Access to Astronomical Catalogues

← Click to display the menu
I/322A              UCAC4 Catalogue                 (Zacharias+, 2012)

The fourth U.S. Naval Observatory CCD Astrograph Catalog (UCAC4) Zacharias N., Finch C.T., Girard T.M., Henden A., Bartlett J.L., Monet D.G., Zacharias M.I. <Astron. J. 145, 44 (2013)> =2012yCat.1322....0Z =2013AJ....145...44Z
ADC_Keywords: Surveys ; Positional data ; Proper motions Description: UCAC4 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. Proper motions have been derived for most of the about 113 million stars utilizing about 140 other star catalogs with significant epoch difference to the UCAC CCD observations. These data are supplemented by 2MASS photometric data for about 110 million stars and 5-band (B,V,g,r,i) photometry from the APASS (AAVSO Photometric All-Sky Survey) for over 50 million stars. UCAC4 also contains error estimates and various flags. All bright stars not observed with the astrograph have been added to UCAC4 from a set of Hipparcos and Tycho-2 stars. Thus UCAC4 should be complete from the brightest stars to about R=16, with the source of data indicated in flags. UCAC4 also provides a link to the original Hipparcos star number with additional data such as parallax found on a separate data file included in this release. The proper motions of bright stars are based on about 140 catalogs, including Hipparcos and Tycho, as well as all catalogs used for the Tycho-2 proper motion construction. Proper motions of faint stars are based on re-reductions of early epoch SPM data (-90 to about -20 deg Dec) and NPM (PMM scans of early epoch blue plates) for the remainder of the sky. These early epoch SPM data have also been combined with late epoch SPM data to arrive at proper motions partly independent from UCAC4 (Girard et al. 2011AJ....142...15G, Cat. I/320). The NPM data used in UCAC4 are not published. No Schmidt plate data are used in UCAC4. The unpublished plate measure data obtained by StarScan from the AGK2, the Hamburg Zone Astrograph, the USNO Black Birch Astrograph, and the Lick Astrograph have contributed to considerable improvement in proper motions for stars mainly in the 10 to 14 mag range (down to the UCAC limit for Lick data); however, these data do not cover all sky. Recources permitting, USNO plans to release the individual CCD observations (RA,Dec at epoch of each CCD observations) in the future. Please contact if you are interested in obtaining this set of about 50 GB data. We will likely request that interested users provide an external disk drive for the data release. Acknowledging UCAC4: The paper (Zacharias et al., 2013, AJ, 145, 44) should be cited whenever UCAC4 data is utilized. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file out.sam 294 1000 Sample UCAC4 output (out of 113780093 stars) ucac4doc.txt 79 2008 Description of UCAC4 (readme_u4)
See also: : UCAC home page I/289 : UCAC2 Catalogue (Zacharias+ 2004) I/315 : UCAC3 Catalogue (Zacharias+ 2009) I/247 : The AC2000 Catalogue (Urban+ 1997) I/259 : The Tycho-2 Catalogue (Hog+ 2000) I/264 : Sixth Catalogue of Fundamental Stars (FK6) (Wielen+ 2000) I/277 : SPM Catalog 2.0 (Platais+ 1998) I/317 : The PPMXL Catalog (Roeser+ 2010) II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) VII/242 : LEDA galaxies with DENIS measurements catalog (Paturel+, 2005) VII/248 : Quasars and Active Galactic Nuclei (12th Ed.) (Veron+ 2006) Byte-by-byte Description of file (# headlines): out.sam
Bytes Format Units Label Explanations
