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Fraser
2005-Apr-28, 05:35 PM
SUMMARY: Astronomers have theorized that Mira AB is a binary star system consisting of an evolved red giant star and a white dwarf star, and now the Chandra X-Ray Observatory has been able to resolve their relationship. Chandra can actually resolve the stream of matter flowing off the red giant, which is then captured by the white dwarf. This matter heats up as it bunches up around the white dwarf, and blazes in the X-ray spectrum. Mira AB is only 450 light-years away, and the stars are separated by approximately twice the distance of the Sun and Pluto.

View full article (http://www.universetoday.com/am/publish/chandra_interacting_stars.html)

What do you think about this story? Post your comments below.

om@umr.edu
2005-Apr-28, 05:42 PM
It is great when observations fit theory so well!

It is intriguing that material is streaming from "a highly evolved giant star" onto a "collapsed star such as a white dwarf, black hole or a neutron star."

Is it possible that the white dwarf actually has a neutron star at its core?

Thanks, Fraser.

Oliver
http://www.umr.edu~om (http://www.umr.edu/~om)

antoniseb
2005-Apr-28, 05:46 PM
I wonder if that IS a bridge, or if it is an artifact of the overlapping of two extended unresolved blobs. I look forward to seeing higher resolution images of this in another ten years or so when the high resolution xray probe gets operating.

It will be very interesting to work out the science that could result in this bridge if it really exists. The distance of 6.5 billion miles is a long way for electro-magnetic forces to operate for stellar mass objects.

lswinford
2005-Apr-28, 07:40 PM
Antoniseb's estimation was what I first thought of too.

I wonder what the estimated relative ages are for these two stars. Suppose that an older, more massive star (B) captured a wanderer (A). In its capture it (B) began to draw material from the new companion (A), and like a siphon the mechanical flow has begun and not to soon end until the equilibrium changes at some future point.

What is the thinking these days, that binaries are predominantly captured or environmentally formed together (fraternal or identical twins--of which one ate better than the other)?

lswinford
2005-Apr-28, 07:58 PM
Eek! I forgot that characters too close to the parenthesis will sometimes represent other things, at least smiley faces in this case, whew.

John L
2005-Apr-28, 08:26 PM
It is intriguing that material is streaming from "a highly evolved giant star" onto a "collapsed star such as a white dwarf, black hole or a neutron star."There is only a mention of a white dwarf. I see no mention of the possibility of a more dense compact object such as a black hole or neutron star.


Is it possible that the white dwarf actually has a neutron star at its core?No. It isn't.

I agree with Anton that we shouldn't jump to conclusions with such a fuzzy image. There are many possible explanations of the x-ray emitting material between the two stars that future observations at higher resolutions should clarify.

antoniseb
2005-Apr-28, 09:31 PM
Originally posted by John L@Apr 28 2005, 08:26 PM
There are many possible explanations of the x-ray emitting material between the two stars that future observations at higher resolutions should clarify.
One possibility is that these stars have a highly elliptical orbit, and that their is a streamer, but it is the result of the last close pass. I suspect that Mira (Omicron Ceti) is well enough studied that this can't be the case, but after a quick look I still haven't seen the orbital parameters for this pair. Further, there are some big discrencies including one web-site that says Mira A is 15.7 solar masses, and Mira B is about 4 solar masses, and yet Mira B is also called a white dwarf, which can't be 4 solar masses, unless half that mass is in the accretion disk.

John L
2005-Apr-28, 09:50 PM
Was the source Hiparcos, because they're always wrong...

om@umr.edu
2005-Apr-28, 10:14 PM
Originally posted by John L@Apr 28 2005, 08:26 PM

It is intriguing that material is streaming from "a highly evolved giant star" onto a "collapsed star such as a white dwarf, black hole or a neutron star."There is only a mention of a white dwarf. I see no mention of the possibility of a more dense compact object such as a black hole or neutron star.


Is it possible that the white dwarf actually has a neutron star at its core?No. It isn't.

Hi, John L.

Did I misunderstand the 1st and 3rd paragraphs of the full article, shown below with a portion underlined by me ?

Paragraph 1: For the first time an X-ray image of a pair of interacting stars has been made by NASA's Chandra X-ray Observatory. The ability to distinguish between the interacting stars - one a highly evolved giant star and the other likely a white dwarf - allowed a team of scientists to observe an X-ray outburst from the giant star and find evidence that a bridge of hot matter is streaming between the two stars.

