exactly expect to find any YECs on Bad Astronomy. Snicker.

Don Alexander
2014-Feb-17, 08:42 AM
There would definitely be a remnant. Especially considering in the single-degenerate case, it is reasonably likely that the donor star has become rather compact due to losing its outer shell due to mass loss.

I'd additionally like to point out that iirc the upper limit on a donor star was something like absolute magnitude -7 or so? That rules out a supergiant donor but not more compact configurations with less massive stars.

I'm a bit out of my depth here, though.

Schneibster
2014-Feb-17, 08:49 AM
Bwahaha, I'm swimming in shark-infested waters, don't worry about depth. :D

Meanwhile, what's a -7 on the main sequence, isn't that a hot A or even a blue-white B?

ETA: OK, hang on I'm looking it up, update to this post coming up momentarily...

Wow! Yeah, I was right, Sol is like +5, big hot As are like 0, and -5s are blue-white supergiant Os and [B]s. [Note: apparently I hit a warning for a common abbreviation for an epithet, when I attempted to pluralize B. Amusing.] A -7 is like maybe a Wolf-Rayet star or something even gnarlier, way up at the top left. Check it out: http://en.wikipedia.org/wiki/File:HRDiagram.png

Did you perhaps mean absolute magnitude 7? That would be a star that at 10 parsecs distance, that is at 32.6 light years, would be just below the limit of human visibility after extensive dark adaptation on the finest night of the year on the nearest 1000 meter hill or mountain you can conveniently access, far beyond any city light dome. If your eyes were absolutely incredible you might just barely see a glimmer. You could easily see it with cheap binoculars under those conditions.

A lot of people get it mixed up. The minus numbers are the brightest stars. Zeros are "bright stars" (whatever the heck that means, more or less; you'll find lists of "the first magnitude stars" more or less list about fifty of them). There are a few minus stars, a handful of zero stars, and a score or two of ones, in our sky. Do some mumbo-jumbo and finagle up with some numbers and define "magnitudes" well enough to have two places of precision, then classify stars by normalizing their distance to 10 parsecs defining their brightness in your cargo cult "magnitudes." :D

I'm just teasing. I know how magnitudes are defined.

Jerry
2014-Feb-17, 09:36 PM
Jerry, you've made a logical error.

You're assuming that because this event didn't have the single-dwarf hypothesis as a progenitor, no event has it as a progenitor. That's a non sequitur; literally, "it does not follow."
No it is not a logical fallacy. If you had a theory that butterflies grew out of 'tree buds' and not caterpillars, you only need one example of a butterfly emerging from a chrysalis to null the 'tree bud' theory and start looking for caterpillars. We don't know what the progenitor is, but at the very least it has to be acknowledged that the single degenerate precursor may not exist. Also, the relative uniform spectral signatures and narrow magnitude ranges of these supernova events beg for a single type of progenitor; not two.

The double-degenerate model is still plausible; but I think that it is on shaky ground; since even in the double generate scenario, at least one of the precursors should be a white dwarf of sufficient mass, temperature and size to be visible in these Hubble high resolution studies of M82 before this event.



OTOH, I agree they should look for another precursor or progenitor. And I would guess that statement in their paper was intended to say exactly that. .

Of all the things that have refused to show up where we expected to find them; to me, this one is the most surprising.

antoniseb
2014-Feb-17, 10:05 PM
... in the double generate scenario, at least one of the precursors should be a white dwarf of sufficient mass, temperature and size to be visible in these Hubble high resolution studies of M82 before this event.

No, don't think so. White Dwarfs have absolute magnitudes of 10 or more typically, getting dimmer as they age. At the distance to M82, this means it would have an apparent magnitude of +37 which is well beyond Hubble's grasp.

StupendousMan
2014-Feb-18, 12:02 AM
The double-degenerate model is still plausible; but I think that it is on shaky ground; since even in the double generate scenario, at least one of the precursors should be a white dwarf of sufficient mass, temperature and size to be visible in these Hubble high resolution studies of M82 before this event.


