| The Third USNO CCD Astrograph Catalog
Data Format
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|
num item fmt unit explanation remark
------------------------------------------------------------------------
1 ra I*4 mas right ascension at epoch J2000.0 (ICRS) (1)
2 spd I*4 mas south pole distance epoch J2000.0 (ICRS) (1)
3 im1 I*2 millimag UCAC fit model magnitude (2)
4 im2 I*2 millimag UCAC aperture magnitude (2)
5 sigmag I*2 millimag UCAC error on magnitude (larger of sc.mod)(3)
6 objt I*1 object type (4)
7 dsf I*1 double star flag (5)
16
8 sigra I*2 mas s.e. at central epoch in RA (*cos Dec)
9 sigdc I*2 mas s.e. at central epoch in Dec
10 na1 I*1 total # of CCD images of this star
11 nu1 I*1 # of CCD images used for this star (6)
12 us1 I*1 # catalogs (epochs) used for proper motions
13 cn1 I*1 total numb. catalogs (epochs) initial match
8
14 cepra I*2 0.01 yr central epoch for mean RA, minus 1900
15 cepdc I*2 0.01 yr central epoch for mean Dec,minus 1900
16 pmrac I*4 0.1 mas/yr proper motion in RA*cos(Dec)
17 pmdc I*4 0.1 mas/yr proper motion in Dec
18 sigpmr I*2 0.1 mas/yr s.e. of pmRA * cos Dec
19 sigpmd I*2 0.1 mas/yr s.e. of pmDec
16
20 id2m I*4 2MASS pts_key star identifier
21 jmag I*2 millimag 2MASS J magnitude
22 hmag I*2 millimag 2MASS H magnitude
23 kmag I*2 millimag 2MASS K_s magnitude
24 icqflg I*1 * 3 2MASS cc_flg*10 + phot.qual.flag (7)
25 e2mpho I*1 * 3 2MASS error photom. (1/100 mag) (8)
16
26 smB I*2 millimag SuperCosmos Bmag
27 smR2 I*2 millimag SC R2mag (9)
28 smI I*2 millimag SC Imag
29 clbl I*1 SC star/galaxy classif./quality flag (10)
30 qfB I*1 SC quality flag Bmag (11)
31 qfR2 I*1 SC quality flag R2mag (11)
32 qfI I*1 SC quality flag Imag (11)
10
33 catflg I*1 * 10 mmf flag for 10 major catalogs matched (12)
34 g1 I*1 Yale SPM object type (g-flag) (13)
35 c1 I*1 Yale SPM input cat. (c-flag) (14)
36 leda I*1 LEDA galaxy match flag (15)
37 x2m I*1 2MASS extend.source flag (16)
38 rn I*4 MPOS star number; identifies HPM stars (17)
18
------------------------------------------------------------------------
84 = total number of bytes per star record
Note (1): Positions are on the International Celestial Reference
System (ICRS) as represented by the Hipparcos / Tycho-2 catalogs.
The epoch for the positions of all stars is J2000.0; the weighted
mean catalog position was updated using the provided proper
motions. The observational UCAC position is but one of several
going into these values and is not given in the UCAC3, thus the
original UCAC observation cannot be recovered from these data.
The declination is given in south pole distance (spd) and can be
converted back to a true declination by subtracting 324000000 mas.
Note (2): Unknown, or unrealistic photometric results are set to
magnitude = 18 (18000 mmag entry in catalog). Systematic errors
are expected to be below 0.1 mag for im1, im2 photometric results
obtained from the UCAC CCD pixel data. The aperture photometry
is considered more robust, particularly for "odd" cases, while the
model fit magnitude is expected to be more accurate for "well
behaved"
stars.
Note (3): A value of -1 for error in magnitude means "unknown".
For many stars a photometric error based on the scatter from
individual observations of that star on different CCD frames
could be obtained. A model error was also attempted to be
assigned, based on the S/N ratio. The error quoted here is
the larger of the 2. If that error exceeds 0.9 mag the error
was set to 0.9 mag (900 mmag entry in catalog data).
