What is this object?

[wonderboy]

I still do not know what the hell it is thats moved. could someone quite crudely repost the picture with a circle round it? please.

[geckzilla]

[BDanielMayfield]

If I buy a book on astrometry and put it under my pillow I'll know how to do this in the morning, right?

I think you have to open it to the correct page before putting it under your pillow. Meme transfer can't get through the hardcovers, so you need to reduce the barriers to be able to absorb knowledge this way. Or buy a softcover book, I guess.

Rob

(I wrote the following prior to seeing Rob's reply.)

Hmm … I would say that success is highly unlikely geckzilla, unless …

I. Leave light on in sleeping area.
II. Open text to relevant page(s).
III. Use transparent pillow.
IV. Sleep face down with eyes open.

As the above outline is bound to be uncomfortable and very unrestful, it is not recommended.

[BDanielMayfield]

Well I’d hate to have my last comment (meant in jest, of course) be the last word on this interesting thread. I think that Geckzilla may have actually found a very interesting object here, so her question deserves more consideration, IMO.

It appears to me that there are three main possibilities here. (1) It’s small object inside our solar system. (2) It’s a foreground star unassociated with this nebula. (3) It’s a star that has escaped from the system back when the stellar mass ejection that created the nebula occurred.

The first possibility seems to have already been looked into and eliminated by Geckzilla:

I thought it could be some kind of trans-Neptunian object but when I compared it to those I realized it moves a lot more slowly. So maybe it is just a nearby star and the movement is just parallax.

In any event, I think that the odds for both (1) and (2) are slim due to probability. The chance that either a small solar system body or a nearby star would randomly appear to be flying directly away from a star that has recently erupted would have to be very small. Therefore I think that the suggestion Art raised (3) is on target.

What would make the association even more convincing would be if the ejected lobes and the possible runaway star’s locations backtracked in time were to converge upon the star between the two lobes. I think this should be investigated, and if the object is confirmed to be a star flung from orbit around the star that ejected this planetary nebula then since she pointed it out it should be officially named Geckzilla’s Star.

[Chris Peterson]

In any event, I think that the odds for both (1) and (2) are slim due to probability. The chance that either a small solar system body or a nearby star would randomly appear to be flying directly away from a star that has recently erupted would have to be very small. Therefore I think that the suggestion Art raised (3) is on target.

I think a foreground or background star, unconnected with the nebula, is the most likely. The process that creates planetary nebulas is not particularly violent; I don't really see a mechanism that could eject a component star in the same system (and it clearly isn't the parent star of the nebula). The only examples I know of where we have ejected stars involve supernovas, and even then are rare.

There are other stars in the field which are obviously unrelated to the planetary nebula system. We'd expect that, and there's nothing odd about one of them having a significant, although still fairly small proper motion.

[BDanielMayfield]

In any event, I think that the odds for both (1) and (2) are slim due to probability. The chance that either a small solar system body or a nearby star would randomly appear to be flying directly away from a star that has recently erupted would have to be very small. Therefore I think that the suggestion Art raised (3) is on target.

I think a foreground or background star, unconnected with the nebula, is the most likely. The process that creates planetary nebulas is not particularly violent; I don't really see a mechanism that could eject a component star in the same system (and it clearly isn't the parent star of the nebula). The only examples I know of where we have ejected stars involve supernovas, and even then are rare.

There are other stars in the field which are obviously unrelated to the planetary nebula system. We'd expect that, and there's nothing odd about one of them having a significant, although still fairly small proper motion.

I concede that stellar mass loss events that create planetary nebulas not being all that violent is a very good point Chris, possibly even being a fatal flaw to this runaway star idea. Considering binary systems, how much mass percentage would a primary star have to lose for the less massive star to break loose? Wouldn’t the orbital distance between the pair just increase by an amount proportional to the mass loss instead of the system being disrupted altogether? One thing is certain, no matter what happened here, the laws of physics weren’t violated, and I would never suggest such a thing.

However, I still come back to the observational alignment of things seeming to all be radiating out from the nebula’s central star, both in apparent position and possibly also temporally as well. The alignment seems too perfect for this to be a mere coincidental alignment, IMO. As you say Chris, there’s nothing odd about the rate of this star’s motion, but if backtracking its motion leads back to the central star at the very time of the nebula’s creation, well then that would be odd, wouldn’t it?