Let me echo Antonsieb here: this statement is not only wrong, it's VERY wrong. The images taken by HST before the supernova occurred have a limiting magnitudes in the near-IR of around m = 21 mag (Goobar et al., http://arxiv.org/pdf/1402.0849v2.pdf). This may sound rather bright for the limiting magnitude of HST imagery, and it is, but for two reasons. First, the field is crowded, so if one takes longer exposures, one starts to see a nearly continuous sheet of light, making it difficult to distinguish individual objects; and second, because there aren't really long exposures of M82 at these near-infrared wavelengths. This portion of M82 is rich in dust, so trying to work in the optical passbands doesn't work very well.

Okay, so, the limiting magnitude in J-ish bands is around m = +21. The distance modulus to M82 is about (m - M) = 27.7 (see NED), so that means that limit on the absolute magnitude in J-band would be roughly M = m - 27.7 = 21 - 27.7 = -7, as a round number.

Now, in the single-degenerate scenario for Type Ia SNe, a white dwarf in a close binary system with a non-degenerate companion accretes material from the companion. The accretion produces both optical and X-ray emission, causing the system to be significantly more luminous than an isolated white dwarf or an isolated non-degenerate star. Exactly how luminous is a good question: it depends on the nature of the accretion and the rate at which material is transferred. So it would be tough to put a strong limit on the absolute magnitude of a single-degenerate system with any certainty.

But Jerry's statement mentions the double degenerate scenario, in which two white dwarfs orbit each other. In this case, there is no accretion until the two stars come so close that one (or both) are ripped apart by tidal forces. Therefore, each white dwarf just shines like, well, a single, isolated white dwarf. Do we know how luminous an isolated white dwarf is in the J-band? Well, it depends on the age of the white dwarf as well as on the mass, so there's no single answer. But values might range from M = +8 to +13, with many more objects at the faint end because they spend much more time there.

So, the observational limit in this case is around M = -7, and the typical absolute magnitude of an isolated white dwarf is around M = +10. In other words, the actual brightness of a white dwarf in M82 would be 17 magnitudes fainter than the limit. To make the claim that



The double-degenerate model is still plausible; but I think that it is on shaky ground


on this basis is more than wrong.

I make mistakes often -- I've done so in postings to this bulletin board, and I've done so in class in front of my students. I've even made mistakes in papers I've submitted to journals, though fortunately, my co-authors and referees have caught most of them. But when one makes the claim that a generation of scientists should be ready to give up their models and start afresh, one really ought to double-check one's calculations.

Don Alexander
2014-Feb-18, 11:39 AM
Did you perhaps mean absolute magnitude 7?
Schneibster, I have a PhD in astrophysics. I meant -7. ;)

And please remember that you don't need a main-sequence star. Evolved cool stars (red giants and supergiants) are much better as donor systems as they fill out their Roche limits much more easily.

Jerry
2014-Feb-19, 08:00 AM
I make mistakes often -- I've done so in postings to this bulletin board, and I've done so in class in front of my students. I've even made mistakes in papers I've submitted to journals, though fortunately, my co-authors and referees have caught most of them. But when one makes the claim that a generation of scientists should be ready to give up their models and start afresh, one really ought to double-check one's calculations.
The double degenerate (DD) model was not developed to provide an answer when a white dwarf it is not detected as a source of a typical supernova Ia event. The DD model arose because of certain spectral features (such as polarity), and possible asymmetry in some supernova after shocks. (Although these can often be accounted for as environmental factors.)

The primary reason for the DD model is that a small percentage of supernova events that are either super-luminous and subluminous while still displaying fairly textbook light curves. The DD scenario still requires a Chandrasahkar or greater mass, and is generally thought to be a less efficient generator of a supernova event: It is really, really difficult to model an asymmetric explosion with anywhere near optimal yields. In any likely DD scenario, at least one, if not both of the stars should be very close to the 1.4 textbook mass if this is the mechanism behind supernova Ia events.

I concede (as I stated) the reddening of the the environment masks the event so that a DD source cannot be ruled out; but again, this is a 'standard' type Ia; so if the single degenerate model is viable; this should have a single source. (If the light-curve were exceptionally long or short; it is easy to say this is an unusual and therefore likely a DD event.)

