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Old 2017-03-22, 20:59   #1
fivemack
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Default Double stars

Consider http://www.chiark.greenend.org.uk/~twomack/binary

DSC_0552, DSC_0549 and DSC_0553 are three exposures, taken 28/11/2016, of the field containing Uranus. Exposure times are about 0.2, about 1.8 and about 9.3 seconds.

If you look at 100% zoom you will see a great deal of coma, but also the double star ζ Psc, whose 23-arcsec separation has come out at 400mm focal length as about 6 pixels. The interesting image-processing question is whether you can convince yourself statistically that one of the stars in the image was a one-pixel disc rather than a point source before being convoluted up; unfortunately even in the 0.2-second image the brightest pixel in Uranus has saturated, though the double star shows very cleanly.

It looks like γ Leo and γ Vir would be appropriately challenging targets for this equipment (4.5" and 2.5" respectively); η Cas at 13" and ξ Boo at 7" might be a sensible run-up.

Last fiddled with by fivemack on 2017-03-22 at 20:59
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Old 2017-03-23, 14:33   #2
xilman
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Quote:
Originally Posted by fivemack View Post
Consider http://www.chiark.greenend.org.uk/~twomack/binary

DSC_0552, DSC_0549 and DSC_0553 are three exposures, taken 28/11/2016, of the field containing Uranus. Exposure times are about 0.2, about 1.8 and about 9.3 seconds.

If you look at 100% zoom you will see a great deal of coma, but also the double star ζ Psc, whose 23-arcsec separation has come out at 400mm focal length as about 6 pixels. The interesting image-processing question is whether you can convince yourself statistically that one of the stars in the image was a one-pixel disc rather than a point source before being convoluted up; unfortunately even in the 0.2-second image the brightest pixel in Uranus has saturated, though the double star shows very cleanly.

It looks like γ Leo and γ Vir would be appropriately challenging targets for this equipment (4.5" and 2.5" respectively); η Cas at 13" and ξ Boo at 7" might be a sensible run-up.
Good idea. I had already glanced at the images you gave me and thought there might be a possibility of finding a satellite or few. I hadn't thought about trying to resolve the disk.

I'll bring them closer to the front of the queue.
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Old 2017-03-23, 18:41   #3
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OT: The thread title reminded me of a Heinlein book, "Double Star." However, it does not concern astronomy, as such.
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Old 2017-03-24, 11:15   #4
fivemack
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Default Fun with data mining

Code:
http://ad.usno.navy.mil/wds/Webtextfiles/wdsnewframe.html
is the Washington Double Star Catalogue

Code:
awk 'substr($0,6,1)=="+"' < wdsweb_summ.txt | awk '{print substr($0,59,5),substr($0,65,5),substr($0,53,6),$0}' | awk '$3>5 && $3<10' | awk '$2!="." && $2<6' | less
is the set of binaries in the Northern hemisphere with a secondary brighter than magnitude 6 and a separation of 5 to 10 arc-seconds; you get coordinates (20457+1607 means 20 45 42 +16 07, the fifth figure is in tenths-of-minutes so multiply by six to get arc-seconds) rather than identifiers, but SIMBAD turns coordinates into names very happily.

I've missed gamma arietis and gamma andromedae, but pi bootis, zeta cancri (which is a triple) and zeta CrB are quite well-placed at this time of year.

Narrower separations ($3>2 && $3<4) : epsilon bootis, delta serpentis, mu draconis, epsilon-1 lyrae (part of the famous double-double). Mu draconis is conveniently circumpolar.

12 Lyncis is circumpolar, it's going to be non-trivial to find in the region between Capella and Ursa Major but is a nice triple (1.8" and 8.6")

Last fiddled with by fivemack on 2017-03-24 at 11:20
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Old 2017-03-24, 18:30   #5
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Quote:
Originally Posted by fivemack View Post
Code:
awk 'substr($0,6,1)=="+"' < wdsweb_summ.txt | awk '{print substr($0,59,5),substr($0,65,5),substr($0,53,6),$0}' | awk '$3>5 && $3<10' | awk '$2!="." && $2<6' | less
awk. How quaint. I thought I was old fashioned using Perl.
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Old 2017-05-14, 08:50   #6
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Quote:
Originally Posted by fivemack View Post
If you look at 100% zoom you will see a great deal of coma, but also the double star ζ Psc, whose 23-arcsec separation has come out at 400mm focal length as about 6 pixels. The interesting image-processing question is whether you can convince yourself statistically that one of the stars in the image was a one-pixel disc rather than a point source before being convoluted up; unfortunately even in the 0.2-second image the brightest pixel in Uranus has saturated, though the double star shows very cleanly.
A quick looks suggests that the task is likely hopeless. The focus is just too bad. There are also very nasty artefacts in the red channel, though the green seems to show primarily coma and/or astigmatism. Curiously enough, the FWHM of Uranus' radial profile plot is smaller than that of field stars of comparable brightness.

Oh well, I'll stick to photometry for the time being.
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