The fourth U.S. Naval Observatory CCD Astrograph Catalog (UCAC4) Table of contents 1) Introduction a) Overview b) Differences between various versions of UCAC and how to get the data 2) Details about observations and reductions a) Observations and instrumentation b) Reductions of UCAC observations c) Data used to derive proper motions d) Computation of proper motions e) High proper motion (HPM) stars f) Photometric data 3) Properties of the catalog and important notes for the user a) Sky coverage b) Completeness c) Reference frame d) Magnitudes e) Additional photometry f) Non-stellar data g) Provided utility software h) UCAC reference material i) Arrangement of the data files j) Star identification numbers (name) k) Pitfalls for programmers / access code development 4) Files contained on the DVD 5) Data formats a) Main catalog zone files b) Min/max and check sums c) Other files 6) Description of utility software 7) Acknowledgments 8) References ====================================================================== 1) Introduction --------------- 1a) Overview ------------ This is the "readme" file of the fourth U.S. Naval Observatory CCD Astrograph Catalog, UCAC4. This data release is available free of charge on a double sided DVD or through astronomical data centers. 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. 2011). 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 nz@usno.navy.mil 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. 1b) Differences between various versions of UCAC and how to get the data ------------------------------------------------------------------------ UCAC1 = initial results covering small sky area in the south (obsolete) UCAC2 = -90 to about +50 deg Dec, 48 mill.stars, restricted to good astrometry sources, systematic astrometric error corrections performed differently than for UCAC4 (mostly obsolete by now) UCAC3 = first all-sky catalog, new pixel reductions, more elaborate systematic error corrections, push for faint limit, not as clean as UCAC2 data, several bugs affecting ~ 1 % of stars (obsolete) UCAC4 = improved version of UCAC3 = final release UCAC3 features a number of major differences with respect to UCAC2: - complete sky coverage - re-reduction of the pixel data with better modeling - double stars are resolved to the limit of the data - significantly improved photometry from CCD data - slightly deeper limiting magnitude with larger number of stars/area - reduced systematic errors of CCD observations - the addition of several new catalogs for improved proper motions - photometry in the B, R, and I bands from the SuperCosmos project - minor planet observations have been sorted out - identification of more high proper motion stars - match with 2MASS extended sources and LEDA galaxies UCAC4 is largely based on UCAC3 (same pixel data reductions), however, has a number of critical improvements over UCAC3: - bug fixes (e.g. missing stars, multiple entries, mag.eq. corrections) - use NPM data to derive proper motions of faint stars north of -20 Dec - final tweak of systematic error corrections brings it closer to UCAC2 - photometry in the B, V, g, r and i bands from APASS for 50 mill.stars - use APASS photometry to calibrate ("flatten") instrumental mags - removal of photometric bias as function of CCD x-coordinate - add brightest stars from FK6, Hipparcos and Tycho-2 catalogs - link to Hipparcos star numbers and inclusion of Hipparcos 2007 release data like parallaxes - cross reference to Tycho-2 star numbers In August 2011 a pre-release UCAC4-beta catalog was constructed and distributed to several colleagues worldwide. The UCAC team appreciates the very helpful feedback provided by these reviewers. Unfortunately due to the deployment of the URAT (Zacharias & Gaume 2010) instrument, completion of the UCAC was delayed further. A journal paper (Zacharias et al. 2012) describing the UCAC4 release is in preparation. The UCAC4 release paper should be cited whenever UCAC data are utilized. In July 2012 the UCAC4 data are sent to CDS and it is expected that the UCAC4 catalog will become on-line shortly. The UCAC4 double-sided DVD automatically will be sent to all addresses on our distribution list (people who received or requested UCAC2 or UCAC3) as fast as our resources allow. If you are not on that list or did not receive the DVD say by October 2012, please send a short e-mail request to brenda.hicks@navy.mil, put "UCAC4" in the subject line and your complete postal mailing address in the body of the message (text format). The UCAC4 comes free of charge. Technical questions may be addressed to nz@usno.navy.mil (Norbert Zacharias) or finch@usno.navy.mil (Charlie Finch). The latest update on astrometry related projects at USNO can be found at: www.usno.navy.mil/usno/astrometry . 