Paragraph 3: X-ray studies of this system, called Mira AB, may also provide better understanding of interactions between other binary systems consisting of a "normal" star and a collapsed star such as a white dwarf, black hole or a neutron star, where the stellar objects and gas flow cannot be distinguished in an image.

Are you certain that "normal" nuclear material never streams from "a highly evolved giant star" onto a "collapsed star such as a white dwarf, black hole or a neutron star" ?

With kind regards,

Oliver
http://www.umr.edu/~om

Greg
2005-Apr-28, 10:31 PM
My first impression when I saw the photo of this system was alarm. If this is a white dwarf-red giant system then the end result could be a Type Ia supernova. A ticking time bomb so to speak. Here's hoping this system is red shifted with regards to our system. The fact that the second object is 4 solar masses argues that the matter stream could be an artifact of poor resolution and their proximity to each other. If the matter stream is real and the thing is 4 solar masses, then the white dwarf probably doesn't have very far to go (doesn't have to accrete very much more matter) before it blows. What is the safe distance radius from a type Ia supernova, anyway? Does anyone have an idea how much matter a white dwarf needs to accumulate before it explodes?

Greg
2005-Apr-28, 10:45 PM
Ok I did some research and answered on of my questions, which of course generates another. The supposed mass limit of a white dwarf before it explodes is 1.4 solar masses. So if this object is 4 solar masses then how can it be a white dwarf? It should have exploded long before it reached this size.

wstevenbrown
2005-Apr-29, 02:20 AM
The full listing of the source document is : X-Ray Outburst in Mira A
Author: M. Karovska et al., ApJL Vol 623 pp137-140

It is available by subscription only. Here is the abstract. Anybody got a subscription? :( Steve


A Large X-Ray Outburst in Mira A1
Margarita Karovska ,2 Eric Schlegel ,2 Warren Hack ,3 John C. Raymond ,2 and Brian E. Wood 4
Received 2004 December 24; accepted 2005 March 8; published 2005 March 25
ABSTRACT
We report the Chandra ACIS-S detection of a bright soft X-ray transient in the Mira AB interacting symbiotic-like binary. We have resolved the system for the first time in X-rays. Using Chandra and Hubble Space Telescope images, we determine that the unprecedented outburst is likely associated with the cool asymptotic giant branch (AGB) star, Mira A, the prototype of the Mira class of variables. X-rays have never before been detected from an AGB star, and the recent activity signals that the system is undergoing dramatic changes. The total X-ray luminosity of the system is several times higher than the luminosity estimated using previous XMM-Newton and ROSAT observations. The outburst may be caused by a giant flare in Mira A associated with a mass ejection or a jet and may have long-term consequences on the system.
Subject headings: binaries: symbioticstars: activitystars: AGB and post-AGBstars: individual (Mira AB)stars: winds, outflowsX-rays: general

1 We dedicate this paper to the memory of Janet A. Mattei, who inspired this work and made these observations possible for many years.
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218.
4 JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440.

Greg
2005-Apr-29, 06:18 AM
Ok, After further deliberation, my best guess is that this is a binary system with a white dwarf-red giant pair. The dwarf is surrounded by an accretion disc containing at at least 3 solar masses of material in it.
Does this mean it is certain that the dwarf will accrete enough of the material in the disc to explode? I don't think anyone knows the answer for sure, but it seems likely that it would do so in time. At least one can say that it is possible.
The good news is that most dense objects are sloppy eaters and consume only a fraction of what is in its disc ejecting the rest as high energy particles along its polar axis (ie the x-rays detected by Chandra which usually come from the B component of the system.)
I can only imagine that if the dwarf doesn't already have enough material to eat, what would happen when the A component ejects more and more mass and forms a planetary nebula? My guess is that the outflows would disrupt the disc and add lot of material quickly to the star (like one giant gulp of matter as opposed to picking a bit here and there.) Such an event resulting from an outflow might be enough to cause the dwarf to blow as a Ia supernova with those mysterious hydrogen emission lines (outflow matter caught up in the blast) that are seen associated with one from time to time.

