What is this object?

[geckzilla]

When I do processing for Hubble objects I often use data from several years apart. I see a lot of things that move slightly, like planetary nebulas expanding and more noticeable things like puffs of gas from HH objects. Parallax causes slight movement of stars sometimes. This one moved a lot more than things I've previously noticed, though. A whole three pixels. Usually things stick to the sub-pixel movements.

Anyway, these images are from observations of NGC 2371. The hover images are both WFPC2 data and they are 12 years apart, the first being from 1995 and the second from 2007. I'm sure it's not some kind of artifact. It's also present in some raw ACS/WFC data from 2009 which I'm not sure whether it's corrected for geometric distortion but I included the image anyway with it lined up as best I could. Not a lot of movement between the 2007 and 2009 observations.

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. I'm sure the HLA is full of hopelessly dim little oddities like this.

WFPC2

Click to view full size image 1 or image 2

ACS/WFC

[Beyond]

One of those single wandering stars??

[wonderboy]

doesnt look to have moved, unless im missing something!

[geckzilla]

It's the little dot in the lower left part of the frame. The main star of the nebula is kind of pointing to it in the hover image.

[neufer]

doesnt look to have moved, unless im missing something!

Geckzilla's first image is an overlay with which you can move your cursor back & forth to see the movement.

What is intriguing is that the star movement is away from the central star just as
if the formation of the strange nebula had ejected enough material to release an orbiting star.

[geckzilla]

It'd have to be moving very quickly if it's something local to NGC 2371! Much faster than the material in the nebula itself, which can also be observed expanding slightly in the mouseover set.

[neufer]

It'd have to be moving very quickly if it's something local to NGC 2371!
Much faster than the material in the nebula itself, which can also be observed expanding slightly in the mouseover set.

Faster than the material in the nebula currently
but not faster than the nebula over it's lifetime since it still lies inside the nebula.

I admit that it is a long shot but it is curious nonetheless.

[Chris Peterson]

When I do processing for Hubble objects I often use data from several years apart. I see a lot of things that move slightly, like planetary nebulas expanding and more noticeable things like puffs of gas from HH objects. Parallax causes slight movement of stars sometimes. This one moved a lot more than things I've previously noticed, though. A whole three pixels. Usually things stick to the sub-pixel movements.

Anyway, these images are from observations of NGC 2371. The hover images are both WFPC2 data and they are 12 years apart, the first being from 1995 and the second from 2007. I'm sure it's not some kind of artifact. It's also present in some raw ACS/WFC data from 2009 which I'm not sure whether it's corrected for geometric distortion but I included the image anyway with it lined up as best I could. Not a lot of movement between the 2007 and 2009 observations.

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. I'm sure the HLA is full of hopelessly dim little oddities like this.

I'm more curious about the streak from the bright star pointing towards your little moving object. And do you have links to the FITS files? JPEGs aren't very amenable to analysis.

[geckzilla]

Oh, the streak is one of the more annoying anomalies common for WFPC2 data. Any bright point source gets a kind of comet-like tail in the readout direction. See page 25.
Or, if you don't want to download a whole PDF, a quick, single sentence explanation here. (point number 10)

Due to declining charge transfer efficiency (CTE), bright objects and artifacts (e.g. stars and cosmic rays) may have prominent comet-like tails of deferred charge in the anti-readout direction.

Here are the FITS files.
http://www.geckzilla.com/astro/NGC2371.rar

List of files inside:

1995 / Bond (6119 is the proposal ID)
hst_06119_08_wfpc2_f555w_pc_sci.fits
hst_06119_08_wfpc2_f555w_wf_sci.fits

2007 / Noll
hst_11093_03_wfpc2_f555w_wf_sci.fits

2009 / Wade (This is the raw one. Nicer resolution, though)
jb5724020_drz.fits



Additional FITS files and of course individual exposures are also all immediately available through the HLA simply by typing NGC 2371 into the search box.

[Chris Peterson]

Oh, the streak is one of the more annoying anomalies common for WFPC2 data. Any bright point source gets a kind of comet-like tail in the readout direction.

Ah. I understand this characteristic of CCDs very well. I overlooked that the mouseover image was a rotated composite, so the angle of the smear is what got my attention. Now I see it is lined up with the physical array, and so makes sense.

[BDanielMayfield]

What is intriguing is that the star movement is away from the central star just as
if the formation of the strange nebula had ejected enough material to release an orbiting star.

Is it possible that Art’s suggestion is correct, that this is a former part of the star system which has been released?

Wikipedia lists the distance to NGC 2371 as being 4400 light years. How much distance would “three pixels” equate to?

[geckzilla]

Well, a WFPC2 pixel is 0.0455" wide so I guess you could throw 4400 in for two sides of a triangle and 3.7917×10^-5° for your one angle and figure that it moved 0.0029118 light years over about 12 years but it's all so much guessing...

[Chris Peterson]

Well, a WFPC2 pixel is 0.0455" wide so I guess you could throw 4400 in for two sides of a triangle and 3.7917×10^-5° for your one angle and figure that it moved 0.0029118 light years over about 12 years but it's all so much guessing...

I'd guess it's just a foreground star. A proper motion of 11 mas/yr isn't at all unusual- not even close to the fastest moving stars.

[neufer]

What is intriguing is that the star movement is away from the central star just as
if the formation of the strange nebula had ejected enough material to release an orbiting star.

Is it possible that Art’s suggestion is correct, that this is a former part of the star system which has been released?

Wikipedia lists the distance to NGC 2371 as being 4400 light years. How much distance would “three pixels” equate to?

Well, a WFPC2 pixel is 0.0455" wide so I guess you could throw 4400 in for two sides of a triangle and 3.7917×10^-5° for your one angle and figure that it moved 0.0029118 light years over about 12 years but it's all so much guessing...

Just 73 km/s

It could well be a runaway star then, IMO.

[geckzilla]

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

[neufer]

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

• Do what?

Alexander By Plutarch
Translated by John Dryden

<<[Alexander the Great] was naturally a great lover of all kinds of learning and reading; and Onesicritus informs us that he constantly laid Homer's Iliads, according to the copy corrected by Aristotle, called the casket copy, with his dagger under his pillow, declaring that he esteemed it a perfect portable treasure of all military virtue and knowledge.>>

[rstevenson]

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

[geckzilla]

Do what?

Figure out how far the stupid little blip is, even though it's probably completely mundane.

[Chris Peterson]

Do what?

Figure out how far the stupid little blip is, even though it's probably completely mundane. :)

No amount of astrometry can determine that. At best, it can place bounds on the distance- in this case, such wide bounds as to be practically useless. More information is required than just the proper motion.

[geckzilla]

Aw.

[Chris Peterson]

Aw.

However, had you actually slept on that astrometry tome, you'd know that. :)

[Beyond]

Hey Chris, how'd you sneak that key-board smilie past the computer Every time i type : and add )... it gives me this

[neufer]

Do what?

Figure out how far the stupid little blip is, even though it's probably completely mundane.

Have a question about Hubble or the astronomy Hubble studies?

[geckzilla]

Hey Chris, how'd you sneak that key-board smilie past the computer Every time i type : and add )... it gives me this

He has "Disable smilies" checked in the Options box below the full editor.

[Beyond]

Ah... never thought of that. Thanks, even if i don't remember it. :)))))))