05/03/23 U.S. Naval Observatory 1

Current Statistics on Visual Double Stars

Brian D. MasonU.S. Naval Observatory

Vice President, IAU Commission 26

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Growth of the WDS

• The WDS has seen significant growth in the past decade, both in the total number of mean positions (measures, black circles) and number of systems (open circles).

• Due to the small number of measures per system establishing which are true binaries (physical systems) is possible only for a subset of pairs.

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but, uneven coverage

• While the mean number of measures per system is 7.3, the median is only 3.

• 1617 have orbits of varying quality, 2202 have common parallax and/or common proper motion.

• Some are certainly optical. 1164 have rectilinear solutions and 810 have mutually exclusive parallax and/or proper motion.

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Orbits of varying quality

• Orbits can range from the well observed and well defined to those which are very poorly determined.

• Even a curve, indicating Keplerian motion, with scant coverage can yield a solution where the important quantity 3log(a) – 2log(P) is often not grossly erroneous.

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What about the rest?

• Some just need continued vigilance at the appropriate observing cadence.

• Some need observations with specific techniques and/or telescopes.

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even optical doubles of value

• This is the linear fit to the double STF 23. Seen almost due North by F.G.W. Struve in 1825, the companion has moved southwest since then.

• The best proper motion here indicated with a red line is from Tycho-2 and deviates significantly from the historical measures.

• For this class of optical double, the relative proper motion from double star measures will be superior.

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indicator of Keplerian motion

• Submotion seen in a more distant optical component can indicate a closer physical pair, in this case the known binary (incidentally the most often observed) 70 Ophiuchus.

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Sources of WDS data

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Statistics of WDS additions

Mean Median

% < 1” N < 0.1” N < 0.01”

1984 8.01 2.30 29.3% N = 943 (0.2%) 0

1996 12.62 1.68 41.1% N = 1670 (2.6%) 0

2001 10.71 1.87 32.2% N = 1230 (2.0%) N = 255

2006.5 26.26 10.11 9.7% N = 374 (0.2%) N = 34

current 27.43 9.36 17.9% N = 1296 (2.1%) N = 314

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Work by Amateurs on Neglected Pairs

• The C and D components of Polaris were observed by S.W. Burnham on the Lick 36” at the close of the 19th Century and not observed again until 2005 when Jim Daley recovered them. Many other large m systems still remain neglected.

• Historical measures of the AC, the AGK3, and others as well as more recent measures from 2MASS and Dave Arnold have allowed for this precise differential proper motion to be determined.

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Amateur Contributions

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Speaking to the Future

“The debt to our ancestors for the observations they

made to our benefit, we can pay only by doing the same for

our ancestors.”

Ejnar Hertzsprung, 1961