[vsnet-chat 3615] USNO Ax.0 "identifications"

[crawl@zoom.co.uk]

As a general problem I have with regards to nomenclatural conventions,
often highlighted by data from various people I am in contact with, and
specifically with respect to objects contained in USNO Ax.0 sources, I have
been in contact with the prime author of that catalogue to request some
clarification.

It should first be noted that the lack of any explicit "name" or
"designation" in the USNO Ax.0 catalogues is primarily a space saving
exercise, for obvious reasons.  It should also be noted that it is more
usual for such astrometric catalogues to be used to derive the astrometric
position of an object via measurements and analyses with respect to several
of the stars in the catalogue, and including statistical information
regarding residuals, errors and what have you.  The actual practice of
identifying a variable with a specific USNO Ax.0 object rather than using
USNO Ax.0 objects to derive a calculated position is probably peculiar to
the variable star community.  This is probably best highlighted by the
problems caused in such cross identification work when a variable has
significant proper motion.

On checking with the prime author, it seems there is no valid naming
convention for USNO Ax.0.

On the other hand, and in _my_ interpretation, the lack of any valid naming
convention is the primary reason that people do not feel that the naming
conventions they have adopted are invalid.

I can only suggest therefore that if people in the variable star community
feel the need to utilise an identifier for a USNO Ax.0 object that they either

i) include an acknowledgement to the software &/or server used to derive
this identifier

or

ii) include the full reference to the online readme file or published
article from which they themselves have derived the rules by which they
have generated this identification.

Also note that Dave Monet, the primary author of USNO Ax.0, explicitly
states in the USNO A2.0 documentation that the appropriate USNO Ax.0
catalogue _must_ be stated as part of any identifier, for the stellar
content of 1.0 and 2.0 is not the same!

Arne Henden rightly pointed out that problems will be caused by people
using different variations on the naming theme.  As none of these
variations are _strictly_ invalid, and as people will most likely _not_
refrain from using them, their full provenance should be included to avoid
confusion at future times.

It would at least be useful if people included something like [CDS] or
[ESO] or similar at the end of the USNO object details [ie on the same
line] to indicate if the data was gleaned from either of those servers, for
example.

Despite Arne's admonition on the use of such names, experience has shown me
that everybody uses them, and a few cases have probably already gotten into
the odd IBVS.


Recent cases of newly noted variables in crowded fields have shown that
USNO B will be useful in variable star progenitor identification due to the
proper motion data it will contain.

Ironically, and importantly, Arne's admonition will be strictly relevant
when USNO B is eventually released.  I had, with some naivety, requested
that stronger guidelines be considered re naming when that catalogue was
released.

The hindsight obvious response was that in the USNO B instance this would
not be feasible.  USNO B will contain proper motion information based on
multi-epoch plates, and as such it will not be possible to generate one
unique plate identification for each object.

No doubt this will not stop people trying...

Cheers

John


[ PS Oh, and incidently, the number of angels on a pinhead is equal to the
pinhead's surface area divided by the angels' average cross-sectional area,
especially when there is a 'z' in the month ;-) ]

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