2 Instrumentation

The principal instrument is a 32.5 cm, f = 620.5 cm Cassegrain running on a heavy German mounting. Two micrometers were used:
A. A RETEL filar micrometer with a screw value of $16\hbox{$.\!\!^{\prime\prime}$}62 \pm 0\hbox{$.\!\!^{\prime\prime}$}01$. This value was determined by timing transits of circumpolar stars. As the thickness of the tungsten wires is $12~\mu{\rm m}$ resulting in an apparent thickness of $0\hbox{$.\!\!^{\prime\prime}$}40$ of the wires, for some few close pairs a Barlow lense was used giving a screw value of $6\hbox{$.\!\!^{\prime\prime}$}43$ and an apparent thickness of the wires of $0\hbox{$.\!\!^{\prime\prime}$}15$. Red field-illumination was used. At least 5 settings were made for one position angle measurement, at least 2 double distances were taken for one separation. Without Barlow the magnifications was 496, with Barlow 642.
B. A MECA PRECIS double image micrometer, type B. Lyot, using the principle of a rotatable iceland spar plate. The value $e/f = 0.000653 \pm 0.5\%$ with e = thickness of the spar plate and f = focal length of the telescope was determined by distance measurements of some of Mullers fundamental stars (all of them measured by Hipparcos), double stars with definitive orbits, Speckle measurements of wide pairs in the range of 2 arcsec. and many pairs having been measured by Hipparcos. The same number of settings - at least 4, mostly 6 or more - was made for the position angles and the distances. This micrometer was mostly used for pairs under 2 arcsec. Magnifications were normally 620, for some few faint pairs 388 and 496.

It must be emphasized, that the distances of pairs with separations below about $1\hbox{$.\!\!^{\prime\prime}$}5$ and brightness differences of not more than 1.5 mags are more accurate and very easily measurable with the double image micrometer.

The second instrument, a 360 mm, f=4.9 Zeiss-Newtonian, was used 1993.67 - 1996.50. The angles were measured with wires fixed in eyepieces, the latter rotatable on a position angle vernier. For the distances several methods were used: for bright pairs wider than $1 \hbox{$.\!\!^{\prime\prime}$}0$ diffractionmeters, for pairs from $0\hbox{$.\!\!^{\prime\prime}$}5$ to $1 \hbox{$.\!\!^{\prime\prime}$}2$ the distances were estimated by applying various diaphragms until the stars were just separated. Distances below $0\hbox{$.\!\!^{\prime\prime}$}5$ are estimates with full aperture, as a rule.

For larger magnitude differences a diffractionmeter with $z=1\hbox{$.\!\!^{\prime\prime}$}4$ producing satellites $2\hbox{$.\!\!^{\rm m}$}1$ fainter than the primary was very helpful for the distances and estimates of the magnitude differences. The magnification was 490 X, in few cases for close doubles 660 X. In this list one will find several stars in rapid motion neither measured by Hipparcos nor recently by speckle, for example STT159, STF1280 and STF2434BC.