Chris, you are most likely right, and geckzilla’s mystery object is just a mundane, unrelated foreground or background star. But if it turns out that they were indeed formerly close could it be possible that we might have cause and effect reversed? Could a rare close encounter between passing stars trigger a planetary nebular outflow to begin? As I reread what I just wrote I can see that I have just suggested something that must be incredibly rare in order to replace an explanation that may be only somewhat rare. But this last idea removes the problem of the planetary nebula’s insufficient force as a cause for the runaway star’s motion.

[neufer]

Geckzilla should at least follow her astrometry ambition up enough to count the pixels so as to estimate about how long ago the moving star would have passed near the brighter star from our perspective.

[geckzilla]

174.52 pixels if you want to do the math with our current numbers, but the age of the nebula itself is still uncertain along with the distance. It's not very exacting astrometry unless you don't mind measuring things with a crazy ruler made of mist and unicorns. There's an Adventure Time episode there somewhere.

[BDanielMayfield]

Geckzilla should at least follow her astrometry ambition up enough to count the pixels so as to estimate about how long ago the moving star would have passed near the brighter star from our perspective.

I agree Art.

174.52 pixels if you want to do the math with our current numbers, but the age of the nebula itself is still uncertain along with the distance. It's not very exacting astrometry unless you don't mind measuring things with a crazy ruler made of mist and unicorns. There's an Adventure Time episode there somewhere.

174.52 pixels is a good start geckzilla. Now it would be nice to know the time span between the two images to better precision too. When were the two images taken?

[geckzilla]

12 years, like I said. The extra 21 days are negligible but you can add them if you want and add on a few leap days while you are at it if you want to measure it by days.
1995-10-24
2007-11-15

[neufer]

12 years, like I said. The extra 21 days are negligible but you can add them if you want and add on a few leap days while you are at it if you want to measure it by days.
1995-10-24
2007-11-15

So roughly 700 years since it was near the central star.

Could it be a very small pink dot, marking a relatively dense and small knot of gas
representing the ejection of gas from the star along a specific direction

[b][color=#0000FF]NGC 2371: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)[/color][/b]

---

<<Probing a glowing bubble of gas and dust encircling a dying star, the NASA/ESA Hubble Space Telescope reveals a wealth of previously unseen structures. The object, called NGC 2371, is a planetary nebula, the glowing remains of a Sun-like star. The remnant star visible at the centre of NGC 2371 is the super-hot core of the former red giant, now stripped of its outer layers. Its surface temperature is a scorching 240,000 degrees Fahrenheit. NGC 2371 lies about 4,300 light-years away in the constellation Gemini.

The Hubble image reveals several remarkable features, most notably the prominent pink clouds lying on opposite sides of the central star. This colour indicates that they are relatively cool and dense, compared to the rest of the gas in the nebula.

Also striking are the numerous, very small pink dots, marking relatively dense and small knots of gas, which also lie on diametrically opposite sides of the star. These features appear to represent the ejection of gas from the star along a specific direction. The jet's direction has changed with time over the past few thousand years. The reason for this behavior is not well understood, but might be related to the possible presence of a second star orbiting the visible central star.

A planetary nebula is an expanding cloud of gas ejected from a star that is nearing the end of its life. The nebula glows because of ultraviolet radiation from the hot remnant star at its centre. In only a few thousand years the nebula will dissipate into space. The central star will then gradually cool down, eventually becoming a white dwarf, the final stage of evolution for nearly all stars.

The Hubble picture of NGC 2371 is a false-color image, prepared from exposures taken through filters that detect light from sulfur and nitrogen (red), hydrogen (green), and oxygen (blue). These images were taken with Hubble's Wide Field Planetary Camera 2 in November 2007, as part of the Hubble Heritage program.>>

[geckzilla]

Those small pink dots don't show up very well in the 555w filter since they are emitting different light. Also, none of them are moving that fast. It's not one of the knots. Not a knot.

[Chris Peterson]

Could it be a very small pink dot, marking a relatively dense and small knot of gas
representing the ejection of gas from the star along a specific direction :?:

The object has the same FWHM as other stars (in both images), so it is almost certainly a stellar source.

