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I/329               URAT1 Catalog                             (Zacharias+ 2015)

The first U.S. Naval Observatory Astrometric Robotic Telescope Catalog (URAT1) Zacharias N., Finch C., Subasavage J., Bredthauer G., Crockett C., Divittorio M., Furguson E., Harris F., Harris H., Henden A., Kilian C., Munn J., Rafferty T., Rhodes A., Schultheiss M., Tilleman T., Wieder G. <Astron. J., 150, 101 (2015)> =2015AJ....150..101Z =2015yCat.1329....0Z
ADC_Keywords: Surveys ; Positional data ; Proper motions Description: URAT is a follow-up project to the successful UCAC project using the same astrograph but with a much larger focal plane array and a bandpass shifted further to the red. Longer integration times and more sensitive, backside CCDs allowed for a substantial increase in limiting magnitude, resulting in about 4-fold increase in the average number of stars per square degree as compared to UCAC. Additional observations with an objective grating largely extend the dynamic range to include observations of stars as bright as about 3rd magnitude. Multiple sky overlaps per year result in a significant improvement in positional precision as compared to UCAC. A URAT1 release paper for the Astronomical Journal is in preparation. URAT1 is an observational catalog at a mean epoch between 2012.3 and 2014.6; ot covers the magnitude range 3 to 18.5 in R-band, with a positional precision of 5 to 40 mas. It covers most of the northern hemisphere and some areas down to -24.8° in declination. Acknowledging URAT1: File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file urat1.sam 294 1000 URAT1 catalog urat1doc.txt 79 2008 Description of URAT1 (readme.urat1) URAT1/v12/* 0 59 Binary files URAT1/access/* 0 59 Access URAT1/info/* 0 59 Info
See also: I/289 : UCAC2 Catalogue (Zacharias+ 2004) I/315 : UCAC3 Catalogue (Zacharias+ 2009) I/322 : UCAC4 Catalogue (Zacharias+ 2012) Byte-by-byte Description of file: urat1.sam
Bytes Format Units Label Explanations
1- 10 A10 --- URAT1 URAT1 recommended identifier (ZZZ-NNNNNN) (13) 12- 22 F11.7 deg RAdeg Right ascension on ICRS, at "Epoch" (1) 24- 34 F11.7 deg DEdeg Declination on ICRS, at "Epoch" (1) 36- 38 I3 mas sigs Position error per coordinate, from scatter (2) 40- 42 I3 mas sigm Position error per coordinate, from model (2) 44- 45 I2 --- Ns (nst) Total number of sets the star is in (3) 47- 48 I2 --- Nu (nsu) Number of sets used for mean position (3) 50- 57 F8.3 yr Epoch (epoc) Mean URAT observation epoch (1) 59- 64 F6.3 mag f.mag ?(mmag) mean URAT model fit magnitude (4) 66- 70 F5.3 mag e_f.mag ?(sigp) URAT photometry error (5) 72- 73 I2 --- Nm (nsm) Number of sets used for URAT magnitude (3) 75 I1 --- r (ref) largest reference star flag (6) 77- 79 I3 --- Nit (nit) Total number of images (observations) 81- 83 I3 --- Niu (niu) Number of images used for mean position 85- 87 I3 --- Ngt (ngt) Total number of 1st order grating observations 89- 91 I3 --- Ngu (ngu) Number of 1st order grating positions used 93- 98 F6.1 mas/yr pmRA ?(pmr) Proper motion RA*cosDec (from 2MASS) (7) 100-105 F6.1 mas/yr pmDE ?(pmd) Proper motion in Declination (7) 106-109 F4.1 mas/yr e_pm ?(pme) Proper motion error per coordinate (8) 112-113 I2 --- mf2 [1/11] Match flag URAT with 2MASS (9) 115-116 I2 --- mfa [1/11] Match flag URAT with APASS (9) 118 A1 --- G [-] "-" if there is no match with GSC2.4 (14) -------------------------------------------------------------------------------- 120-129 I10 --- 2Mkey ?(id2) unique 2MASS star identification number 131-136 F6.3 mag Jmag ?(jmag) 2MASS J-band magnitude 138-142 F5.3 mag e_Jmag ?(ejmag) Error on Jmag 144-145 A2 --- q_Jmag [0,58]? J-band quality-confusion flag (10) 147-152 F6.3 mag Hmag ?(hmag) 2MASS H-band magnitude 154-158 F5.3 mag e_Hmag ?(ehmag) Error on H-band magnitude (10) 160-161 A2 --- q_Hmag [0,58]? H-band quality-confusion flag (10) 163-168 F6.3 mag Kmag ?