Nereid
2005-Apr-29, 06:18 AM
Here (http://arxiv.org/abs/astro-ph/0503050) is the preprint.

antoniseb
2005-Apr-29, 03:17 PM
Originally posted by Greg@Apr 28 2005, 10:45 PM
The supposed mass limit of a white dwarf before it explodes is 1.4 solar masses. So if this object is 4 solar masses then how can it be a white dwarf? It should have exploded long before it reached this size.
There are some things about the data concerning this system that don't make sense. Strangely, the 425 year orbit should be pretty well understood now. We've had the capability to resolve this pair visually since Hubble got its vision corrected.

The star is an important one in our understanding of the universe, and is well studied. It is bright and nearby. WHY can't I find reliable data about it's orbital elements and some solid study showing what the masses of these objects really are?

om@umr.edu
2005-Apr-29, 05:49 PM
Originally posted by antoniseb+Apr 29 2005, 03:17 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb &#064; Apr 29 2005, 03:17 PM)</td></tr><tr><td id='QUOTE'><!--QuoteBegin-Greg@Apr 28 2005, 10:45 PM
The supposed mass limit of a white dwarf before it explodes is 1.4 solar masses. So if this object is 4 solar masses then how can it be a white dwarf? It should have exploded long before it reached this size.
WHY can&#39;t I find reliable data about it&#39;s orbital elements and some solid study showing what the masses of these objects really are?[/b][/quote]
Hi, Anton.

If you find the answers, I hope you will post them here.

Thanks,

Oliver
http://www.umr.edu/~om

Erimus
2005-Apr-29, 06:07 PM
I&#39;ve been interested in the Mira system for some time, so I&#39;ve looked hard for information on the system myself.

Hipparcos gives a distance estimate 128 pc for Mira, with an margin of error of 14 percent, which isn&#39;t bad. A more recent estimate from a 2004 abstract gives an estimate of 107 pc for the system, with a slightly better error margin of about 11 percent. All this information can be found with a SIMBAD query.

Unfortunately, the orbital elements of the system are poorly known, so the masses are quite uncertain as well. Robert Burnham Jr. states in his famous (but dated) tome that the best estimate for the total mass of the system is 3.7 solar masses, though he doesn&#39;t indicate his source.

Here are the orbital elements I was able to dig up on the system on the Sixth Orbit Catalog; I&#39;ve omitted data that was irrelevant to the orbit, such as misc. nomenclature and celestial coordinates:

[Edit: Mira, by the way, is also ADS 1778, for ease of looking up...]

V_1
3.0 v
V_2
9.6 v
Period
497.88 y
Semimajor axis
0.800 arcseconds
Inclination
112.0
Long. of Ascending Node (omega)
138.8
T (Periastron)
2285.75 y
eccentricity
0.160
Long. of Periastron (w)
258.3

link:
http://ad.usno.navy.mil/wds/orb6/orb6frames.html

It should be noted that the orbit grade code for this system indicates that its orbit is very poorly known, as stated before.

wstevenbrown
2005-Apr-29, 06:42 PM
So we are seeing it just prior to apastron, not that it makes much difference with such a low eccentricity.

I am curious what sort of interaction between the components Ms. Karovska had in mind, given the 70 AU separation.

BTW, thanks All, for adding such data as are available. I&#39;d&#39;a found the arxiv link myself if I hadn&#39;t been so tired and PO&#39;d with the ApJL website.

When I was first acquainted with Mira, it was described as a pulsating semiregular variable. There was no clue about a companion of any sort, accretion disk, interaction, etc. So today&#39;s data are incomplete? Still, better than before&#33;

So what has a companion with a period of 181,851 days got to do with Mira&#39;s 331 day (avg) period? Probably nothing. I would be very surprised if those fuzzy spectral lines didn&#39;t turn out to be C and N. I think the description of the companion may be in error. It&#39;s possible to be a dwarf of spectral class A without being a white dwarf-- given the separation, no danger of supernova this week.

Best regards-- Steve

Duane
2005-Apr-29, 07:26 PM
Did I misunderstand the 1st and 3rd paragraphs of the full article, shown below with a portion underlined by me ?

Seems like you&#39;ve misunderstood it. The 1st paragraph states that the companion around this star is a white dwarf, whereas the 3rd papragraph states that understanding this system will give scientists an understanding of similar systems where a small, compact object orbits a large companion.

There is no neutron remnant in a white dwarf. Don&#39;t start this crap again. :angry:

A white dwarf will explode at 1.4 solar masses, as at that point it passes the Chandra Limit. This dwarf seems to be doomed, and I wonder how its closeness may affect our solar system, when it finally goes off.

