Star Puzzle

[petevasey]

Hi, all,

The image below is a full size crop from my image of the mag 10 galaxy NGC 3198 in Ursa Major.  Practically overhead during the night so a good target this time of year.  As you will see if you visit my web site it is really a work in progress and I hadn't intended to post it here yet.   But a bit of a puzzler.  As you can see there appears to be a double star just above the galaxy.  It's listed in Skymap, Stellarium and SkyX as mag 11.2 GSC3435-470.  But zoom in, only in SkyX it is then shown as a triple star - screenshot below.  The left hand smaller star is listed as mag 12.83 UCAC3 272:113377, the right hand smaller star as mag 12.7 UCAC3 272:113375.  I've scrabbled around to try and find an image further resolving the star, but the ones I've found only show it up as a similar brightness double.

Can anybody cast light on this?

Cheers,

Peter

[vlaiv]

Try to see if stars could match the image above.

Inspect their distance in arc seconds to see if they can be resolved in your image and also inspect their magnitudes. If one of the three is significantly less bright - system will present as double star (especially if they are close and weak one is the middle one).

Maybe try to resolve the system yourself? Try by using lucky imaging approach - sample at critical sampling rate with narrowband filter and very fast FPS. Stack in planetary software like AS!3 and use wavelets (carefully) to sharpen things and see if you can split the system.

[petevasey]

According to SkyX the spacing betwen each star is 2", i.e. 4" between the smaller stars.  So with a Barlow it might be possible to resolve better.  But with the end stars being relatively faint 'lucky' imaging won't be that easy - I'll probably need a few seconds per frame.  Certanly worth a try!

Cheers,

Peter

[petevasey]

I've had another look at my image and the SkyX information, and comparing the magnitudes with nearby stars I now believe that there are only the two outer stars , and the GSC is essentially the two combined.  Not a very good one for Hubble to use - with a spacing of 4 arc-secs the accuracy would have been compromised!   My image above doesn't show the indicated star in the different crop below, but  that star is listed as mag 12.4 - just slightly brighter than the individual stars in the double.  Also I've slightly improved the resolution of the double, and clearly there isn't a brighter star between the two - a third diffraction spike would have been obvious.

Cheers,

Peter

[Whirlwind]

I wouldn't worry about it too much.  There are a lot of catalogues out there and photometry and astrometry has used more developed code (and better resolution images) over time.  Hence old catalogues might have identified the object as one star but later as two stars - which is why you now see it in such programs as three stars when you load multiple catalogues.  

The Gaia catalogue is the best source of data these days.  This shows only two days.  They are about 842pc (+/- 26pc assuming three sigma error) and 884pc (+/- 29.7pc assuming a three sigma error).  Their proper motions are also very similar so there is a good possibility this is a binary system but longer observations are really needed to be conclusive.