1- 10 A10 --- UCAC4 UCAC4 recommended identifier (ZZZ-NNNNNN) (1) 12- 22 F11.7 deg RAdeg Mean right ascension (ICRS), Ep=J2000 (2) 23- 33 F11.7 deg DEdeg Mean declination (ICRS), Ep=J2000 (2) 35- 37 I3 mas e_RAdeg Mean error of RAdeg at mean epoch 39- 41 I3 mas e_DEdeg Mean error of DEdeg at mean epoch 43- 46 I4 mas ePos Total mean error on position at Ep=J2000 (3) 48- 54 F7.2 yr EpRA Central epoch for mean RA 56- 62 F7.2 yr EpDE Central epoch for mean Declination 64- 69 F6.3 mag f.mag ? UCAC fit model magnitude (579-642nm) (4) 71- 76 F6.3 mag a.mag ? UCAC aperture magnitude (579-642nm) (4) 78- 81 F4.2 mag e_a.mag ? Mean error on f.mag and a.mag (5) 85 I1 --- of [0/9] UCAC4 object classification flag (6) 87- 88 I2 --- db [0/36] UCAC4 double star flag (7) 90- 92 I3 --- Na [0/71] Number of UCAC observations for the star 94- 96 I3 --- Nu [0/70] Number of used UCAC observations (8) 98-100 I3 --- Nc [1/38] Number of catalog positions used for pm 102-109 F8.1 mas/yr pmRA ? Proper motion in RA(*cos(Dec)) (9) 111-118 F8.1 mas/yr pmDE ? Proper motion in Dec (9) 120-123 F4.1 mas/yr e_pmRA ? Mean error on pmRA (9) 125-128 F4.1 mas/yr e_pmDE ? Mean error on pmDE (9) -------------------------------------------------------------------------------- 130-138 I9 --- MPOS1 [1/182895114] Unique star ID number (10) 140-149 A10 --- UCAC2 UCAC2 (Cat. I/289) designation (ZZZ-NNNNNN) 151-162 A12 --- Tycho-2 Tycho-2 (Cat. I/259) designation (FFFF-NNNNN-N) -------------------------------------------------------------------------------- 164-173 I10 --- 2Mkey ? 2MASS (Cat. II/246) Unique source identifier 175-180 F6.3 mag Jmag ? 2MASS J magnitude (1.2um) 182-185 F4.2 mag e_Jmag ? Mean error (rounded to 0.01mag) 186 A1 --- --- [:] 187-188 I02 --- q_Jmag [0,58]? J-band quality-confusion flag (11) 190-195 F6.3 mag Hmag ? 2MASS H magnitude (1.6um) 197-200 F4.2 mag e_Hmag ? Mean error (rounded to 0.01mag) 201 A1 --- --- [:] 202-203 I02 --- q_Hmag [0,58]? H-band quality-confusion flag (11) 205-210 F6.3 mag Kmag ? 2MASS Ks magnitude (2.2um) 212-215 F4.2 mag e_Kmag ? Mean error (rounded to 0.01mag) 216 A1 --- --- [:] 217-218 I02 --- q_Kmag [0,58]? K-band quality-confusion flag (11) -------------------------------------------------------------------------------- 220-225 F6.3 mag Bmag ? B magnitude from APASS (12) 226 A1 --- --- [:] 227 A1 --- f_Bmag [.-] Actual or S/N estimated error (12) 228-229 I02 cmag e_Bmag ? Estimated error on Bmag (12) 231-236 F6.3 mag Vmag ? V magnitude from APASS (12) 237 A1 --- --- [:] 238 A1 --- f_Vmag [.-] Actual or S/N estimated error (12) 239-240 I02 cmag e_Vmag ? Estimated error on Vmag (12) 242-247 F6.3 mag gmag ? g magnitude from APASS (12) 248 A1 --- --- [:] 249 A1 --- f_gmag [.-] Actual or S/N estimated error (12) 250-251 I02 cmag e_gmag ? Estimated error on gmag (12) 253-258 F6.3 mag rmag ? r magnitude from APASS (12) 259 A1 --- --- [:] 260 A1 --- f_rmag [.-] Actual or S/N estimated error (12) 261-262 I02 cmag e_rmag ? Estimated error on rmag (12) 264-269 F6.3 mag imag ? i magnitude from APASS (12) 270 A1 --- --- [:] 271 A1 --- f_imag [.-] Actual or S/N estimated error (12) 272-273 I02 cmag e_imag ? Estimated error on imag (12) -------------------------------------------------------------------------------- 275 I1 --- g [0,3] g-flag from SPM (13) 276 I1 --- c [0,7] c-flag from SPM (14) 277 A1 --- --- [.] 278 I1 --- H [0/9] Hipparcos/Tycho flag (15) 279 I1 --- A [0/8] AC2000 flag (16) 280 I1 --- b [0/8] AGK2 Bonn match flag (16) 281 I1 --- h [0/8] AGK2 Hamburg match flag (16) 282 I1 --- Z [0/8] Zone astrographic match flag (16) 283 I1 --- B [0/8] Black Birch match flag (16) 284 I1 --- L [0/8] Lick Astrographic match flag (16) 285 I1 --- N [0/8] NPM Lick match flag (16) 286 I1 --- S [0/8] SPM Lick match flag (16) 289-290 I2 [6arcsec] LEDA LEDA I-band galaxy match (17) 293-294 I2 arcsec 2MX 2MASX K-band match (18)