2) Details about observations and reductions -------------------------------------------- 2a) Observations and Instrumentation ------------------------------------ The UCAC is an observational program, using the U.S. Naval Observatory Twin Astrograph and a 4k by 4k CCD camera, covering just over one square degree per frame with a scale of 0.9"/pixel. The red-corrected, 20 cm aperture, 5-element lens of the astrograph provides a 9 degree diameter field of view (designed for photographic plates), thus only a fraction is utilized with our CCD camera, centered on the optical axis. The same lens in a new tube assembly is now used with a 476 million pixel LN2 cooled camera for the URAT program (Zacharias 2004, Zacharias & Gaume 2010). The 4k CCD is a thick, Kodak device with 9 micrometer square pixels. The camera, made by Spectral Instruments, is Peltier cooled to -18 C. The raw data are severely affected by a low charge transfer efficiency (CTE) of our otherwise cosmetically excellent CCD chip. To mitigate this problem, a relatively warm operating temperature is used, causing a significant dark current. Observations started in January 1998 at Cerro Tololo Interamerican Observatory (CTIO) in Chile, where the entire southern sky and about half of the northern sky were observed. In October 2001 the instrument was moved to the Naval Observatory Flagstaff Station (NOFS) in Arizona where it completed the northern sky in 2004. A 2-fold, center-in-corner overlap pattern was adopted on a 0.5 degree grid, starting at the South Celestial Pole. Each field was observed with both a long (100 to 150 sec) and a short (20 to 30 sec) exposure. Extensive quality control routines led to the rejection of over 15% of the frames taken. All raw (pixel) data were saved and archived. Observations were made in a single bandpass (579-642 nm), thus the UCAC magnitudes are between Johnson V and R. No attempt has been made to obtain high quality, photometric data from the CCD observations. In fact, observations were made during nights with thin cirrus clouds. The telescope was actively guided with an ST-4 autoguider mounted behind the second, visually-corrected lens of the twin-astrograph. Operation was automated using a PC and a single board computer. An HP-Unix workstation was used for on-line reductions to obtain quality control statistics in near real-time. 2b) Reductions of UCAC Observations ----------------------------------- The UCAC4 positions of the CCD observations are based on the Tycho-2 reference stars (Hoeg et al. 2000), similar to the UCAC2 catalog (Zacharias et al. 2004). However, the 2MASS was utilized to probe for systematic errors in the CCD data, particularly magnitude equations and coma-like errors caused by the poor CTE of the detector (Finch, Zacharias & Wycoff 2010). Image centering is based on a modified Lorentz profile model which matches the observed PSF better than a Gaussian function (Zacharias 2010). For UCAC4 the pixel reduction results of UCAC3 was adopted with the only change being the identification and elimination of close multiple images on the same CCD frame. Pixel processing included double star fits and real aperture photometry. "Flip" observations (telescope on West and East side of pier for the same calibration fields) were utilized to fix the overall magnitude equations. Saturated images of stars were propagated through the pipeline into the output catalog. Thus similar to UCAC3, UCAC4 contains many more bright stars than UCAC2. However positional results are not as reliable as for unsaturated images and the user is urged to pay attention to flags and the meaning of various data columns. To improve this situation, a new feature was introduced with UCAC4: For stars brighter than UCAC model or aperture magnitude 8.5 and if no "good" image from UCAC CCD is available or the object is flagged as blended image or the position difference to Tycho-2 is larger than 50 mas in either coordinate, the FK6/Hipparcos/Tycho-2 astrometric data are used instead of the UCAC observational data. Furthermore, UCAC4 was supplemented by FK6/Hipparcos/Tycho-2 data for all bright stars not observed with the UCAC astrograph. The source of data is indicated by a flag in UCAC4. Nevertheless the purpose of those supplement stars is to make the user aware of these bright stars. No claim is made to have the best astrometric and photometric data available for those stars, or even have the identification right in all cases in UCAC4. Users of bright stars ought to look at a variety of catalogs to compare all information available. As before, some positions (can happen to stars of all magnitudes) are based on a center-of-mass centroiding when the least-squares fit did not succeed. Those observations are identified by number of used images (nu) equal to 0. The positions of those stars should be used with caution. 