| The Fifth USNO CCD Astrograph Catalog |
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| The Fifth USNO CCD Astrograph Catalog |
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From the Readme of UCAC5 project files Version 2.0 170224 NZ, CF, incl. zone files description See also https://arxiv.org/abs/1702.05621 . Contact Norbert Zacharias 1) Overview, goals 2) Procedure 3) Results 4) File formats 5) Some statistics
The 1st Gaia data release provides proper motions for only about 2 million stars (TGAS subset of the Tycho-2 stars) in the mainly 6 to 11.5 magnitude range. Gaia DR2 which will contain proper motions of about a billion stars is scheduled for release in April 2018. In the meantime the astronomical community would benefit from proper motions of millions of stars fainter than the Tycho-2 limit, if a substantial improvement in precision and accuraccy could be made beyond what was available in the pre-Gaia era.
Such improvements are achieved here with 2 new products:
Please see also the upcoming paper (Zacharias, Finch, Frouard, AJ), which contains several usful figures and validation results for the UCAC5 data.
The number of matches appears low at first glance but is similar to what was shown at the Madrid ESA Gaia meeting for a match between Gaia DR1 and the PPMXL catalog, which contains a similar amount of stars as NOMAD, both based on the same large photographic sky surveys of the last century. The small difference between the Gaia system and the ICRF were neglected at this time because of the relatively large position errors of NOMAD of about 100 to 200 mas per coordinate.
A catalog was generated which contains an entry for every Gaia DR1 star. For the TGAS stars the Gaia data was copied into the new catalog. For other stars matched with NOMAD new proper motions were calculated based on the about 1970 NOMAD and 2015 Gaia epoch positions. Proper motions of the remaining not matched stars were set to zero.
The NOMAD file also contains photographic plate magnitudes and 2MASS photometry. These data were propagated into the NOMAD-Gaia output file as well. A Gaia G-mag vs. 2MASS J color index for example is output on the UCAC-TGAS file (see below).
No changes in the systematic error correction model as function of magnitude were made. These were obtained from earlier dedicated reductions with 2MASS stars to allow complete coverage of the UCAC magnitude range. The TGAS data only reaches to about magnitude 11.5 and is thus not suitable for a re-evaluation of the systematic errors as a function of magnitude (the UCAC limiting magnitude is about 16.5). Nevertheless, residuals of the TGAS solutions were plotted as a function of magnitude and systematic errors in the accessible magnitude range are small (order 5 mas or less) for the global averages of all data. Local sub-sets of the data show somewhat larger systematic errors in the order of up to 10 mas, as expected from previous UCAC4 results.
A new catalog of UCAC mean positions from these reductions with TGAS was constructed containing over 180 million entries covering all-sky. These positions have mean epochs around 1998-2000 in the south, and around 2001 to 2003 in the north. Formal position errors are about 8 mas around magnitude 11, 20 mas at magnitude 14, and 60 mas at magnitude 16 (see Journal paper).
For several millions of stars up to about magnitude 14 the errors on these new proper motions are on the same level as the TGAS proper motions (1 to 2 mas/yr, see below). This set of UCAC - Gaia matched stars with new positions and proper motions is called "UCAC5".
Formal errors on the new proper motions were calculated by root-square-sum of a) formal position error of UCAC, b) formal position error of TGAS (both at their respective mean epochs), and c) a systematic error contribution of 10 mas at the UCAC epoch data. This RSS value was then divided by the epoch difference to arrive at the proper motion errors given in the UCAC5 data files.
file name RECL n.records description ---------------------------------------------------------------------- u5tgas.dat 133 F 2054491 TGAS + UCAC5 PM, diff.PM u5cat.dat 40 B 107758513 UCAC5 PM (Gaia + UCAC) Dec sorted z001..900 52 B 107758513 UCAC5 Dec zone files, sorted by RA u5index.asc 1296000 ASCII table of index data for zone files u5index.unf 5184000 B 2 same as binary data u5gnom.dat 28 B 540130390 other stars: NOMAD + Gaia PM ----------------------------------------------------------------------The files u5cat.dat and the zone files contain the same stars with the same data, except that on the zone files the Gaia 2015 epoch positions and errors were added for convenience (ready to be used as reference star catalog).
Although contained in the main UCAC5 catalog, a separate file was output listing only the UCAC5-TGAS stars. Because of its small size it is a plain ASCII text file with fixed columns (see below) also containing the original TGAS proper motions and the differences between the UCAC5 and TGAS proper motions.