Note (1): the UCAC4 number is the recommended identification of UCAC4 stars. It made as "ZZZ-NNNNNNN", where zzz is the zone number (between 1 and 900 from South pole to North pole, each zone being 0.2° wide), and nnnnnn the 6-digit running number in the zone. Note (2): 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 proper motions. The observational UCAC position is but one of several going into these values and is not given in the UCAC4; thus the original UCAC observation cannot be recovered from these data. Note (3): taking into account the propagation of the proper motion error between the mean epoch and J2000. Note (4): systematic errors are expected to be below 0.1mag. The aperture photometry (a.mag) is considered more robust, particularly for "odd" cases, while the model fit magnitude is expected to be more accurate for "well behaved" stars. Note (5): 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 0.9mag the error was set to 0.9mag Note (6): the object type flag is used to identify possible problems with a star and has the following meaning: 0 = good, clean star, no known problem 1 = near overexposed star 2 = possible streak object 3 = high proper motion (HPM) star 4 = actually use external HPM data instead of UCAC4 observed data (accuracy of positions varies between catalogs) 5 = poor proper motion solution, report only CCD epoch position 6 = substitute poor astrometric results by FK6/Hip/Tycho-2 data 7 = added supplement star (no CCD data) from FK6/Hip/Tycho-2 data, and 2 stars added from high proper motion surveys 8 = high proper motion solution in UCAC4, star not matched with PPMXL 9 = high proper motion solution in UCAC4, discrepant motion to PPMXL Note (7): The double star flag is used to indicate the type/quality of double star fit. It is a combination of 2 flags, dsf+dst: * dsf = double star flag, represents the overall classification: 0 = single star 10 = component #1 of "good" double star 20 = component #2 of "good" double star 30 = blended image * dst = double star type, derived from pixel data image profile fits (largest value of all images used for this star): 0 = no double star, not sufficient #pixels or elongation to even call double star fit subroutine 1 = elongated image but no more than 1 peak detected 2 = 2 separate peaks detected -> try double star fit 3 = secondary peak found on each side of primary 4 = case 1 after successful double fit (small separation, blended image) 5 = case 2 after successful double fit (most likely real double) 6 = case 3 after successful double fit (brighter secondary picked) Note (8): 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 (9): For astrometric data copied from the FK6, Hipparcos and Tycho-2 catalogs a mean error in positions was adopted depending on input catalog and the brightness of the star rather than giving the individual star's error quoted in those catalogs. Note (10): This unique star identification number is between 200001 and 321640 for Hipparcos stars, and between 1 and 9430 for non-Hipparcos stars supplemented to the UCAC4 catalog (no CCD observation). For all other stars this unique star identification number is the internal mean-position-file (MPOS) number + 1million. Note, there are several thousand cases where different UCAC4 stars link to the same Hipparcos star number due to resolved binary stars with each component being a separate star entry in UCAC4. Note (11): For each 2MASS bandpass a combined flag was created (cc_flg + ph_qual) consisting of the contamination flag (0 to 50) and the photometric quality flag (0 to 8). 