[vsnet-chat 2150] Re: Missing CoD stars

[Mati Morel <morel@ozemail.com.au>]

        Over the last 25 years, in the process of preparing finder charts
for the VSS, RASNZ, involving hundreds of variables, I commonly plotted CoD
stars (and CPD stars) in the respective fields. Usually a 1-square degree
chart would be prepared almost entirely
from a CoD plot, giving a satisfactory amount of detail. Such a chart would
contain
from 60-100 stars, more or less.  I found that in such a sample of stars,
there would
generally be at least one "problem" star (I hesitate to call them "missing"
stars, as this tends to make a presumption, prematurely). A problem star is
one that cannot be
found at its nominal position, initially. At first glance such a star
appears to be
missing, but upon closer examination some sort of rational explanation
usually comes
to mind. Whether my own explanation is the correct one is another matter.
        I came to expect each 1-degree field to present at least one problem
star. 
Explanations were generally found, while many of these stars would in
earlier times
have been described as "missing".  I give a few examples below.

BL Vel field.
CoD-46 3785 (10).  Nothing at this spot. Prob. positional error. Perhaps
identical
with nearby CPD star.
BK Vel field.
CoD-43 3925 (10). Nonexistent. Probably a different observation of -46 3927.
UU Pyx field.
CoD-31 6853 (9.9). Missing. Later recovered, to NW. High pm DA6 star. V = 11.90.
AG Hya field.
CoD-23 8798 (9.4). Missing? Probably duplicate observation of -23 8800.
T Pyx field.
CoD-31 6853 (9.9). Missing. Probably duplicate observation of -31 6851.
DW, FP Vel field.
CoD-51 4274 (10). No bright star at CoD posn.
CoD-51 4288 (10). Nothing at CoD position, but prob. id. with FP Vel, 6.8s
preceding.
FP Vel is a Carbon star, V=10.51.

I have found numerous cases of duplicate observations, and most of them
apparently
never documented. While there seem to be a lot of missing CoD stars (one per
square
degree of sky is no exaggeration), most of them can be resolved one way or
another.
Some cases do require a bit of time and effort, making comparisons with other
datasets.  This is the main problem with the CoD - many of the faint-end
stars have
have never been properly validated, so one cannot always be sure what was
actually
observed.
Regards,

 












/Mati

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