Note (4): The object type flag is used to identify possible problems
with a star and has the following meaning:
-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"
Note (5): The dsf flag is a double star flag used to indicate the
type/quality of double star fit with the following meaning:
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
Note (6): A zero for the number of used images indicates that all
images
have some "problem" (such as overexposure). In that case an
unweighted
mean over all available images (na) is taken to derive the mean
position, while normally a weighted mean was calculated based on
the "good" images, excluding possible problem images (nu <= na).
Note (7): For each 2MASS bandpass a combined flag was created
(cc_flg*10 + ph_qual) consisting of the contamination flag (0 to 5)
and the photometric quality flag (0 to 8).
0 = cc_flg 2MASS 0, no artifacts or contamination
1 = cc_flg 2MASS p, source may be contaminated by a latent image
2 = cc_flg 2MASS c, photometric confusion
3 = cc_flg 2MASS d, diffraction spike confusion
4 = cc_flg 2MASS s, electronic stripe
5 = cc_flg 2MASS b, bandmerge confusion
0 = no ph_qual flag
1 = ph_qual 2MASS X, no valid brightness estimate
2 = ph_qual 2MASS U, upper limit on magnitude
3 = ph_qual 2MASS F, no reliable estimate of the photometric error
4 = ph_qual 2MASS E, goodness-of-fit quality of profile-fit poor
5 = ph_qual 2MASS A, valid measurement, [jhk]snr>10 AND
[jhk]cmsig<0.10857
6 = ph_qual 2MASS B, valid measurement, [jhk]snr> 7 AND
[jhk]cmsig<0.15510
7 = ph_qual 2MASS C, valid measurement, [jhk]snr> 5 AND
[jhk]cmsig<0.21714
8 = ph_qual 2MASS D, valid measurement, no [jhk]snr OR [jhk]cmsig
req.
For example icqflg = 05 is decoded to be cc_flg=0, and ph_qual=5,
meaning
no artifacts or contamination from cc_flg and 2MASS qual flag = "A"
.
Note (8): The photometric errors from 2MASS were rounded by 1 digit
here to fit into fewer bytes (1/100 mag instead of millimag).
Note (9): The R magnitude from the second epoch Schmidt plates (R2) is
used for UCAC3, as provided in the SuperCosmos source catalog.
Note (10): clbl is a combination of the SuperCOSMOS "meanclass" and
modified "blend" flag (meanclass + 10*blend) originally for each
magnitude (B, R1, R2, I). The flag provided here is the maximum
value over all bands for each of the 2 flags. The SuperCOSMOS mean
class flag is an estimate of image class based on unit-weighted mean
of individual classes from (B, R1, R2, I). The SuperCOSMOS modified
blend flag indicates if blending is detected.
The "meanclass" has the following meaning from SuperCOSMOS:
1 = galaxy
2 = star
3 = unclassifiable
4 = noise
The modified "blend" flag has the following meaning:
0 = no blending
1 = possible blending detected
Note (11): This is a modified quality flag from the "qualB", "qualR2",
and "qualI" quality flag from SuperCOSMOS, which gives an indication
of the quality of the image from the three bands (B, R2, I). The
modified quality flag qfB, qfR2, and qfI have the following meaning:
-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
Note (12): The catflg provides reference to 10 major catalogs used
in the computation of the proper motions and catalog matching.
Each of the 10 numbers range from 0 to 6 and are the "mmf"
(multiple match flag) with respect to each of the 10 following
catalogs:
Hip, Tycho, AC2000, AGK2B, AGK2H, ZA, BY, Lick, SC, SPM
catflg 1 2 3 4 5 6 7 8 9 10
The value for each byte, the mmf flag, 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
Note (13): The g-flag from the Yale San Juan first epoch Southern
Proper Motion data (YSJ1, SPM) has the following meaning:
0 = no info
1 = matched with 2MASS extended source list
2 = LEDA galaxy
3 = known QSO
Note (14): The c-flag from the Yale San Juan first epoch Southern
Proper Motion data (YSJ1, SPM) indicates 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)
Note (15): This flag is either 0 (no match) or contains the log of
the apparent total diameter for I-band (object size) information
copied from the LEDA catalog (galaxies). A size value of less
than 1 has been rounded up to 1.