Anton, I think the problem with the mass calculations is due to the gas around the pair. Up till now, I don&#39;t think there were pictures with the resolution needed to determine the actual mass of the pair. In other words, the mass given for the system was a "best guess" with the info available at the time.

lswinford
2005-Apr-29, 07:48 PM
wstevenbrown, what if the cycle represents some clumpiness to the siphoning. Sort of a periodic gurgling, like with a geyser. Material is in motion, drawn down the stream to the companion, but then relatively pauses while masses resettle themselves. Perhaps there is a sort of wave action, where a mass or bubble from down lower in the star rises to ejection, followed by other masses settling in place, precipitates other motions, which give rise to the next bubble to rise for ejection. :rolleyes:

Even so, if there was a comparative mechanical process behind the variability, does the observational record correlate with any pattern that jives with the apparent conjunction and separation as they orbit? I too would have thought that such a longer-term cycle of waxing and waning would have been noted somewhere, unless they were guessing a Mira equivalent of sunspot maximum/minimum cycles like our sun does. :unsure:

wstevenbrown
2005-Apr-29, 09:02 PM
I&#39;m still having trouble with the siphoning. Mira&#39;s extended envelope has a radius of ca. 5AU, and most of it is so very thin as to be almost vacuum. What could make hot gas march in lockstep the additional 65AU? I rather suspect the crystallized Carbon dust is being preferentially hauled in by the dwarf, since it is much cooler. Hmm... then the accretion events would stand in a phase relationship with the Carbon-ejection events, the basis for Mira&#39;s variability...

More coffee&#33; ;) Steve

Greg
2005-Apr-30, 04:42 PM
I like the idea of there being a direc tonnection between the accretion process and the mass ejection events. My guess is that when this dwarf blows it will contain a hydrogen emission line. The reason for this would be that it is most likely to add mass during an ejectection event when there would be lots of hydrogen in its vacinity.

lswinford
2005-May-02, 06:41 PM
BTW: with the various guestimates of the mass sizes, where would the center of gravity for this binary be?

wstevenbrown
2005-May-02, 09:32 PM
I&#39;ve been going over recent pubs on the Mira AB system. There is no consensus on the precise nature of the accreting body. I should hasten to add that it is definitely wind accretion, not the more serious Roche Lobe version. There is contradiction in the literature as to whether or not the accreting body is even experiencing mass gain at all. Its own wind may exceed the infall from the accretion disk. So no need for supernova evac procedures. It is flatly impossible to obtain a spectrum of the central body, which is swamped by the emission and fluorescence spectrum of the disc. The identifiable lines are those of CIII and H2-- pretty much as expected. The central mass is somewhere between .5 and .7 MSol, so it can be anything between an M dwarf and an A dwarf, or it can be a true white dwarf. The general character of the disk and its excitation favor the latter.

Contrary to my earlier speculation, there is no link between Mira A&#39;s carbon-puffing period of 331d and the accreting body&#39;s photoperiod. The shocked Carbon simply piles up against the disk edge. In the CIII lines, there has been tentatively identified a 14-yr photoperiod, which is possibly due to the precession of the disk. Any variability of the central object is lost in the glare of the disk.

To form your own opinions, see:

http://arxiv.org/astro-ph/0503050 (Karovska et. al)

http://arxiv.org/astro-ph/0310105 (Wood and Karovska)

http://arxiv.org/astro-ph/0408329 (Kastner and Soker)

http://arxiv.org/astro-ph/0404248 (Woodruff et. al.)

To be so close and yet so unknown-- truly this belongs over in my Weird Neighbors string&#33; :rolleyes: Steve

drjgokhale
2005-Jun-01, 04:05 AM
Originally posted by Greg@Apr 28 2005, 10:31 PM
My first impression when I saw the photo of this system was alarm. If this is a white dwarf-red giant system then the end result could be a Type Ia supernova. A ticking time bomb so to speak.
Aren&#39;t we living in a universe full of those anyway? What are stars if not not a a million nuclear bombs each roughly speaking? Not to mention the planet we live on is quite alive with volcanoes (think Yellowstone) and shifting continental plates (earthquakes, volcanoes, tsunami) and iceland being pulled apart in the middle by the american plate going away from the european. And so on and so forth.

It is wonderful to have life exist in the midst of all this and be conscious enough to support thought enough to observe it all and discuss it. Isn&#39;t it?

Fascinating, the system of these two stars. Would be good to keep in touch with what else is known about them hereon.