Up: Measurements of double stars 1998.13
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
. This value
was determined by timing transits
of circumpolar stars. As the thickness of the
tungsten wires is
resulting in an apparent thickness of
of the
wires, for some few close pairs a Barlow lense
was used giving a screw value of
and an apparent thickness
of the wires of
. 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
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
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
diffractionmeters, for pairs from
to
the
distances were estimated by applying various diaphragms until the stars were
just separated. Distances
below
are estimates with full aperture, as a
rule.
For larger magnitude differences a
diffractionmeter with
producing
satellites
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.
Up: Measurements of double stars 1998.13
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