2c) Data used to derive Proper Motions -------------------------------------- A master list of exactly 181,895,143 mean positions from CCD data was matched against the various other catalogs. This number is larger than before due to a lower threshold used to accept individual images from CCD pixel data reductions. Proper motions of bright stars (R ~8 to ~12.5) were derived using a combination of ground-based photographic and transit circle catalogs, and included satellite observations from the Hipparcos and Tycho-2 catalogs. In addition, the U.S. Naval Observatory measured about 5000 astrograph plates on the StarScan machine to derive about 9 million positions for stars mainly in the 10 to 14 magnitude range, including the complete set of AGK2 (Bonn and Hamburg zones, +90 to -2.5 deg Dec), as well as about 30 % of the sky covered by the USNO Black Birch (south) and Hamburg Zone astrograph (north) programs. For the faint stars (~12.5 to ~16.5), data from the first epoch plates of the Yale Southern Proper Motions (SPM, van Altena et al. 1999) are utilized. These plates were measured on the Precision Measuring Machine (PMM) at USNO Flagstaff Station by D. Monet. A complete re-reduction of the data was performed in a joint USNO - Yale University effort utilizing the StarScan pipeline for the pixel reductions and the Yale software to obtain RA,Dec coordinates (Girard et al. 2011). The SPM data used for UCAC4 are based on the early epoch (about 1970) blue and visual plates covering the about -90 to -20 deg declination sky area. For the rest of the sky an unpublished star catalog (Girard, private comm.) based on NPM 1st epoch (about 1950) blue plates was used. These plates were also measured on the PMM and processed with the StarScan and Yale Univ. pipelines. Only for the SPM data original pixel data of plate scans were available. The NPM data shows larger systematic errors than the SPM data. However, the epoch difference to UCAC is larger for NPM than for SPM resulting in about an equal amount of estimated, remaining systematic errors of a few mas/yr for UCAC4 proper motions based on those data. When deriving UCAC4 proper motions from all individual epoch positions, estimates of systematic errors for each catalog entered the weights. The number of stars in UCAC4 which are also in major other catalogs used for the proper motions are as follows: numb.stars catalog 120487 Hipparcos (including bright supplement stars) 2506683 Tycho-2 (including bright supplement stars) 4373790 AC2000 279570 AGK2 Bonn 982815 AGK2 Hamb 4682287 Zone Astrograph 3492601 Black Birch Astrograpph 1104138 Lick astrograph selected fields 68887550 NPM Lck1 57355612 SPM YSJ1 2d) Computation of Proper Motions --------------------------------- The computation of proper motions is performed similarly to the procedure used for the UCAC2 and Tycho-2 catalogs. All input catalogs were reduced to the ICRF utilizing Hipparcos data or some denser, interim catalog that follows the system of Hipparcos. Standard errors for each position are estimated. These error estimates and RMS added, estimated systematic errors are used as weights to compute a mean position and proper motion by a weighted, least-squares adjustment procedure. Estimates of errors for UCAC4 positions and proper motions are provided. Note, while calculating proper motions, no attempt was made to correct data for parallaxes. This will lead to slightly inferior results for few stars with high parallax if it involves observations from largely different parallax factors. Errors in proper motions of the bright stars (to R ~12) run from about 1 to 3 mas/yr benefited by the large epoch spans involved. For the fainter stars using SPM and NPM data, typical errors are 2 to 6 mas/yr. Contrary to UCAC2, and similar to UCAC3, not all stars in UCAC4 have proper motions. Stars observed by the astrograph made it into the UCAC4 release catalog if any one of the following applies: - at least 2 matching positions from different CCD frames were obtained, - star was matched with a 2MASS entry, - proper motions could be obtained in combination with any other early epoch catalog. The "plots" folder of the UCAC4 distribution DVD contains all-sky plots with color coded proper motions for the RA*cosDec and Dec component, respectively. Mean proper motions for stars in 0.5 by 0.5 deg boxes are shown after cutting the low/high 15% of proper motions in each box. For more details please see also the next section and the upcoming UCAC4 journal paper, as well as the published UCAC2 and UCAC3 journal papers (also found on the UCAC4 distribution DVD). 