[vsnet-chat 1565] Photometric reference file update

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

     Some substantial changes and additions have been made to my large file
of faint photometric reference stars, so I thought I would let folks know
about these.
     The file, which now includes over 19,000 stars, contains equinox 2000
coordinates and BVRI photometry (as available) for stars mostly fainter than
V mag. 10.0.  The median value is V=14.0, so roughly speaking half the stars
lie between 10.0 and 14.0, while the other half are between 14.0 and about
18.5 (some stars to mag. 22).  It can be obtained from:

http://ftp.lowell.edu/pub/bas/starcats/loneos.stds   (1.3Mb)

The "version number" of this file is given by the date at the top of the list.
There is also now a growing file of bibliographic citations from which the data
were extracted:

http://ftp.lowell.edu/pub/bas/starcats/loneos.ref

     The major addition to the catalogue is that GSC numbers have now been
added for practically all stars that have them.  This should make the list more
readily useful for many people.  The GSC match-up was done by Bill Gray
(the Project Pluto "Guide" software guy), and I am grateful to have had this
done so quickly and expertly.
     One significant by-product of the GSC matching is that stars from the
Guide Star Photometric Catalogue (GSPC) now have reliable positions.  The
positions given in the source publication---which was completed before the
GSC itself---have errors of typically 2" to 20", but in several fields they are
off by 10' or 20', simply wrong.  Luckily, the GSPC charts allow the correct
positions to be recovered.
     Among added stars are a number of sequences along the southern Milky Way
by Seggewiss, Lynga, Bok, even a "secret" deep UBVRI sequence by Landolt near
eta Carinae.  I have also made a start at adding more reliable sequences in the
Clouds, but there is still a lot of work to do there.  In all cases, I have
included stars as bright as V=10.0, since it is clear that many observers will
find stars just below the limit of _reliable_ Tycho photometry to be useful for
photographic and wide-field CCD sky patrols.
     Michael Richmond (Rochester Inst. Technology), of the TASS amateur sky
survey group, has kindly produced plots of the distribution of the stars from
my list, and posted them at the TASS Web site:

http://a188-L009.rit.edu/tass/catalogs/catalogs.html#loneos
http://a188-L009.rit.edu/tass/catalogs/loneos_radec.gif

...for all-sky equal-area and rectangular RA/Dec projections.  The first URL
contains some additional details about data.  The figures show that no matter
where you're pointed in the sky there is always a set of calibration stars
within a few degrees.  Large regions near the galactic poles and "downtown
Virgo cluster" are particularly well covered.  Using these stars, one can make
local corrections to the GSC and USNO-A catalogues to place those magnitudes
closer to the standard system.
     Michael has also made a version of file with BVRI magnitudes explicit,
rather than as V mags and colors (as in my file), in a form more suitable for
use in many types of automated analysis:

http://a188-L009.rit.edu/tass/catalogs/loneos.cat

     All for now.

\Brian Skiff  (bas@lowell.edu)

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