(kmag) 2MASS Ks-band magnitude 170-174 F5.3 mag e_Kmag ?(ekmag) Error on Ks-band magnitude (10) 176-177 A2 --- q_Kmag [0,58]? Ks-band quality-confusion flag (10) -------------------------------------------------------------------------------- 179-181 I3 --- Nn (ann) Number of APASS observation nights (12) 183-185 I3 --- No (ano) Number of APASS observations (12) 187-192 F6.3 mag Bmag ?(abm) APASS B-band magnitude (11) 194-198 F5.3 mag e_Bmag ?(ebm) Error on Bmag 200-205 F6.3 mag Vmag ?(avm) APASS V-band magnitude 207-211 F5.3 mag e_Vmag ?(evm) Error on Vmag 213-218 F6.3 mag gmag ?(agm) APASS g-band magnitude 220-224 F5.3 mag e_gmag ?(egm) Error on gmag 226-231 F6.3 mag rmag ?(arm) APASS r-band magnitude 233-237 F5.3 mag e_rmag ?(erm) Error on rmag 239-244 F6.3 mag imag ?(aim) APASS i-band magnitude 246-250 F5.3 mag e_imag ?(eim) Error on imag
Note (1): Positions are on the International Celestial Reference System (ICRS) as represented by the UCAC4 catalog. Mean observed positions are given at mean epoch of URAT observations (column "Epoch"). Thus the epoch is slightly different from star to star, but it is always in the range between 2012.311 and 2014.679. Note that the position is originally given in mas, i.e. ±3 in the last digit. Note (2): Column "sigs" gives the mean position error of the mean position as given in columns "RAdeg" and "DEdeg" as derived from the scatter of individual observations. A mean was taken over RA and Dec component errors because they are very similar for most stars. In case only a single observation was made a conservative estimate from error propagation is made. An error floor of 5 mas is added RMS to the scatter error to arrive at the value given in URAT1. Column "sigm" gives another estimate of the error of the mean position components. Here a model is used which includes image profile fit (x,y data) errors, atmospheric turbulence, and astrometric reduction error propagations. As for the scatter error, a systematic error floor of 5 mas was added RMS. The model error is likely a better estimate of the true positional errors than the scatter error, at least for small numbers of observations. Note (3): The 2 years of observing used for this catalog release was split into a total of 38 sets of data (19 each for regular survey and one grating survey). Unless very bright or very faint or variable, a source on the sky should show up in several sets (adjacent sets, 1st and 2nd year at same season...). If an object is within the about 5 to 17.5 mag range and does not show up in several sets it is suspicious and might be a variable or moving source or sometimes blended image. Note (4): This is the mean, observed magnitude in the 680-750 nm URAT bandpass, calibrated by APASS photometry. This bandpass is between R and I, thus further into the red than UCAC. Observations in non-photometric nights *are* included thus the URAT magnitudes need to be taken with caution. Unknown or unrealistic magnitudes are blanked. The faintest maybe real celestial object magnitude is about 19.0, while the URAT1 catalog should be complete to about magnitude 18.0. Note (5): The photometric error of URAT bandpass observations is derived from the scatter of individual observations. A systematic error floor of 0.01 mag has been RMS added. Unknown errors were blanked. Note (6): Each object on every individual exposure and CCD gets a reference star flag assigned during the conventional, astrometric "plate" reduction. The largest value of this flag for a given star over all its observations is carried into this URAT1 catalog flag. The meaning of the values of this flag is as follows: 0 = not a reference star 1 = o.k, both coordinates used as reference star 2 = x-coord. excluded in adjustment 3 = y-coord. excluded in adjustment 4 = x and y-coord. excluded in adjustment 5 = not selected due to astrometry flag 6 = too bright on URAT exposure (amplitude limit exceeded) 7 = no valid sigma_xy from profile fit on URAT