[vsnet-chat 3601] UCAC, USNO, NSV 12041,chats 3598, 3599 & 3600...

[crawl@zoom.co.uk]

FIRST, and most importantly, the proper motion part of my previous mail was
not in trouble because of assumed USNO A2.0 plate epochs, but was valid
[however, I'm still willing to admit I'd prefer me arithmetic checked!!!!]
Arne notes this epoch bit in chat 3600.

The rest is just a response to Arne's note, especially as some of it don't
tally with other things other professionals _seem_ to do/say:

Arne Henden wroteth:

>        Some misconceptions seem to be propogating, so
>        I'd like to step in.
...
>        First, I will reiterate that you should not be using
>        USNO-Axx numeric "IDs". These *do not* exist in the
>        actual catalog and depend on whether you are indexing
>        into each zone with zero-relative or one-relative programs.
>        They change between versions, will not be the same
>        with USNO-A3.0 or USNO-B and just add to the identification
>        confusion. Please only use coordinates!

I actually only used these because others had already used them in other
posts [indeed, I cut and pasted them from these posts!!!!], as I wanted to
avoid the potential confusion I may cause by using 'star "north"' etc.

BUT VERY IMPORTANTLY : Arne, I've said it afore, and I'll say it again :
CDS ViZieR chucks out these verdammt USNO Axx numeric IDs!!!

Here's a cut and paste from ViZieR for the 1st 5 objects centred on 0 0 0
-0 0 0:

>   1   0.9794  23 59 57.51  +00 00 45.3  0900-20545268  359.989609
0.012589                16.7  14.8  1951.607
>    2   1.1209  23 59 55.63  -00 00 15.2  0825-20075666  359.981803
-0.004225                19.3  17.8  1951.607
>    3   1.2957  23 59 55.19  +00 00 29.0  0900-20545118  359.979959
0.008042                19.4  18.7  1951.607
>    4   1.8171  23 59 57.39  +00 01 41.8  0900-20545262  359.989137
0.028270                18.0  17.1  1951.607
>    5   1.8662  00 00 07.31  -00 00 22.4  0825-00000501    0.030478
-0.006209                16.8  15.3  1951.607
>  

The first two columns are ViZieR internal stuff to do with the query [sort
number and distance in arcmins from requested co-ords], then the USNO A2.0
data stars with RA and Dec columns and "USNO A2.0" is the heading for the
next column!!!! [eg 0825-00000501]

Nearly everybody uses these IDs.  I've read Dave Monet's words on this
matter, _don't do it_, but no bugger else seems to have [yourself excluded].

I try not to use non-standard nomenclature, but sometimes I have to give in
else it is hard to talk about the same thing with other folk!  I try hard,
at least, when I do use this route to include the prefix USNO A2.0 [which
is the only one I use], with some folk not even bothering with this.

Arne, in general I agree with yourself and Dave Monet, but that only ends
up in me being in a minority of 3 or so when it comes to talking to
variable star folk.

>        Second, UCAC is based on a Kodak 4kx4k CCD on a 0.2m telescope,
>        not a 1.0-m telescope. Pixel density is not the same as for
>        2MASS. They are both current-epoch, however.

Completely my fault, a consequence of using memory instead of re-reading
the specs!!!! I'm probably thinking 2MASS and DENIS [?????]  Note this is
Arne's only statement that isn't a "grey area".  Having said this, Arne's
USNO A2.0 point is _valid_ and not a grey area, but then again I seem to
remember the next millennium has already started a year early due to
popular [mis]use.

>        Third, UCAC also does not have numeric "IDs". These
>        again are being supplied by some access program -- I strongly
>        recommend not promulgating these non-numbers! UCAC1 is just
>        an interim release of the catalog (we have 6 updates here
>        at NOFS already, with another due this month), and misses many
>        stars that will eventually be incorporated into the catalog.

Ah, good.  I can blame USNOFS for this 'error' on my part! ;).  Here's a
cut and paste _direct_ from the UCAC1 readme.txt file!!!!!:

>- Identification: explicit star numbers are not provided.  It is
>    recommended to use the running line number over all data (index
>    files, see below) and use an 8-digit after the string "1UCAC"
>    (compliant with IAU recommendations).  Example: "1UCAC00000001"
>    would be the first star in the first zone, while "1UCAC27425433"
>    is the last star in our current catalog.  Also, the position of a
>    star can be used as identifier in any case.

So, I did use the running number as stated above.  _And_ I had to do it by
hand, not via some access program , cos all I've got is a file giving me
zonal running numbers (zone.txt), and then I decompress a zone and have to
use an ascii reader to see what line this is actually on, and then add it
to the zonal running number...

...which is tedious, and I only do it cos that's what it says I ought to!!
I'd rather not.

I'd assumed the next public release would be called UCAC2, to negate this
numbering change problem.  ie 2UCACnnnnnnnn would be the new system, and
2UCACn... != 1UCACn... for any xUCACn...

Now you tell me it ain't so!

>        Fourth, USNO-A is exclusively from POSS-I plates. These
>        are epoch 1950; there are no 1987 plates in USNO-A. POSS-I
>        plates *are* contemporaneous; the red and blue pairs were
>        taken back-to-back. You may be confusing USNO-A with the
>        PMM pixel server, which has digitized POSS-II as well as
>        many other recent surveys. Since USNO-A, 2MASS and UCAC
>        are all ICRS/J2000, the one arcsec difference between
>        USNO-A and 2MASS/UCAC is most likely just 50-year proper motion.

PLEASE, anyone who has read this far kindly note that this last bit from
vsnet-chat 3599 is negated by the following vsnet-chat 3600 posting from
Arne.  It is no big deal, but I don't want folk to negate the proper motion
point just for the sake of it, and without checking.

>Oops.
>               I forgot that USNO-A1.0 and USNO-A2.0 had different
>               crossover points between northern and southern surveys.
>               The -21 degree zone in USNO-A2.0 is from the southern
>               Schmidts, and those plates are what John Graves mentioned:
>               1976 and 1987, non-contemporaneous. The USNO-A1.0 catalog
>               used Palomar POSS-I plates for this zone, and these were
>               contemporaneous. Yet another difference to keep in mind.
>               Sorry! This Northern observer keeps neglecting his
>               southern sky studies!
>               Arne

[NB it greaves me to note a graves error in my name spelling ;) ]

FINALLY : Arne, clarification on these sort of things is more than
welcome!!!  I've read many a paper by professionals that are often even
more "nomeclaturally challenged" [to be pc] than the rest of us.  I try to
use the CDS nomenclature dictionary exclusively, unless the people I'm
talking to insist on using another nomenclature [it only leads to confusion
on their part if I don't give in]. One example of which is my constant
nagging of folk who consistently get the Stephenson Carbon star catalogues'
prefixes muddled.  Analogous to your USNO Ax and xUCACn points, Stephenson
numbering don't tally twixt cat editions!!!!

Do any folk who use USNO Ax.x numbers like to say why they started doing it?

Cheers

John

JG, UK

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