This all-sky catalog, described in Monet et al. (2003), consists of positions, proper motions, magnitudes, and other measured quantities for 1,045,175,762 objects. (This number was verified by Dave Monet in March 2008 using the original USNO-B1.0 files at the USNO in Flagstaff. It should be noted that this number differs slightly from the value reported in Monet et al. 2003.) The data were derived from digitizing scans of almost 7,500 photographic plates taken from various sky surveys during the interval from 1949 to 2002. The originating plate material includes five complete coverages of the northern sky and four of the southern sky.
To be included in the catalog, an object must have been detected on two different surveys because isolated, single-survey detections are unreliable. For the earlier USNO-A catalog (which was essentially a two-color, one-epoch catalog), this meant that the object must have had detectable fluxes on both the red and blue plates, and this led to the exclusion of many faint objects with non-neutral colors. Also, the larger epoch difference in the southern survey coverage meant that objects with larger proper motions tended to be excluded. USNO-B1.0 attempts to fix both of these problems. An object detected in the same band at two epochs will be included in USNO-B1.0, as will objects that have significant proper motions, although it is still the case that objects with large motions and extreme colors may be omitted. The selection algorithm requires that spatially coincident detections must be made on any two of the surveys for an object to be classified as real and be included in the catalog.
The catalog is expected to be complete down to V=21. Estimated positional accuracies are 0.2 arcsec, photographic magnitude accuracies are 0.3 mag, and the accuracy for distinguishing stars from non-stellar objects is 85%.
The following table contains brief descriptions of the parameters provided for each object in the USNO-B1.0 catalog. The columns are:
|USNO_B1||%12s||---||no||The USNO-B1 identifier is a 12 character string of the form ZZZZ-NNNNNNN consisting of the four-digit zone number (ranging from 0000 at the South Pole to 1799 at the North Pole), followed by a dash ('-'), and terminated with a 7 digit sequence number starting at 0000001 and ending at the number of objects in the zone. The USNO-B1.0 objects are arranged in zones of 0.1 deg in declination, with objects ordered by Right Ascension in each zone.|
|Tycho2||%12s||---||yes||Designation in the Tycho-2 Catalog.|
|ra, dec||%10.6f||deg||no||Right Ascension and Declination of the source. Coordinates are given in equinox J2000 at epoch 2000.0. Proper motion was applied to compute these epoch-2000.0 RA and Dec values. Note that large uncertainties in the proper motions mean that RA and Dec are less accurate than the mean errors e_ra and e_dec which apply to the position at the mean epoch.|
|e_ra||%3i||mas||no||One-sigma error on RA*cos(Dec) at mean epoch.|
|e_dec||%3i||mas||no||One-sigma error on Dec at mean epoch.|
|epoch||%6.1f||yr||no||Mean epoch of observation.|
|pm_ra||%7i||mas/yr||yes||Proper motion in RA, measured relative to the YS4.0 Catalog. See Monet et al. (2003) for details.|
|pm_dec||%7i||mas/yr||yes||Proper motion in Dec, measured relative to the YS4.0 Catalog. See Monet et al. (2003) for details.|
|pm_prob||%1i||0.1||yes||Total proper motion probability, in units of tenths. For Tycho-2 stars, the total proper motion probability pm_prob is not given.|
|e_pm_ra||%3i||mas/yr||yes||Mean one-sigma error on pm_ra.|
|e_pm_dec||%3i||mas/yr||yes||Mean one-sigma error on pm_dec.|
|e_fit_ra||%1i||100mas||yes||Total one-sigma error in RA at the predicted epoch-2000 position. This value includes the measured positional and proper motion uncertainties.|
|e_fit_dec||%1i||100mas||yes||Total one-sigma error in Dec at the predicted epoch-2000 position. This value includes the measured positional and proper motion uncertainties.|
|ndet||%1i||---||yes||Number of detections. For Tycho-2 stars ndet is set to 0. For other stars, valid values of ndet are 2, 3, 4, or 5.|
|flags||%3s||---||yes||A three-character flag that encodes the following information:
First character: If 'M', this means the motion is confirmed in another catalog
In any of the three positions, the '.' character denotes the absence of a flag. Examples of possible flags are 'M.., '...', 'M.Y', and 'MsY'.
|b1_mag, r1_mag, b2_mag, r2_mag, i_mag||%5.2f||mag||yes||Measured magnitude. The prefix refers to the band:
b1 = first blue observation
|b1_cal, r1_cal, b2_cal, r2_cal, i_cal||%1i||---||yes||Source of photometric calibration. This is represented by a number between
0 and 9:
0 = bright photometric standard on plate
|b1_survey, r1_survey, b2_survey, r2_survey, i_survey||%1i||---||yes||Survey number:
0 = POSS-I O
|b1_field, r1_field, b2_field, r2_field, i_field||%3i||---||yes||Field number in survey.|
|b1_class, r1_class, b2_class, r2_class, i_class||%2i||---||yes||Star/galaxy classification, which is a measure of the similarity of the
point-spread function to a stellar profile. This is an integer with a sliding range
from 0 to 11:
0 means quite dissimilar (i.e. a non-stellar object)
For example, values between 0 and 3 indicate objects likely to be non-stellar, and values from 8 to 11 indicate objects that are likely stellar.
|b1_xi, r1_xi, b2_xi, r2_xi, i_xi||%6.2f||asec||yes||Distance of the photo-center from the object's mean position. Calculations for positions and motions are done in the tangent plane using the standard coordinates xi and eta with the mean position taken as the tangent point.|
|b1_eta, r1_eta, b2_eta, r2_eta, i_eta||%6.2f||asec||yes||Distance of the photo-center from the object's mean position. Calculations for positions and motions are done in the tangent plane using the standard coordinates xi and eta with the mean position taken as the tangent point.|
[Last Updated: 2008 July 18, by J. Davy Kirkpatrick]