Once again, there is absolutely no proof that the 'critical white dwarf' is the correct model for supernova events. There is plenty of evidence the range of magnitudes is curiously tight in most events; but with broad exceptions. We should expect the predicted beast to be found in the right place before the explosion. It is not.

Amber Robot
2014-Feb-19, 06:06 PM
The DD model arose because of certain spectral features (such as polarity)...

Do you mean "polarization" here?

Ken G
2014-Feb-20, 01:48 AM
(If the light-curve were exceptionally long or short; it is easy to say this is an unusual and therefore likely a DD event.)I don't understand why you conclude a DD event should have a different light curve. What is the justification for that belief? If most Ia are DD, then one should expect a normal light curve if it is DD. Also, why would you expect both stars to be near 1.4 as a requirement for a DD? Certainly, one should not expect most Ia to be from two stars that are both near 1.4, that takes 2.8 to begin with.


Once again, there is absolutely no proof that the 'critical white dwarf' is the correct model for supernova events. Astronomy and "proof" rarely come together, but if you have any remotely plausible alternatives for Ia than critical WDs, I'd like to hear about it.
There is plenty of evidence the range of magnitudes is curiously tight in most events; but with broad exceptions. We should expect the predicted beast to be found in the right place before the explosion. It is not.I thought it was pretty clearly pointed out that no one in their right mind should expect a Ia to have a visible progenitor unless it has a bright mass-losing companion or is strangely young.

Jerry
2014-Feb-20, 05:23 AM
I don't understand why you conclude a DD event should have a different light curve. What is the justification for that belief? If most Ia are DD, then one should expect a normal light curve if it is DD. True. It is possible that the 'double hump' in the light curve is evidence of a double-d event. We don't always see the double peak; be we don't always have enough observations to observe it. So it is possible all events are dd's.

But in making this assessment, you are really throwing out the reasoning behind the White dwarf model: A mass-driven event that explains the high level of uniformity in the magnitude of these events. Moving to primarily DD events throws-out the reasoning behind a critical mass-driven event. It takes away the reasoning behind why white dwarfs are thought to be the precursors of supernova type Ia.



Also, why would you expect both stars to be near 1.4 as a requirement for a DD? Certainly, one should not expect most Ia to be from two stars that are both near 1.4, that takes 2.8 to begin with. Yes you should - at least one of them. You would not expect, say, two 0.8 Mass white dwarfs to collide in such a way that the nuclear conversion process would be complete - this would be a very dirty and inefficient bomb.


Astronomy and "proof" rarely come together, but if you have any remotely plausible alternatives for Ia than critical WDs, I'd like to hear about it.I thought it was pretty clearly pointed out that no one in their right mind should expect a Ia to have a visible progenitor unless it has a bright mass-losing companion or is strangely young.
To be honest; without the Chandrasahkar model, I am at a complete loss to explain how an event of this magnitude is possible. But as I have said many times; we don't have to have a working model. We do need to throw-out ideas that have out-lived their usefulness, such as inflation.

And I am confused: It is the authors who ruled-out textbook progenitors, not me:

"Our results firmly rule out the progenitor being a single-degenerate system with a photospheric radius comparable to the near-Chandrasekhar mass white dwarf radius and mass accretion rate in the range where stable nuclear burning can occur."

Jerry
2014-Feb-20, 05:26 AM
Do you mean "polarization" here?Yes - polarity of the spectral signature.

Jerry
2014-Feb-20, 03:57 PM
I make mistakes often -- I've done so in postings to this bulletin board, and I've done so in class in front of my students. I've even made mistakes in papers I've submitted to journals, though fortunately, my co-authors and referees have caught most of them. But when one makes the claim that a generation of scientists should be ready to give up their models and start afresh, one really ought to double-check one's calculations.
Again, it is not the potential magnitude of the parent stars in a DD scenario that makes the model questionable; it is the broad range of possible outcomes from events spawned from two epicenters. If this is what we are witnessing, (and it may be) a much broader range of potential outcomes should be anticipated than the current magnitude limits assigned to a high majority of the supernovae we have observed.