2e) High proper motion (HPM) stars ---------------------------------- Note 1: this includes also stars with not so large a proper motion if they are present in the below mentioned external surveys and catalogs aiming at discovering high proper motion stars. Note 2: automatic processing of high proper motion stars is prone to mismatches with early epoch data and blended images cause issues. Likely there will be some false data in UCAC4 for hight proper motion astrometry. In particular, we do not claim completeness of UCAC4 data with respect to high proper motion stars. Most stars with a proper motion of about 200 mas/yr or smaller should be included in UCAC4, as well as a hand-picked sample of top high proper motion stars. However, coverage of the range in between could be significantly incomplete. Stars with high proper motions were handled specifically. First a catalog of 1.8 million stars was constructed from published proper motions. In the North the LSPM-North Catalog (Lepine & Shara 2005) of 61977 new and previously known high proper motion stars having proper motions greater than 0.15"/yr was used. In the South many smaller surveys along with the Revised NLTT Catalog (Salim & Gould 2003) were used, which produced 17730 unique high proper motion stars greater than 0.15"/yr. In both the North and South a supplement list of proper motion stars greater than ~0.15"/yr from the Tycho-2 and Hipparcos catalogs were used to fill in any gaps. In chronological order, the smaller southern surveys used include: (1) 7 papers covering various portions of the southern sky by Wroblewski and collaborators (Wroblewski & Torres 1989, 1991, 1994, 1996, 1997; Wroblewski & Costa 1999, 2001), (2) UK Schmidt Telescope survey plates of 40 survey fields by Scholz and collaborators (Scholz et al. 2000), (3) The Calan-ESO survey (Ruiz et al. 2001) (4) SuperCOSMOS-RECONS proper-motion survey of the entire southern sky (Henry et al. 2004; Subasavage et al. 2005a, 2005b; Finch et al. 2007; Boyd et al. 2011), (5) the Southern Infrared Proper-Motion Survey (SIPS; Deacon et al. 2005), (7) Lepine's SUPERBLINK survey of a portion of the southern sky (Lepine 2008) and (8) UCAC3 proper motion survey (Finch et al. 2010, 2012).) Then we identified these stars in our CCD observations in a 2-step approach. For each individual exposure we establish a list of HPM stars which could be present in that field. HPM star positions were calculated for the epoch of that exposure and then matched with the individual RA,Dec observations of that exposure to identify and flag HPM stars on each exposure (object type = 3). Contrary to UCAC3, this time a UCAC4 based solution for mean position and proper motion was attempted for all stars including the HPM stars. The results were analyzed as follows: The position and proper motion solution obtained by the above procedure was substituted by zero proper motion and the mean CCD data position at mean observational epoch for the following cases: - PM solution failed or shows large errors (>= 500 mas, >= 50 mas/yr) - derived PM is larger than 500 mas/yr in either component - derived central epoch is earlier than 1947 - RA or Dec position difference to CCD data mean position is >= 3 arcsec These stars are thus added to the group of "no proper motion" stars, i.e. those which did not match up with other catalogs to even begin the proper motion calculation. All stars where then checked against the external set of HPM stars. The PM from the external catalog was used for stars with no UCAC4 PM solution and for those where the difference in PM for either component exceeded 40 mas/yr. Thus we trust the external catalog data more than the UCAC4 derived proper motions in those cases. Comparions of UCAC4 based astrometric solutions of stars with about 100 mas/yr or more with external data (2MASS, thanks Rae Stiening) indicated unrealistic proper motions for many such stars in UCAC4 data. Plots of distribution of number of stars as function of UCAC4 proper motion bins showed an overdensity around 100 and 200 mas/yr which could be traced back to blended images or wrong idendifications of stars with NPM and SPM early epoch data in crowded fields. NPM and SPM