Note (16): This flag is either 0 (no match) or contains the length of
the semi-major axis of the fiducial ellipse at the K-band
(object size) information copied from the 2MASS extended source
catalog. If the size is larger than 127, the flag was set to 127.
Note (17): MPOS running star numbers over 140 million indicate high
proper motion stars which were identified in UCAC pixel data from
matches with known HPM stars. The position given for those HPM
stars is the unweighted mean of the CCD observations and the
proper motion is copied from the literature catalog.
The following table gives the total range of values present these data.
# explanation unit minimum maximum
----------------------------------------------------------------------
1 right ascension epoch J2000.0 (ICRS) [mas] 2 1295999990
2 south pole distance epoch J2000.0 (ICRS) [mas] 57990 647908484
3 UCAC fit model magnitude [mmag] 2329 18000
4 UCAC aperture magnitude [mmag] 2797 18000
5 error on magnitude (larger of sc.model) [mmag] -1 900
6 object type -2 3
7 double star flag 0 7
8 s.e. at central epoch in RA (*cos Dec) [mas] 5 500
9 s.e. at central epoch in Dec [mas] 5 500
10 total numb. of CCD images per star 1 70
11 number of CCD images used per star 0 68
12 numb. catalogs (epochs) used for proper motion 1 31
13 total numb. of catalogs (epochs) initial match 0 113
14 central epoch - 1900 for mean RA [1/100 yr] -477 10438
15 central epoch - 1900 for mean Dec [1/100 yr] -938 10438
16 proper motion in RA*cos(Dec) [0.1 mas/yr] -37060 67670
17 proper motion in Dec [0.1 mas/yr] -58130 102770
18 s.e. of pmRA * cos Dec [0.1 mas/yr] -10 500
19 s.e. of pmDE [0.1 mas/yr] -10 500
20 2MASS pts_key star identifier 0 1340037129
21 2MASS J magnitude [mmag] -2652 30000
22 2MASS H magnitude [mmag] -3732 30000
23 2MASS K_s magnitude [mmag] -4227 30000
24 2MASS cc_flg*10 + phot.qual.flag J band 0 58
25 2MASS cc_flg*10 + phot.qual.flag H band 0 58
26 2MASS cc_flg*10 + phot.qual.flag K band 0 58
27 2MASS error photom. J band [1/100 mag] 0 127
28 2MASS error photom. H band [1/100 mag] 0 127
29 2MASS error photom. K band [1/100 mag] 0 127
30 SC Bmag [mmag] 0 30000
31 SC R2mag [mmag] 0 30000
32 SC Imag [mmag] 0 30000
33 SC star/galaxy classif./quality flag 0 14
34 SC quality flag Bmag -1 2
35 SC quality flag R2mag 0 2
36 SC quality flag Imag -1 2
37 mmf flag Hipparcos catalog 0 1
38 mmf flag Tycho-2 catalog 0 1
39 mmf flag AC2000 catalog 0 1
40 mmf flag AGK Bonn catalog 0 6
41 mmf flag AGK Hamburg catalog 0 6
42 mmf flag ZA catalog 0 6
43 mmf flag BY catalog 0 6
44 mmf flag Lick catalog 0 6
45 mmf flag SuperCosmos catalog 0 6
46 mmf flag SPM catalog 0 6
47 Yale SPM object type (g-flag) 0 3
48 Yale SPM input cat. (c-flag) 0 7
49 LEDA galaxy match flag (size info) 0 118
50 2MASS extend.source flag (size info) 0 127
51 MPOS star number 3 140051297