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High Proper Motion Star imaged. (By Accident)

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Author Topic: High Proper Motion Star imaged. (By Accident)  (Read 771 times)
davegrennan
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« on: August 26, 2008, 12:34:18 am »

Last night I was carrying out a supernova survey.  Unfortunately the dreaded clouds rolled in before I got too many galxies imaged. While reviewing the images I noticed that one star in particular was at a very different position to the Digital Sky Survey reference image.

The following animation demonstrates;



Anyway tonight I did some more research on it.

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

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.
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Regards and Clear Skies,

Dave.
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J41 - Raheny Observatory.
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brianb
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« Reply #1 on: August 26, 2008, 08:52:37 am »

Very interesting.

I respectfully suggest you recheck your figures. Your total displacement of just under 4 arc sec seems to be on the small side, I'm amazed you're getting that resolution on the image given normal seeing conditions! There isn't for instance a confusion between seconds of RA  and angular arc seconds? 1 sec RA = approx. 15 arc secs. at the equator; multiply by the cosine of the declination elsewhere.  Your figure of 194 mas/yr in Dec is "close enough" to the catalogue value of 240, and with a correction factor of x10 assuming the Dec of the field around 50 degrees the RA figures could match fairly closely as well. This would also push out the total displacement between the images to ~10 arc sec which seems rather more believable.

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davegrennan
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« Reply #2 on: August 26, 2008, 02:04:48 pm »

Brian I think you are correct about the RA figure.  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.

The software I use for astrometric analysis (pinpoint) can estimate down to 1/10 sub pixel.  The pixel scale above is 1.8" pixel.  Thus the coordinates can be accurate to .18".  Since in such long exposures the seeing thends to average out, reported positions are normally right on the mark.  For example the average residuals from observations I submitted to the minor planet centre last year was .21"(RA) .23"(Dec)

Many thanks for pointing this out to me.  Much appreciated.
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Regards and Clear Skies,

Dave.
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martinastro
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« Reply #3 on: August 26, 2008, 02:55:06 pm »

That is a real gem Dave. Great to see some good scientific observing being done!. I never knew a HPM star could be detected like that. Very impressive work. Supernova searching looks to be a very exciting way to learn the sky, especially when you make other discoveries along the way like this one. Excellent stuff. Thanks for sharing!  Smiley

What are the names of the two primary galaxies?
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brianb
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« Reply #4 on: August 26, 2008, 04:02:48 pm »

Quote
Many thanks for pointing this out to me.  Much appreciated.
You're welcome.

Did you notice that the slightly fainter star immediately to the lower right of the "wanderer" has a proper motion too, and it seems to be in approximately the same direction though a lot smaller in size? Might there be a physical association?

Also, if you look at the top of the frame, there are three "bright" stars forming a right triangle with a fourth "bright" star more or less in a straight line with the middle length line extended a bit. The middle one of the stars in this line also seems to be displaced on your image, but to the left rather than to the lower right.

Maybe about time someone redid those DSS frames!

I understand what you're saying about the derived position being to sub-pixel accuracy, and seeing "averages out" so that accurate positions can be obtained even in poor seeing. My original suspicion about your numbers was based on surprise that images, which will be showing stars around one arc second across even in excellent seeing (the professionals do no better without interferometry and/or adaptive optics) were nevertheless showing "clear space" between the two positions of the star, it just felt wrong for a displacement of about 4 arc sec.

Found any asteroids or comets yet? I think those people who go supernova hunting usually do!

All the best and keep up the good work!
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davegrennan
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« Reply #5 on: August 26, 2008, 10:56:51 pm »

Found any asteroids or comets yet? I think those people who go supernova hunting usually do!

All the best and keep up the good work!

Not yet Brian.  At least none that haven't already been found.  The problem with asteroid discoveries is that the big surveys like LONEOS and LINEAR have swept up the vast majority of the bright ones.  Most asteroids are not discovered around mag +20 thats a little too faint for my setup. (I can get to around mag 18.5 on a good night)  I hope to improve on this with the acquisition of a more sensitive CCD and improved techniques.  Time will tell.  For now supernova surveys and minor planet astrometry is what ill be at.  In the not too distant future I hope to try my hand at recording transiting exoplanets.  I hope to assist Eamonn Ansbro with some of the wonderful work he is doing in research he is doing.

A supernova discovery would be just great though:)
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Regards and Clear Skies,

Dave.
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davegrennan
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« Reply #6 on: August 26, 2008, 11:04:12 pm »

What are the names of the two primary galaxies?

Thanks Martin,  the galaxy at left is UGC 11927 (PGC 68171) (mag +14.4) and the one at right is NGC 7223 (PGC 68197) (mag +12.2)

I forgot to mention why the galaxies are so dim in my image.  That was the last image collected before the clouds rolled in, the image was taken through a layer of high cirrus cloud which preceeded the lower level fluffies.
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Regards and Clear Skies,

Dave.
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J41 - Raheny Observatory.
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Equipment List here
martinastro
Martin Mc Kenna
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« Reply #7 on: August 27, 2008, 02:09:09 pm »

Thanks very much for the galaxy info Dave. I must look those guys up for further data. I had a feeling high level cloud had rolled in for the last image, but even so, you still picked up the core of that very faint 'lenticular' galaxy beside NGC 7223!!. I'm certain you will discover a comet or supernova during your search in the future  Wink

I was interested to know why you targeted these two galaxies for a supernova patrol. Was it because Lacerta was high in the sky away from poor sky conds, or do these two spiral galaxies have a history of supernova explosions?. Are these part of your nightly patrols or were they the exception to your patrol list?...just curious Smiley

Cheers
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davegrennan
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« Reply #8 on: August 27, 2008, 11:20:27 pm »

I was interested to know why you targeted these two galaxies for a supernova patrol.

Good question Martin.  The answer is down to the way I select galaxies for search.  Each night (or more often periodically) I choose an area of sky which is well placed.  At the moment the area around Pegasus and North of it are well placed (including Lacerta).  I have created a database from a couple of cross referenced galaxy catalogs.  The primary database is the PGC catalog.

From over 100,000 galaxies in my database, I start filtering by predetermined criteria.  So any galaxies outside the target area are ignored.  I then rule out objects fainter than I can image.  I'm still left with a couple of thousand.  So I then rule out ellipticals, irregulars (i.e favouring spirals which are more likely to produce supernovae).  I'm usually still left with a good few hundred targets.  I then favour more northerly galaxies since this is where the big surveys (LOSS, puckett etc) are less likely to be looking.  If more than 100 targets are left I just get tighter on the magnitude filter until I'm left with about 100.  These are then output to a script which is then uploaded to the observatory for imaging.  All going well I come back a few hours later and begin searching through the images.

Unfortunately I rarely get to get all 100 images because cloud invariably rolls in.  I'm looking forward to getting one of those 'clear from dawn to dusk' winter nights.  I reckon I might be able to do 250 galaxies in one of those nights all going well.

What I like about the supernova searching is that even an unsuccessful search produces lots of cool looking galaxies and occassionally something interesting like this HPM star.
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Regards and Clear Skies,

Dave.
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J41 - Raheny Observatory.
http://www.webtreatz.com
Equipment List here
martinastro
Martin Mc Kenna
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« Reply #9 on: August 28, 2008, 10:54:48 pm »

Thanks very much for the detailed reply Dave. That's a good stragety you have. I hope you get many of those dusk to dawn Winter nights this year. The hunt sounds extremely exciting.  Smiley
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