exposure 8 = excluded by distance from URAT center (accepted field of view) 9 = excluded because outside of adopted UCAC4 magnitude range The UCAC4 was used as reference star catalog, however, only "clean" (astrometry flag) UCAC4 stars within the 8.0 to 16.0 mag were used. Thus there are some UCAC4 stars with reference star flag 5 and 9. These are identified, valid UCAC4 stars but were not used as reference stars in the URAT1 astrometric reductions. Note (7): These are strictly 2-epoch proper motions using the 2MASS point source catalog as early epoch and the URAT observational data as second epoch. A match radius of 3arcsec was used to identify common sources. With a mean epoch difference of about 14 years, the largest valid proper motion can be only about 200 mas/yr. Stars with higher proper motions were not attempted to match for this release, neither were other catalogs used to improve the proper motions. The goal here was to quickly provide the community with a useful product: accurate reference stars at current epoch. The provided preliminary proper motions allow to use the URAT1 data for a window of ± several years of its observational epoch without significant degradation of positional accuracy. Note (8): The error on a proper motion component was derived from error propagation of assumed precision of the input data. A fixed position error of 80 mas was adopted for 2MASS and the model position error of individual URAT stars was used to derive the error in proper motion. No systematic error floor was added here. Typical errors in proper motions are 5 to 8 mas/yr. Note (9): The meaning of the match flag is as follows: 1 = unique match 3 = multiple match but only 1 match with high confidence 5 = closest positional match used in case of multiple matches 7 = 2nd catalog multiple match, use closest positional match 9 = likely wrong match 11 = no match at all Thus match flags up to 3 are considered "good", 5 and 7 "maybe". Note (10): Values of 2MASS magnitudes are just copied from the 2MASS point source catalog (II/246). In case no 2MASS data are available, the magnitudes and errors are blank, and flags are 0. For each 2MASS bandpass 2 flags are combined, the cc_flg (contamination flag, 0 to 50) and the ph_qual flag (photometric quality flag, 0 to 8) with the following explanations (from the 2MASS documentation): 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. Note (11): A custom set of APASS (The AAVSO Photometric All-Sky Survey) data was kindly provided to us by Arne Henden to include the DR8 data plus single photometric observations. For a total of 71614 stars with no DR8 data the DR6 data was used. In case no APASS data are available, the magnitudes and the photometric errors are blank. Note (12): A few stars had more than 127 APASS nights or observations. These numbers were trimmed to 127 to fit into the signed I*1 variable. Note (13): the URAT1 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; 326 is actually the southmost zone), and NNNNNN the 6-digit running number in the zone. Note (14): the minus sign (originally embedded in the "Nu" column) indicates stars which were not matched with the GSC 2.4 catalog (about 1.1 million objects, priv. comm. R.Smart). Some of these are fake entries in URAT (like a minor planet at a certain epoch), others appear to be slightly offset from a real star (possible large proper motion object), and others are at the limiting magnitude thesholds. In order to pick a somewhat cleaner sample of URAT reference stars these objects could be avoided, or at least those which also do not match up with 2MASS.
Acknowledgements: It is a pleasure to thank Norbert Zacharias, who wrote most of this introduction and answered to several questions. History:
(End) Norbert Zacharias [USNO], Francois Ochsenbein [CDS], Thomas Boch [CDS] 18-Feb-2015
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

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