[vsnet 983] USNO A1.0 on-line

[bas@lowell.Lowell.Edu (Brian Skiff)]

     As some of you may know, the U. S. Naval Observatory in Flagstaff has
produced a colossal star catalogue called "A1.0". The catalogue contains almost
500,000,000 detections, including stars, galaxies, etc.  The data will not in
general be available except for scientific use, and cannot be used in
commercial applications.  The general Web site describing the catalogue can
be found at:

http://www.usno.navy.mil/pmm

     The site includes links to two third-party search utilities, one from
Doug Mink at SAO/CfA and the other to the Lowell Observatory site.
     Since Lowell Observatory folks will making use of the catalogue for
various purposes, Bruce Koehn of the Lowell staff has made a Web page with a
form for searching small areas of the A1.0 catalogue.  The URL is:

http://asteroid.lowell.edu

This is the top page for various asteroid-related products.  Included is Ted
Bowell's 32,000+ asteroid orbital element database, asteroid search routines,
and other goodies.  There is also a link to "refnet", which is the star
catalogue search form.
     The search form includes access to the full A1.0, the "SA1.0" faint
astrometric subset (for use with small CCD fields, for instance), and also
the complete PPM catalogue (480,000 brighter stars).  The search inputs
include RA/Dec, search area, magnitude, and so on; the output can be sorted
by RA, radius from search center, etc.
     The output itself includes the A1.0 position (equinox 2000 at epoch of
the POSS-I blue plate used for the scans, i.e. about 1950-1955), the red and
blue magnitude, the radius from the search center, and the position angle.  At
the moment the p.a. runs the wrong direction (i.e. sweeps around from north to
_west_), but this will get fixed eventually.  The magnitudes have been adjusted
only very approximately, and possess zero-point errors of up to a couple of
magnitudes.  The colors inferred from the red/blue magnitudes can likewise be
completely non-physical---I've found stars with "blue minus red" colors of -3
to -5, which cannot occur in the real world except in blue jeans and lapis
lazuli.  I'm finding the blue magnitudes are closer to reality than the red
ones.
     The form defaults to a search area 10 arcminutes square.  Unles you are
well outside the Milky Way, this results in very long star lists.  I would
advise changing this to at most 1'-3' (60 or 180 arcseconds on the form).
     Like other catalogues built from scans of photographs, there are gaps
around bright stars (often including the bright star itself), bright galaxies,
bright globular clusters, etc., where the plates were simply black and the
star-finding algorithm couldn't operate.  By "bright", I mean stars brighter
than mag. 10-12, and galaxies with total V magnitudes brighter than mag. 12
or so---stuff that's completely saturated on the Schmidt plates.
     Have fun with it!

\Brian Skiff  (bas@lowell.edu)

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