And that is the irony: In moving to a DD scenario; a generation of scientist do need to go back and make realistic estimates of the range of magnitudes a white dwarf family of supernova events should encompass; starting with the assumption that the most distant events we are likely to observed are dominated by over-magnitude events.

Ken G
2014-Feb-20, 06:18 PM
But in making this assessment, you are really throwing out the reasoning behind the White dwarf model: A mass-driven event that explains the high level of uniformity in the magnitude of these events. Moving to primarily DD events throws-out the reasoning behind a critical mass-driven event. It takes away the reasoning behind why white dwarfs are thought to be the precursors of supernova type Ia. I don't model DDs, so I can't speak with authority, but I assure you that those who do are not idiots. They are aware that if you merge two 0.8 M WDs, you have 1.6 M there, and so they have a puzzle as to why they are trying to explain a 1.4 M explosion. If your argument had merit, their models would have been discarded. I think we should be concluding that the models are able to explode a 1.4 M star starting with two 0.8 M stars! I presume the idea is that a central 1.4 M portion implodes as more and more gas goes relativistic, leaving the rest behind as flotsam in the ensuing eruption. The details of how that happens, I cannot say.


To be honest; without the Chandrasahkar model, I am at a complete loss to explain how an event of this magnitude is possible.Neither can anyone else, that's how you can be sure the DD scenario also invokes the Chandrasekhar model.


"Our results firmly rule out the progenitor being a single-degenerate system with a photospheric radius comparable to the near-Chandrasekhar mass white dwarf radius and mass accretion rate in the range where stable nuclear burning can occur."That's what I meant by "unless it has a bright mass-losing companion." But you do have a point that if it doesn't have a bright mass-losing companion, it's hard to see how the single-critical-WD model could work, so that can be taken as a plus for the DD model camp. You just seem more worried about the homogeneity of the sample of type Ias than they are-- you expect the DD scenario to show more variations and make a lousy standard candle, but the DD modelers must not share that view or they would not be suggesting that mechanism. Still, I must admit that if your main point is taken to be "there is still much about type Ias that we have yet to figure out", I cannot dispute that.

Jerry
2014-Feb-20, 08:55 PM
Ok, here is a paper on the luminosity of DD scenarios that is very supportive of Stupendousman's assertion that DD sources would be undetectable:

http://arxiv.org/pdf/1310.2170.pdf A population synthesis analysis using SeBa


Conclusion: The population of double-degenerate type Ia supernova progenitors that are supersoft X-ray sources is at least an order
of magnitude smaller than the population of single-degenerate progenitors expected to be supersoft X-ray sources, and the supersoft
X-ray behaviour of double-degenerate systems typically ceases long before the supernova explosions.

Also:

The conclusions we make from this is that we do not expect a significant number of proto-DD type Ia SN progenitor to be observable as SSSs as a result of pure wind mass transfer. This goes contrary to what was concluded in the study by Di Stefano, which predicted thousands of these sources.

This is significant, because the 'wind induction' model of Stefano would be highly luminous for a long period of time.

Next time there is a nearby event, would someone please make sure that the dust is settled before pushing the button, because we can't tell exactly what is happening.

jimmarsen
2014-Mar-05, 04:41 PM
Here's an article about a paper that may contribute to the type Ia SN debate: Standard-candle supernovae are still standard, but why? (http://www.sciencedaily.com/releases/2014/03/140304094841.htm)

It refers to this Arxiv preprint: Type Ia supernova bolometric light curves and ejected mass estimates from the Nearby Supernova Factory (http://arxiv.org/abs/1402.6842)

Jerry
2014-Mar-15, 07:03 PM
http://arxiv.org/pdf/1401.7968v2.pdf Estimating the First-Light Time of the Type Ia Supernova 2014J in M82 Notes the significant dust reddening we have talked about above. However, Foley, Mandel and Kirskner have been looking at a relationship between expansion velocity and apparent reddening and concluded that high velocity events, like 2014J, contain line dampening that skews the reddening calculations; so it may not be as dusty as it looked at first blush:

http://arxiv.org/abs/1402.7079 Type Ia Supernova Colors and Ejecta Velocities: Hierarchical Bayesian Regression with Non-Gaussian Distributions