0 = cc_flg 2MASS '0', no artifacts or contamination 10 = cc_flg 2MASS 'p', source may be contaminated by a latent image 20 = cc_flg 2MASS 'c', photometric confusion 30 = cc_flg 2MASS 'd', diffraction spike confusion 40 = cc_flg 2MASS 's', electronic stripe 50 = 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, snr>10 AND cmsig<0.10857 6 = ph_qual 2MASS 'B', valid measurement, snr> 7 AND cmsig<0.15510 7 = ph_qual 2MASS 'C', valid measurement, snr> 5 AND cmsig<0.21714 8 = ph_qual 2MASS 'D', valid measurement, no snr OR cmsig req. For example the value 05 is decoded to be cc_flg=0, and ph_qual=5, meaning no artifacts or contamination and 2MASS qual flag = "A". Note (12): Data are from the AAVSO Photometric all-sky survey (APASS) DR6 plus single observation stars kindly provided by A.Henden. For bright stars the Bmag and Vmag columns contain the Hipparcos/Tycho Bt and Vt mags respectively, whenever there is no APASS B or V available and valid Bt or Vt mags were found. The errors flagged with "-" are formal errors estimated from the S/N, while the "normal" errors (flagged with ".") are from the official release data error estimates (at least 2 observations per 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 (2MASX 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 (Cat. I/311) 2 = Tycho2 (Cat. I/259) 3 = UCAC2 (Cat. I/289) 4 = 2MASS psc (Cat. II/246) 5 = 2MASS xsc (extended sources, Cat. VII/233; largely galaxies) 6 = LEDA (confirmed galaxies, Paturel et al. 2005) 7 = QSO (Veron-Cetty & Veron 2006, Cat. VII/248) Note (15): The FK6-Hipparcos-Tycho-source-flag has the following meaning: 0 = not a Hipparcos or Tycho star 1 = Hipparcos 1997 version main catalog (Cat I/239) 2 = Hipparcos double star annex 3 = Tycho-2 (Cat. I/259) 4 = Tycho annex 1 5 = Tycho annex 2 6 = FK6 position and proper motion (instead of Hipparcos data) 7 = Hippparcos 2007 solution position and proper motion (Cat. I/311) 8 = FK6, only PM substitution (not in UCAC4 data) 9 = Hipparcos 2007, only proper motion substituted (Cat. I/311) Note (16): The catflg match flag is provided for major catalogs used in the computation of the proper motions. Each match is analyzed for multiple matches of entries of the 1st catalog to 2nd catalog entries, and the other way around. Matches are also classified by separation and difference in magnitude to arrive at a confidence level group. The flag has the following meaning: 0 = star not matched with this catalog 1 = unique-unique match, not involving a double star 2 = unique-unique match, but involving a flagged double star 3 = multiple match but unique in high confidence level group, no double 4 = as 3, but involving a flagged double star 5 = closest match, not involving a double, likely o.k. 6 = closest match, but involving a flagged double star 7 = maybe o.k. smallest separation match in both directions, no double 8 = as 7, but involving a flagged double star Note (17): value is either 0 (no match) or contains the log of the apparent total diameter (in 0.1arcmin) 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 (18): 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.
Acknowledgements: It is a pleasure to thank Norbert Zacharias, who wrote most of this introduction and answered to many questions. History: * 01-Aug-2012: Original version * 30-Jan-2013 (version 'A'): Fix 3416 high proper motion stars The fix concerns 3416 stars in 416 binary zone files between 6 and 449. All affected stars have object type flag = 4, i.e. stars observed with the astrograph and mean position and proper motion taken from external catalogs. Only the proper motion columns are affected by this bug, all other data items of those stars remain as they are in the UCAC4. The Python script file "" patches the original zone files.
(End) Norbert Zacharias [USNO], Francois Ochsenbein [CDS] 24-Jul-2012
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

catalogue service