[vsnet-chat 2611] CGCS - SAO Cross Index

[JG <jgts@jgws.totalserve.co.uk>]

[NB this message keeps bouncing back from my ISP.  If more than this
copy got through, my humblest apologies!!!!!!!!]


Thanks to advice given in VS-chats 2607 and 2608, I was able to get my
mindset in order!

A _complete_ cross Index of the entire CGCS and entire SAO at three
decimal degrees in RA and DEC [36 arcsecs resolution] gives 22 common
objects.  Note that, throughout, the SAO has been used to 'sample' old
spectral classifications for these stars.  Further, as the precision of
the CGCS co-ordinates is somewhat dependent upon the identification of
the object in other studies, the list is biased towards better known
objects, ie ones which would have been _known_ to be variable stars
during the SAO compilation.  eg FK Pup=CGCS 2082 was _not_ cross-linked
with the SAO at this resolution.

Of these 22 stars common to both catalogues at 36" resolution, 2 are R
type stars and 17 are N type stars, ie of Carbon Star spectral types,
consisting mostly of known variables.

The remaining 3 are:

CGCS 798 = SAO 195328 = M;  CGCS 1911 = SAO 174678 = A3;  CGCS 2792 =
SAO 251015 = F0

Note CGCS 798 reappears, and Mati Morel's SAO 251015 also reappears.
The historic uncertainty of FK Pup's identification seems to be
reflected in it not passing this '36 arcsec resolution' test, as neither

does CGCS 777.

CGCS 1911 is _very_ closely superposed upon SAO 174678, and A3 is a very

strange spectrum for a star suspected of being a Carbon star!  Given a
quarter million fairly evenly distributed stars (as per the SAO remit),
what are the chances of any randomly chosen position coinciding with one

of them? A relatively bright star lies only 2' N.

Basically, however, the situation for F type Carbon stars appears to be
a one off! (2 off with FK Pup).  At least until more CGCS objects can be

identified with visual counterparts, etc.


By way of a 'control', I also assessed 1347 S stars from C B
Stephenson's General Catalogue of S Stars 2nd edition (Publ. Warner &
Swasey Observatory, 3, 1 [1984]) against the SAO.  [As with the 2nd and
first Carbon Star catalogues, ie the CGCS and CCCS, the 2nd S Star
catalogue = CSS 's numbering does _not_ tally with the 1st, the GCSS].
Stephenson again made use of objective prism plates from the Warner &
Swasey Obs. during compilation of this catalogue, so it is a 'crititcal'

compilation.

Of the 12 objects common to both the CSS and SAO at 36 arcsec
resolution, 5 are K5 or K7, 6 either M5, M6, Ma or Mb and 1 has no
spectral class listed in the SAO.

As S stars form a parallel spectral branch to stars in the K5 to late M
range, mostly distinguished by Zirconium Oxide bands and Technetium
lines, the above spectra seem reasonable if derived from low dispersion
surveys.



In general, confidence in a catalogue should be restricted to its
_primary_ data (and not always then, apparently)!  The SAO is an
astrometric catalogue, and a compilation.

A couple of years ago I investigated what difference it would make if
some binocular comparison sequences had their visual values replaced
with Tycho catalogue Johnson V values, and how that compared to the use
of ground based Johnson V values, etc.  Previously someone had
laboriously cross identified a very large number of these stars,
theretofore known only as dots on comparison charts, using planetarium
software.

Unfortunately they'd chosen to use the SAO as the identifier, a
catalogue rarely included as the cross identification in any photometric

catalogue, most of which follow the 'Laussane' convention, which will
mainly use HD identifiers or Durchmusterung identifiers for stars above
magnitude ten, where possible.

This led to phases of cross identification via various catalogues, which

can lead to extra chances of error (some of the cross ID catalogues
themselves contain errors)!

Hopefully, the Hipparcos and Tycho Catalogues, with their built in
rigorous cross IDs [hopefully updated as errors are found] will become
the main ID of choice for stars in this magnitude range in future.


Which reminds me: does anyone know the status of Tycho2, which was 'due'

about now?


Now, as previously promised, I hand back to the CVers!

Cheers

John

John Greaves, UK

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