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Somebody give this star a speeding ticket.

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8 years 8 months ago #72424 by DaveGrennan
Tonight I was blinking some galaxy images acquired this evening with digital sky survey references images searching for supernovae. I had a few images I ignored because some high cloud made them a bit too noisy. Anyhow when I had exhausted all the good images I went back to the grainy ones. Nothing too strange to report except;

On the very last image I noticed what looks like a star with a very high proper motion compared to other stars. Take a look at the animation below and look at the star marked on the left. Look how it changes position when compared to the DSS image. The DSS image is from the POSS-II survey which was taken over the period 1987 - 1998 so its hard to put a timestamp on that image (I'm sure I can find out). But even given the earliest date the proper motion of that star must be huge to show up so noticably. A little more research is needed methinks, but first sleep zzzzzzz.

Here's the animation;


Regards and Clear Skies,

Dave.
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8 years 8 months ago #72425 by Vagelis Tsamis
Interesting, Dave.
Can you give us more info? What's that galaxy and FOV?

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8 years 8 months ago #72428 by JohnMurphy
Could it just be an edge of field distortion?
It would be nice to get that star more central in the FOV and then do a comparison with DSS.
The weather is supposed to improve toward the end of the week - particularly Friday. See if you can duplicate the same result with fresh data and clean skies, then you may be on to something. :unsure:

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8 years 8 months ago #72435 by DaveGrennan
Vagelis Tsamis wrote:

Interesting, Dave.
Can you give us more info?


Do the Greeks like astronomy?:laugh:

The galaxy in question is PGC 68197

Well I did lots more research on this tonight. The star in question is indeed a High Proper Motion star. The star itself resolves in Simbad as UCAC2 46198582.

Its listed in the LHS catalog of HPM stars as LHS6397. It lists as having the following PM;

PMRA 418 milliarcsec/yr
PMDEC 240 milliarcsec/yr

My own measurements seem to contradict this. I discovered (from the FITS header) the POSS plate was taken on 1989-09-04 so almost 19 years ago.

I carried out an astrometric analysis and discovered the following
DeltaA (Diff in RA) = .73"
DeltaD (Diff in Dec) = 3.68"

This thus corresponds to;

PMRA = 38.42 mas/yr
PMDEC = 193.68 mas/yr

The animation posted earlier was just a crop from the full image. Here's a better animation with the star off the edge;



This has given me a whole new idea for a little research project. To measure the proper motions of say the top 100 highest PM stars in the northern sky. Now that would be a lot of fun.

Regards and Clear Skies,

Dave.
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8 years 8 months ago #72442 by dmcdona
Nice work Dave - interesting that your calculated motion is different from LHS - certainly the DEC PM is close, but the RA PM is very different...

Definitely an eighty quid fine...

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8 years 8 months ago - 8 years 8 months ago #72446 by Vagelis Tsamis
Good job, Dave!

I also checked at Simbad and Aladin: This little beautiful star is a spectral type M 3.5 main sequense dwarf. It has a red color, as u can see at Aladin image http://aladin.u-strasbg.fr/alapre.pl?-c=22+09+43.05%2B41+02+05.6&button=RGB
It's amazing to see the star's energy fluxes in dif. parts of light spectrum in the Simbad page!
And it is in the "nearby stars" list.
How close is it to the Sun? I am not exactly sure which data I should look for.

Vagelis

Sparta Astronomy Association / Observations Coordinator
International Occultation Timing Association / European Section, www.iota-es.de/
Last Edit: 8 years 8 months ago by Vagelis Tsamis.

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8 years 8 months ago - 8 years 8 months ago #72447 by bertthebudgie
Wow what a find dg. I wonder would the difference in proper motion due to the fact that the dss image was taken in April and yours in August thus adding the Earths orbital movement to you calculation?.

I mean as it is a nearby star could it be the stars paralax you are measuring rather then its true proper motion. Means you need to take another image in 6 months to be sure:)

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8 years 7 months ago - 8 years 7 months ago #72483 by JohnMurphy
Nice result DG. Nice research Vagelis (say hi to Kiriakee for me, and of course all the gang - missing you all - hope to see you next June).
DeeBee - Parallax would affect all stars in the field thereby negating any differentiation. Think of it this way - there are many stars in the field, incl. galaxies with widely different distances from earth, yet they show no apparent movement. Unless the star in question is very close we should see no discrepancy

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8 years 7 months ago #72497 by bertthebudgie
You are correct. But I understand that this star is very close to us.

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8 years 7 months ago #72568 by cobyrne
Dave Grennan wrote:

I carried out an astrometric analysis and discovered the following
DeltaA (Diff in RA) = .73"
DeltaD (Diff in Dec) = 3.68"

This thus corresponds to;

PMRA = 38.42 mas/yr
PMDEC = 193.68 mas/yr

Are you sure you did your calculations correctly? It looks to me as if the star is moving more in RA than it is in DEC. Did you remember to multiply your RA seconds by 15 to convert to arc seconds? That would have given you 576.3 mas/yr - 38% more than what simbad gives, but at least the right order of magnitude.

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8 years 7 months ago #72574 by cobyrne
The parallax of the star is given in SIMBAD as 44.4 mas plus-or-minus 3.3 mas.

So it's distance from us is 1.0 / 0.0444 = 22.5 parsecs = 73.4 light years (plus-or-minus 5.5 light years).

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8 years 7 months ago #72576 by DaveGrennan
You are spot on Chris. Thats exactly what I did.

I had forgotten to convert it to angular degrees. The correct value should be therefore;

.73 * (15 * cos(41)) = .73 *11.3206 = 8.2641" which equates to a PMRA of 435mas/yr. This is much closer to the published value.

Regards and Clear Skies,

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