[vsnet-chat 759] Position of NGC 5128-V17

[bas@lowell.Lowell.Edu (Brian Skiff)]

     I found a few plates of NGC 5128 taken by Carl Otto Lampland in the
Lowell Observatory plate vault.  They were taken some 80 years ago with the
observatory's 1.1-m f/5 Newtonian (~37"/mm) located on Mars Hill.
     I have measured the star V17 and CoD-42 8389 as well as two others stars
superposed on the galaxy on two plates.  I used our venerable PDS machine and
a reference net of twelve PPM stars (including PPM Supplement stars).  The
mean residuals from a quadratic fit to the reference stars were ~0".1 in RA,
but about 0".5 in Dec.  I suspect this results from an incomplete compensation
for differential refraction in the solution (severe since the plates were
inevitably taken at high zenith distance).  No matter---this is a lot better
than what is evidently available for the stars!
     The average values are listed below, rounded to 1" precision.  Star "A"
is the bright star in the dark lane of the galaxy, near its geometric center.
Star "B" is the somewhat fainter star lying between V17 and the 'central star'
in a small dark patch south of the main rift.


                 RA  (2000)  Dec
CoD-42 8389   13 25 27.7  -43 02 17

V17           13 25 28.5  -43 02 05

A             13 25 23.8  -43 00 53

B             13 25 24.9  -43 01 28

For what it's worth, the positions are for the mean epoch of the plates, about
1917.9, but I'm sure any systematic errors from the imperfect net and 
reduction dominate any proper motion for these stars.
     There was really no challenge in measuring these stars, but it merely
required having a convenient original plate and a measuring machine.

\Brian

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