Of course there is some correlation between the 2 sets of proper motions because the new UCAC reductions used TGAS as reference star catalog. However, only 6 (linear) parameters need to be solved for in each of the UCAC exposure reductions and on average about 50 TGAS stars were used for that with 2 coordinates each. Furthermore, the UCAC results are based on typically 4 individual exposures with different telescope pointings. This large overdetermination in those least-squares reductions lead to a largely independent observation of the TGAS star positions while k
eeping the UCAC results strictly on the Gaia reference frame. The following histograms were obtained from the UCAC-TGAS file (for description of columns, see below). The bin size is given on the 2nd row of these histograms, while the 1st column gives the bin number. The rest of the table gives the number of stars per bin with respect to the data item of a particular column. The first and last bin (+-40) contain also stars beyond that bin.
col 3 4 5 6 7 8 9 10 bins 0.50 0.10 10.00 10.00 10.00 10.00 1.00 1.00 -40 0 7205 180 302 181 299 178 1667 -39 0 0 17 23 16 19 22 224 -38 0 0 16 24 14 22 17 248 -37 0 1 11 19 13 20 18 271 -36 0 1 27 36 22 36 39 281 -35 0 0 17 39 23 37 36 287 -34 0 1 18 37 18 41 20 322 -33 0 0 34 42 37 37 32 340 -32 0 0 35 47 32 41 41 375 -31 0 2 35 61 35 61 48 399 -30 0 0 43 57 43 59 48 404 -29 0 1 56 63 54 61 63 476 -28 0 0 51 77 51 75 64 455 -27 0 1 74 105 72 100 74 458 -26 0 0 75 92 80 90 82 482 -25 0 1 91 112 89 114 82 494 -24 0 0 108 144 104 138 90 534 -23 0 1 112 161 120 154 98 513 -22 0 0 138 211 132 198 113 524 -21 0 1 156 226 155 217 126 464 -20 0 2 165 265 155 272 153 517 -19 0 3 215 304 230 305 151 497 -18 0 2 253 375 248 359 175 558 -17 0 3 306 480 303 463 204 592 -16 0 0 359 561 349 566 236 648 -15 0 2 459 674 470 669 284 709 -14 0 2 604 849 606 821 326 773 -13 0 2 731 1021 731 1013 422 882 -12 0 2 978 1356 979 1308 533 946 -11 0 1 1268 1732 1223 1682 704 1001 -10 0 1 1628 2401 1651 2289 966 1212 -9 0 6 2297 3258 2291 3124 1363 1589 -8 0 5 3215 4471 3177 4346 2045 2101 -7 0 2 4689 6617 4649 6242 3144 2906 -6 0 9 6977 10262 7010 9771 5209 4247 -5 0 4 11342 15962 11377 15148 9807 7041 -4 0 17 19367 27259 19271 26317 19532 13630 -3 0 61 36575 49334 36585 47977 43912 31628 -2 0 218 78712 103386 79215 101948 109370 89223 -1 0 819 228717 269007 232773 271642 280984 275747 0 0 10958 1368621 1367485 1361344 1369721 1093433 1200110 1 0 18507 146435 108655 148709 110855 287759 266353 2 0 30678 59828 37368 60395 37376 108701 80301 3 0 43499 29295 16473 29346 16224 41650 28033 4 0 57762 16644 8599 16583 8260 18350 11719 5 0 75284 9894 4799 9938 4581 8731 5922 6 0 106078 6381 2915 6324 2817 4854 3375 7 0 178874 4168 1789 4226 1744 2911 2011 8 1 258543 3032 1222 3006 1148 1805 1426 9 57 244880 2068 896 2082 867 1195 1037 10 280 160039 1516 647 1492 621 845 784 11 1061 86469 1208 437 1206 435 587 612 12 3914 64282 890 332 886 318 454 489 13 7602 89391 688 236 700 241 324 451 14 13267 123862 567 206 563 227 277 391 15 23291 120531 498 140 499 137 228 340 16 38961 91810 386 130 377 135 183 307 17 64829 67395 295 114 307 112 155 281 18 105470 51517 257 80 252 82 132 257 19 165937 38997 221 82 225 76 117 234 20 249813 30301 177 65 185 65 79 244 21 324964 23149 158 45 150 44 77 206 22 418591 17747 141 47 143 45 54 212 23 401725 13864 119 31 114 35 63 182 24 200782 10949 103 29 103 29 67 164 25 31986 8406 76 29 76 27 44 147 26 1672 6465 68 27 67 23 48 129 27 178 4860 57 13 58 15 50 143 28 52 3699 54 21 56 22 45 132 29 34 2645 39 12 36 16 46 119 30 13 1923 36 14 40 11 34 124 31 9 1313 35 11 30 12 32 123 32 1 823 30 7 33 8 36 144 33 1 328 34 4 32 4 24 141 34 0 110 35 9 36 9 29 143 35 0 60 23 7 24 6 21 119 36 0 29 20 8 20 6 10 137 37 0 18 20 6 19 3 18 120 38 0 15 24 6 28 8 19 105 39 0 9 21 3 16 5 14 122 40 0 46 178 40 181 40 179 1437 col 11 12 13 14 bins 0.10 0.10 0.10 0.10 0 0 0 76960 82501 1 0 0 13647 9156 2 0 0 10766 10434 3 0 0 36991 63046 4 0 0 71194 126986 5 0 0 104172 175529 6 2805 2805 127204 214072 7 77900 79029 143305 218864 8 260493 263601 144521 197908 9 379555 384762 138639 164546 10 389890 393335 126617 125406 11 320180 320746 115043 99207 12 200119 194090 101302 78431 13 120603 117170 88455 64172 14 61428 59285 76703 54194 15 31859 31115 68243 46826 16 37886 37292 60296 40167 17 27519 27557 54719 34362 18 34650 35051 49538 29586 19 23336 22893 44474 24934 20 19544 19225 39224 21356 21 15851 15576 35700 17638 22 14879 15070 31178 15118 23 9636 9511 28154 12936 24 6730 6732 25206 11439 25 5426 5326 22841 9603 26 4171 4247 20521 8702 27 2315 2325 18411 7705 28 2285 2214 16793 6886 29 1614 1693 15340 6250 30 836 842 13933 5636 31 1124 1043 12988 4969 32 702 793 11879 4579 33 294 306 10985 4183 34 156 158 9870 3946 35 129 119 9133 3556 36 96 106 7785 3201 37 71 65 6309 2952 38 77 86 5643 2810 39 51 45 4919 2611 40 281 278 54890 38088The distribution of the new UCAC-Gaia proper motions are very similar to that of the TGAS data. The formal errors of the UCAC-Gaia proper motions (columns 11, 12) peak at 1.0 mas/yr, comparable to the accuracy of the TGAS proper motions. Fewer stars have errors of 1.5 mas/yr or larger in UCAC-Gaia proper motions than in TGAS.
