[vsnet-chat 5510] USNO-B1.0 announced

[Brian Skiff <Brian.Skiff@lowell.edu>]

     Some folks may have an interest in the upcoming USNO-B1.0 star catalogue.
This was described this afternoon (13 Sep) in a presentation by Dave Monet
at USNO-Flagstaff.  The catalogue contains just over a billion (1e10^9) stars,
about twice as many as its predecessor, USNO-A2.0.  (This is roughly 1 percent
of all the stars in the Galaxy.)  Most detections are from the well-known
series of five northern and four southern Schmidt photographic surveys in three
colors.  Some additional astrograph plate series were also scanned.  At the
bright end, the catalogue is salted with Tycho-2.
     Any object detected on any two or more plates was accepted, which will
remove various problems that appeared in A2.0 for faint red/blue stars (and
quasars etc).  There will be a crude star/galaxy separator (actually only
star/non-star) that is claimed to be about 90 percent correct, but which is
not fully analyzed.  Monet suggested that things larger than 30"-40" will be
broken up into various pieces by the blob-finder, so large galaxies will be
represented by large numbers of entries for various bits and pieces.  (This is
already the case for USNO-A2.0, so no real change here.)
     Astrometric errors of 0".15 are claimed, presumably at some mean epoch of
the plates used for any particular entry.  It should be possible to verify this
using UCAC, the Sloan calibration fields, and the ICRF galaxies directly.
Proper motions will have errors of something like 4mas/year.  "Blobs" which
moved less than 2".5 in the 40-year span of the longest-epoch baseline
(i.e. < 0".06 per year) are assumed to have zero motion and will have 0 in the
proper-motion data columns.  The public product will show positions at epoch
and equinox J2000 having a close tie to the Hipparcos-based ICRS.
     Photometry is based largely on the Guide Star Photometric Catalogue
version 2, which will probably mean a modest improvement over A2.0, but large
systematics may be present plate-by-plate (this remains to be tested).
The magnitudes will be in the native systems of the plate-series, not on
standard systems like Johnson-Cousins BVRI.
     Monet sees this catalogue as transitional to B1.1, which he suggested
could be completed in another year if things go smoothly.  This will cross-
match the final 2MASS catalogue (which also must be delivered in the coming
month or two), for which there is a 99 percent correlation in USNO-B, but with
better astrometry and of course fairly reliable photometry in the near-IR.
Delivery depends on funding and close cooperation of USNO and the 2MASS groups,
with the latter corporate marriage spoken of in terms of "if".
     Delivery.  100Gb discs will be sent to a few selected parties such as
the data centers.  USNO-Flagstaff will serve images and plotted charts, but
will not provide the catalogue in bulk.  (The scanned images have in fact been 
available for some time at:  http://vsnet.nofs.navy.mil/data/FchPix/cfra.html)
Access to star-lists will be through data-center facilties like the Strasbourg
VizieR service.  There are no plans for general bulk distribution, so no
personal copies.  If they really FedEx a hard drive copy to Strasbourg on
Monday, as Monet said was the plan, it could be that mere mortals can access
the data via VizieR sometime in October.

\Brian

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