[BMAONE23]

I like the image Art posted. The pink area on the left foot side looks like a Left Footprint

And this image

from the WIKI Article makes the entire nebula resemble a Cosmic Candy in a Cellophane wrapper

[geckzilla]

Depending on what data is used it's easier to discriminate between stars and other stuff. I also try to be very careful not to oversharpen point sources like stars so that they don't turn into pure white oversized dots. Anyway, don't want to toot my own horn but look for yourself. It's much easier to see that all the stars are distinct from the nebular knots with my image.

Flickr applies its own sharpening so make sure you right click the image and select original if you want to be even more sure.
http://www.flickr.com/photos/geckzilla/10278558143/

[Chris Peterson]

Depending on what data is used it's easier to discriminate between stars and other stuff. I also try to be very careful not to oversharpen point sources like stars so that they don't turn into pure white oversized dots. Anyway, don't want to toot my own horn but look for yourself. It's much easier to see that all the stars are distinct from the nebular knots with my image.

Flickr applies its own sharpening so make sure you right click the image and select original if you want to be even more sure.
http://www.flickr.com/photos/geckzilla/10278558143/

Like your technical details :)

[BDanielMayfield]

12 years, like I said. The extra 21 days are negligible but you can add them if you want and add on a few leap days while you are at it if you want to measure it by days.
1995-10-24
2007-11-15

So roughly 700 years since it was near the central star.

Neglecting any possible change in velocity, I come up with 701.4 years, confirming Art’s estimate.

So the next question I have is how old are the two lobes of this nebula? Is it even possible that these are anywhere as young as around 700 years? If not, then it would seem this has been a wild goose chase and this mystery object is just an ordinary passing star. But even if that is the case, (which is likely) this hunt has been both informative and fun.

Another question, is this object bright enough to be among the billion objects that the Gaia mission will measure?

[Chris Peterson]

Neglecting any possible change in velocity, I come up with 701.4 years, confirming Art’s estimate.

So the next question I have is how old are the two lobes of this nebula? Is it even possible that these are anywhere as young as around 700 years? If not, then it would seem this has been a wild goose chase and this mystery object is just an ordinary passing star. But even if that is the case, (which is likely) this hunt has been both informative and fun.

I'd think that the ejection velocity of the stellar gas shells would be at least several orders of magnitude higher than any reasonable velocity for an ejected star.

[geckzilla]

Another question, is this object bright enough to be among the billion objects that the Gaia mission will measure?

Not a clue, but the central star, which is the brightest star in the picture, is only 15th mag. I would guess no, if Gaia is looking for stars based on magnitude, which it appears to be. That's kind of a shame because while the overall structure of the galaxy is very interesting, I think any nearby star is also interesting simply for its proximity to us, even if it is a very dim star.

[BDanielMayfield]

I'd think that the ejection velocity of the stellar gas shells would be at least several orders of magnitude higher than any reasonable velocity for an ejected star.

Well alright! Since the gas blown out moves faster than our “runaway” object they still may have convergent histories. That’s wonderful. The game’s still afoot. Amazing, remote possibilities remain in play here.

But I doubt the runaway star notion more and more. I know that close encounters between stars are rare in most parts of space due to the vast average distance between them, but they’re not moving in parallel, so close encounters must occur at some very low rate. So what I was wondering about is; how might a close encounter between stars cause one of them to erupt a planetary nebula?

The only idea I can think of would involve a planet of either of the stars. We now know that most stars have planets as a by product of formation, and many stars have “hot” planets in tight orbits. My idea is that a close encounter between these two stars may have caused a planet to have collided with or been absorbed by the central star, and what we can see here today is the aftermath.

A planet may have been killed here, and Geckzilla’s Star may be fleeing the scene of the crime!

[Chris Peterson]

Well alright! Since the gas blown out moves faster than our “runaway” object they still may have convergent histories. That’s wonderful. The game’s still afoot. Amazing, remote possibilities remain in play here.

I was thinking that my observation largely rules it out, since the moving star appears to have a minimum distance from the star on the same order as the distance to the lobes.

So what I was wondering about is; how might a close encounter between stars cause one of them to erupt a planetary nebula?