a) u5tgas.dat (TGAS stars, formatted file) total number of records = 2054491 column number, min, max, average, number of stars used for average: 1 0.000 360.000 187.166 2054491 RA [degree] 2 -89.890 89.832 -3.220 2054491 Dec [degree] 3 4.395 16.571 10.815 2054491 Gaia magnitude 4 -9.000 7.871 1.134 2047284 G-J color index 5 -1274.500 1134.800 -1.757 2044105 U5 PM RAc [mas/yr] 6 -2101.100 802.800 -4.806 2045127 U5 PM Dec [mas/yr] 7 -1271.000 1138.000 -1.740 2044088 TGAS PM RAc [mas/yr] 8 -2092.400 822.900 -4.680 2045320 TGAS PM Dec [mas/yr] 9 -178.000 79.900 -0.009 2048083 PM diff. RAc U-G [mas/yr] 10 -85.900 92.600 -0.048 2032327 PM diff. Dec U-G [mas/yr] 11 0.700 70.200 1.215 2054436 error U5 PM RAc [mas/yr] 12 0.700 70.200 1.212 2054436 error U5 PM Dec [mas/yr] 13 0.010 18.340 1.375 2044466 error TGAS PM RAc [mas/yr] 14 0.010 18.850 1.069 2045546 error TGAS PM Dec [mas/yr] 15 7627862074752 6917521537218608640 Gaia source ID number range 16 1.000 52.000 5.598 2054491 numb. all images 17 0.000 47.000 4.945 2054491 numb. used images b) u5cat.dats (main catalog file) total number of records = 107758513 column number, min, max, average, number of stars used for average: 1 34359896320 6917528649684202496 Gaia ID number range 2 1.000 3.000 2.064 107758513 flg 3 0.000 59.000 2.769 107758513 nu 4 1.121 7.381 3.311 107758513 epu 5 0.000 360.000 209.151 107758513 RA [degree] 6 -89.984 89.975 -10.144 107758513 Dec [degree] 7 -2867.000 2552.300 -2.263 107708547 PM RAc [mas/yr] 8 -2210.700 1647.600 -3.189 107710634 PM Dec [mas/yr] 9 0.700 103.100 4.083 96852222 error PM RAc [mas/yr] 10 0.700 99.600 4.108 98241877 error PM Dec [mas/yr] 11 3.240 23.554 15.156 107758513 Gaia mag 12 3.872 20.000 15.549 107758513 UCAC mag 13 0.000 30.000 15.763 98803442 R mag 14 -0.676 30.000 13.906 98803441 J mag 15 -1.739 30.000 13.445 98803434 H mag 16 -2.099 30.000 13.324 98803426 K mag c) Gaia-NOMAD file (upon request to Norbert Zaharias) total number of records = 503640468 column number, min, max, average, number of stars used for average: 1 65408 6917528993283204480 Gaia source ID number range 2 0.00 360.00 212.14 503640468 RA [degree] 3 -89.99 89.90 -10.15 503640468 Dec [degree] 4 5.24 28.61 18.53 503640468 Gaia magnitude 5 4.32 30.00 18.63 503640468 R mag 6 1.77 30.00 23.34 503640468 J mag 7 -3271.50 3247.40 -1.67 502676536 PM RAc [mas/yr] 8 -3082.10 3258.80 -4.62 502545795 PM Dec [mas/yr] 9 0.80 32.77 3.33 485856173 error PM RAc [mas/yr] 10 0.81 32.77 3.28 485561998 error PM Dec [mas/yr] 11 60.10 96.99 80.32 503640468 epoch RA [year-1900] 12 60.10 96.99 80.32 503640468 epoch Dec [year-1900] 13 9.00 553726830.00 480549.62 503589212 NOMAD flag ======== end of UCAC5 readme file