The Third U.S. Naval Observatory CCD Astrograph Catalog Definitions

UCAC3 Overview

UCAC3 is a compiled, all-sky star catalog covering mainly the 8 to 16 magnitude range in a single bandpass between V and R. Positional errors are about 15 to 20 mas for stars in the 10 to 14 mag range. It is supplemented by proper motions and SuperCosmos and 2MASS photometric data, as well as various flags.

The UCAC3 documentation can be found here. Additional details are available in the release paper Zacharias et al. 2010, AJ, 139, 2184. Note: in order to place uncertainties immediately following the corresponding quantities, some columns have been reordered relative to what is described in these documents.

UCAC3 Column Descriptions

Gator serves the UCAC3 (42 columns, 100,766,420 data rows). The column descriptions can be found below.

Name Intype Units Description
ra double degree RA_J2000 (J2000 R.A. of source)
dec double degree DEC_J2000 (J2000 Dec. of source)
ran int4 mas right ascension at epoch J2000.0 (International Coordinate Reference System)
spdn int4 mas south pole distance epoch J2000.0 (ICRS)
To convert to Declination, subtract 324000000 mas.
sigra int2 mas error in RA (*cos Dec) at central epoch
sigdc int2 mas error in Dec at central epoch
im1 double mag UCAC fit model magnitude
Unknown or unrealistic results are set to mag = 18
im2 double mag UCAC aperture magnitude
Unknown or unrealistic results are set to mag = 18
sigmag double mag UCAC error on magnitude
A value of -0.001 is "unknown".
Errors exceeding 0.9 mag were set to 0.9 mag.
objt int2 object type:
-2 = warning: object could be from possible streak
-1 = warning: object is near overexposed star
0 = good star
1 = good star (data copied from another entry)
2 = warning: contains at least 1 overexposed image
3 = warning: all images are overexposed or "bad"
dsf int2 double star flag:
0 = single star
1 = primary of pair with unreal secondary = single
2 = forced separation, on same frame
3 = blended image, some CCD frames show single star, some double
4 = forced separation, 2 objects on same frame number
5 = primary component of real double
6 = secondary component of real double
7 = other "odd" case
cepra int2 0.01 yr central epoch for mean RA, minus 1900
cepdc int2 0.01 yr central epoch for mean Dec, minus 1900
na1 int2 total # of CCD images of this star
nu1 int2 # of CCD images used for this star
Zero means that all images have some "problem"; in this case
the mean position is derived by an unweighted mean of all (na1) images.
us1 int2 # catalogs (epochs) used for proper motions
cn1 int2 total # catalogs (epochs) initial match
pmrac int2 0.1 mas/yr proper motion in RA*cos(Dec)
sigpmr int4 0.1 mas/yr error of pmrac (-10 is null)
pmdc int2 0.1 mas/yr proper motion in Dec
sigpmd int2 0.1 mas/yr error of pmdc (-10 is null)
id2m int2 2MASS pts_key identification number
jmag double mag 2MASS J magnitude
e2mphoj int2 mag 2MASS J magnitude uncertainty
hmag double mag 2MASS H magnitude
e2mphoh int2 mag 2MASS H magnitude uncertainty
kmag double mag 2MASS K_s magnitude
e2mphok int2 mag 2MASS K magnitude uncertainty
icqflg char 2MASS cc_flg*10 + ph_qual flag, for each 2MASS band in order.
0x = no contamination
1x = possible latent
2x = photometric confusion
3x = diffraction spike
4x = electronic stripe
5x = bandmerge confusion
 x0 = no ph_qual flag
x1 = no valid brightness est.
x2 = upper limit
x3 = unreliable error
x4 = poor profile fit
x5 = ph_qual A valid measurement
x6 = ph_qual B valid measurement
x7 = ph_qual C valid measurement
x8 = ph_qual D valid measurement
smB double mag SuperCosmos B magnitude
smR2 double mag SuperCosmos R magnitude from the second epoch Schmidt plates (R2)
smI double mag SuperCosmos I magnitude
clbl char SC star/galaxy classif./quality flag: blend*10 + meanclass
0x = no blending
1x = possible blending detected
 x1 = galaxy
x2 = star
x3 = unclassifiable
x4 = noise
qfB int2 SuperCosmos quality flag B magnitude:
-1 = qual blank in SuperCOSMOS, no flag given
0 = qual zero in SuperCOSMOS, no problems detected
1 = qual < 128 in SuperCOSMOS, reliable image
2 = qual < 65535 in SuperCOSMOS, problems detected
3 = qual ≥ 65535 in SuperCOSMOS, spurious detection
qfR2 int2 SuperCosmos quality flag R2 magnitude
Definitions same as qfB
qfI int2 SuperCosmos quality flag I magnitude
Definitions same as qfB
catflg char Multiple catalog match flag: Each digit refers to one of ten major catalogs
HipTychoAC2000 AGK2B AGK2H ZA BY Lick SC SPM
digit 123 4 5 6 7 8 9 10
The value for each digit has the following meaning:
0 = star not matched with this catalog
1 = unique match, not involving a double star
2 = closest match, not involving a double, likely o.k.
3 = unique match, and involving a double star
4 = closest match, and involving a double, likely o.k.
5 = maybe o.k. smallest sep. match in both directions
6 = same as 5, but involving a double star
g1 int2 Yale SPM objt type(g-flag):
0 = no info
1 = matched with 2MASS extended source list
2 = LEDA galaxy
3 = known QSO
c1 int2 Yale SPM input cat(c-flag), indicating which input catalog has been
used to identify stars for pipeline processing:
1 = Hipparcos
2 = Tycho2
3 = UCAC2
4 = 2MASS psc
5 = 2MASS xsc (extended sources, largely (but not all!) galaxies)
6 = LEDA (confirmed galaxies, Paturel et al. 2005)
7 = QSO (Veron-Cetty & Veron 2006)
leda int2 arcsec LEDA galaxy match flag:
Value is either 0 (no match) or the log of the apparent I-band diameter
(arcsec) from the LEDA catalog.
A size value less than 1 has been rounded up to 1.
x2m int2 arcsec 2MASS extend.source flag:
Value is either 0 (no match) or the length of the semi-major axis (arcsec)
of the fiducial ellipse at the K-band from the 2MASS XSC.
Sizes larger than 127 arcsec have x2m = 127.
rn int4 Star identification (MPOS) number
Values greater than 140,000,000 indicate high proper motion stars.