People have examined what might happen if the Sun swallowed Jupiter, and the general belief is that nothing would change, it might not even produce a noticeable effect. Stars must swallow up planets numerous times in their early history, and it doesn't appear to do anything other than incrementally increase their mass. There is a brief window at the end of a red giant's life where it is extremely unstable, and its fusion rate is exquisitely sensitive to temperature. Maybe if it was struck by a planet at precisely that time, it might trigger the runaway reaction that creates a planetary nebula. But think about it. That would require a star that's doing exactly what this one is doing: displaying a proper motion aligned with the nebular star, but it would also require perfect timing. Statistically, that's far more unlikely than simply seeing a star with a proper motion vector pointing towards another, unassociated star. You could find thousands of examples of the latter. The only thing that makes this one notable is that both stars are in a fairly narrow field of view.

[Beyond]

Gee, Bruce, you seem to have the makings of a 'stellar' murder mystery.
Although Chris' post (who just beat me) would seem to make it a fictional one.

[BDanielMayfield]

Another question, is this object bright enough to be among the billion objects that the Gaia mission will measure?

Not a clue, but the central star, which is the brightest star in the picture, is only 15th mag. I would guess no, if Gaia is looking for stars based on magnitude, which it appears to be. That's kind of a shame because while the overall structure of the galaxy is very interesting, I think any nearby star is also interesting simply for its proximity to us, even if it is a very dim star.

Geckzilla, I’m shocked. To read you moaning about the limitations of Gaia! Words fail me …

During its mission lifetime of nominally 5 years, Gaia will scan the entire sky repeatedly, observing all sources brighter than 20th magnitude. The number of times that a single source is observed depends on its position in the sky, but on average Gaia will have provided 70 photometric measurements for an object at nominal mission end. Gaia's photometric and astrometric instruments will determine the object's brightness in several bands over the wavelength range 320-1000 nm.

That is from the Gaia website. I had to hunt around a lot to find it, since it was several pages in under Mission Science – Stars – Variable Stars.

If it achieves its goals Gaia will be the most informative mission to date (exclamation point)

[geckzilla]

The mission is simply designed to measure stars based on their brightness measured in Gaia magnitudes (I'm not entirely sure what a Gaia magnitude is) rather than by distance. I don't even know if sorting the stars by distance is feasible. It's more of a complaint about how there are some things that we'll just never know for sure. Just thinking about all of the variables to be considered and how accurate the measurements have to be hurts my head. Anyway, you may stow your shock. I have nothing but respect for Gaia.

[BDanielMayfield]

Well alright! Since the gas blown out moves faster than our “runaway” object they still may have convergent histories. That’s wonderful. The game’s still afoot. Amazing, remote possibilities remain in play here.

I was thinking that my observation largely rules it out, since the moving star appears to have a minimum distance from the star on the same order as the distance to the lobes.

I had to think hard (ouch) before completely understanding this statement Chris. But I see your point. The gas must be moving much faster than the (moving) star, but they appear to be at like distances from the central star. But as you know we’re looking at a 2D image of a 3D reality. We have to imagine depth here. What if the moving star is moving at close to a right angle to our line of sight, which would make its true velocity relative to the central star close to what Art calculated, “only 73 km/s”, while the gas lobes could mostly be directed toward and away from us, so they could have velocities significantly greater than what first appearance suggests.

The right lobe is brighter and smoother looking than the left. I think the right lobe was fired toward us and we might be seeing the top of a shock front here. On the other side we might be looking underneath a receding lobe and so we can see more lumpiness.

So what I was wondering about is; how might a close encounter between stars cause one of them to erupt a planetary nebula?

People have examined what might happen if the Sun swallowed Jupiter, and the general belief is that nothing would change, it might not even produce a noticeable effect. Stars must swallow up planets numerous times in their early history, and it doesn't appear to do anything other than incrementally increase their mass. There is a brief window at the end of a red giant's life where it is extremely unstable, and its fusion rate is exquisitely sensitive to temperature. Maybe if it was struck by a planet at precisely that time, it might trigger the runaway reaction that creates a planetary nebula. But think about it. That would require a star that's doing exactly what this one is doing: displaying a proper motion aligned with the nebular star, but it would also require perfect timing. Statistically, that's far more unlikely than simply seeing a star with a proper motion vector pointing towards another, unassociated star. You could find thousands of examples of the latter. The only thing that makes this one notable is that both stars are in a fairly narrow field of view.

This made perfect sense (darn it, but thanks), and I have no points to counter with.

I will however look forward to more data about this nebula and the mystery star in the years to come. Geckzilla mentioned that the central star is magnitude 15, what might the estimated brightness of the moving star be? Is it under the Gaia limiting magnitude of 20?