Neil Webster, REDACTED
E-mail : REDACTED
Introduction
The following measurements were made with a Meade 12-mm astrometric illuminated reticule eyepiece attached to a recently purchased Altair Astro 115-mm refractor (focal length 805mm, f7). The optical train also employed a 2.5x Powermate to give a total magnification of 167.5x. Calibration was achieved over two evenings using the timing transit method as outlined in Teague1 Three separate stars were used and the results (reassuringly close) averaged to give a calibration of: 12″.49 ± 0″.4 per division on the measuring scale.
Method
Earlier attempts with a smaller scope (SIV 80-mm APO) had indicated the necessity of taking multiple readings to achieve a credible result. Unless stated, each system has 10 separation and 10 position angle measurements (N 20) from which a final result and associated uncertainty were calculated. As expected the later results were, overall, found to be closer to \VDS values especially in P.A. Early P.A. values were made by turning the motor off and allowing the primary to drift and cross the, outer protractor scale. The scope was moved manually in R.A. to allow further measurements to be made. However, even with a relatively small system this was not easy and the following method was adopted:
With the motor on, the two stars were positioned parallel to the measurement-axis with the primary positioned to pass through the centre-point. The system was then steered to the outer scale using the R.A. control on the handset. The value that the primary passed through was noted and the appropriate conversion to the correct P.A. value made afterwards.
This has the advantage that repeated measurements can be, easily made and the scope can be easily slewed to the next system afterwards. The PA results were seen to immediately improve using this method. It, of course, relics on precise polar alignment of the mount so movement in declination is at an absolute minimum.
Duc to the small magnification of the, system the limiting useful minimum separation measurement is about 14″ . The accuracy of PA for small separations is also harder to achieve especially if the secondary is very faint. The faintest magnitude used for measurement was 10.3 due partly to local light pollution but also due to the obscuring rcd light used to illuminate the measuring eyepiece.
As most of these systems arc comparatively wide the orbits are, generally very long (30,000 years ) and very few have accurate orbital calculations. Residuals (from the online version of 6th USNO Catalogue of Orbits of Visual Binary Stars) have been given for the few systems calculated.
Residuals from the Fourth Catalogue of Interferometric Measurements have provided a more extensive set of residuals.
References
(1) Teague, E. T. H. (2012) in Argyle, R. W. (ed.), Observing and Measuring Visual Double Stars, Springer
(2) The Cambridge Double Star Atlas, (Mullany J. Tirion pub. Cambridge)
(3) Washington Double, Star Catalogue (Mason, B.D., Wy-coff, G.L. Hartkopf, w.l.):
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(4) http : // ad. usno . navy .mi1/proj/WDS
(5) Sixth Catalogue of Orbits of Visual Binary Stars (Hartkopf, NV.I., Mason, B.D. & Worley,
http : / /www.usno . navy . mil/USNO/astrometry/optical- IR-prod/wds/orb6/sixth- catalog-of-orbits-o (6) Fourth Catalogue of Interferometric Measurements of Binary Stars:
http : //www.usno . navy. mil/USN0/ astrometry/ optical-IR-prod/wds/int4