[vsnet-alert 4480] Re: (fwd) SN suspect in NGC 5128

["Berto Monard" <LAGMonar@csir.co.za>]

Dear Hitoshi and readers,

I have the feeling that we are trespassing the -alert channel with this discussion but for completeness (hopefully) I like to keep this final reply on the same track.

In order to answer the query I have to again rely on my fading memory but this time with a close look at a detailed Cen A chart, courtesy of A Wassilieff. 

Hitoshi, they are not correct, neither was I in my previous posting.

In the assumption that Cen A is located at (2000) 132526.4-430106 (Simbad), the coordinates for CoD-428389 and star 'A' coincide reasonably well with the positions of the 11 and 12.5 magnitude stars respectively. I must have made an error in locating  the 12.5 star in a previous posting (without having looked at a proper chart and for which I apologize). 
Possibly V17 coincides with the faint star NNE of CoD.. but is distinctly fainter than 14.5. I still doubt if it is variable. 
Star 'B' is around magnitude 14.5 and the other 14.5 magnitude star is about 30" West of CoD and about 50" South of star B... 

Sorry about the confusion, your deduction that star B was = the 12.5 star was sound but unfortunately based on incorrect information ie my erroneous description of its position... 

In the true sense they are all foreground stars to Cen A.

Best regards,

Berto


>>> Hitoshi YAMAOKA <yamaoka@rc.kyushu-u.ac.jp> 03/27/00 01:22PM >>>
Dear Berto and all,

>The 11th magnitude star is indeed visible on your nice picture, just
>under (South of) the centre of the Southern bright starforming
>region.  The 12.5 star is not obvious and is located just South of
>the centre of the galaxy, just under the dust lane.  The two 14.5
>stars are in the region between the two described foreground stars,
>one is visible just NNE of the brightish 11th magnitude star.

  From my archive of vsnet-chat, there was some nice identifier of
this region given by B. Skiff (2 years ago).  For the reference, I
reproduce it below.  The "mag 11 star" would be CoD-42 8389, "the 12.5
star" would be star B.  Visible 14.5 star would be NGC 5128-V17.
Are they correct, Berto?

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan
yamaoka@rc.kyushu-u.ac.jp 

>Date: Wed, 11 Mar 1998 04:16:32 -0700
From: bas@lowell.Lowell.Edu (Brian Skiff)
Subject: [vsnet-chat 759] Position of NGC 5128-V17

     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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