plates were exposed twice (long and short) with offset between exposures and using an objective grating, enhancing the chances of confusion in crowded fields. In order to mitigate this problem in UCAC4 new object flags were introduced as follows. All stars with object type = 0,1,2 (i.e. those with UCAC4 based solution for proper motions, excluding above described special high proper motion stars handling, Hipparcos and Tycho data, and supplemented stars) and a proper motion larger than 80 mas/yr in either coordinate were picked from the UCAC4. This is a total of about 2.8 million stars. These were matched with the PPMXL (Roeser et al 2010) using a match radius of 4 arcsec with both catalog positions at epoch 2000. The UCAC4 stars not matched with PPMXL in this way were assigned the new object type = 8 (2029306 stars). For the matched stars the proper motion difference vector lenght was calcualted and a threshold set to flag discrepant proper motions with object type = 9. The threshold was set as the lower of 80 mas/yr and (3 times the combined formal errors + 5 mas/yr systematic error floor). This way 689470 stars in UCAC4 obtained the ojt = 9 flag, while 140887 stars were found to have consistent proper motions from this set of stars and no change to UCAC4 data flags were made. Obviously stars flagged with ojt = 8 or 9 should be handled with caution. Many of the ojt = 8 objects can be bogus stars and many of the ojt = 9 stars are likely affected by blended images. Unless external data are consulted to verify UCAC4 results these stars should not be used. 2f) Photometric data -------------------- For each detected image 2 instrumental magnitudes were derived. First, the model magnitude is based on the flux volume of the best-fit image profile model which is also used for the center position result. Second, an aperture photometry magnitude is calculated. In addition to the systematic error corrections applied for UCAC3 (Finch et al. 2010), for UCAC4 a bias correction was applied as a function of the pixel x-coordinate of the image. This bias is caused by the poor charge-transfer efficiency (CTE) of the CCD used for UCAC observations, resulting in image elongation as a function of x. Different bias models were derived for the model and aperture photometry. The APASS 5-band photometry of over 9 million stars (DR2) was utilized to "flatten" the UCAC instrumental magnitudes. The raw instrumental magnitudes are not linear with offsets up to about 0.5 and 0.3 mag at the bright and faint end, respectively. From color-color plots a linear model was adopted to predict UCAC bandpass magnitudes from APASS r and V. The predicted minus observed (model and aperture mags handled separately) UCAC magnitudes were then plotted as fucntion of magnitude and inter- polation polynomials derived. These corrections were then applied to all UCAC instrumental magnitudes. All corrected, instrumental magnitudes were then transformed into the system of Tycho-2 by a simple zero-point correction (Finch et al. 2010), the same way as with UCAC3 data. Photometric results were averaged for stars with multiple CCD observations to arrive at the UCAC4 catalog entries. Nights with poor photometric quality were flagged and not used in the average, unless no other data are available. Note, that "poor photometric" quality for UCAC4 means "really bad" nights, with significant transparency variations due to clouds. The goal was to obtain approximate magnitudes, maybe reliable on the 10% level with differential magnitudes good to about 5%. UCAC is *not* a photometric catalog. The UCAC4 data are supplemented by 2MASS near-IR magnitudes and APASS 5-band optical photometry up to its data release DR6 (June 2012). 3) Properties of the catalog and important notes for the user ------------------------------------------------------------- 3a) Sky coverage ---------------- UCAC4 is an all-sky catalog with at least about 40 stars per square deg anywhere on the sky. The average density of this catalog is over 2000 stars per square deg. There is a color-coded all-sky plot called "ucac4all2.pdf" in the "plots" folder showing the logarithm of the number of stars per box of 0.5 by 0.5 deg on the sky. Blue is low density, red high with green and yellow in between. 3b) Completeness ---------------- UCAC4 like UCAC3 is more complete than UCAC2, including previously omitted "problem" stars and double stars, many of which could be new discoveries. A paper is in preparation about a sample of new double stars found in UCAC4 and the rate of confirmation by speckle observations. For preliminary results see (Hartkopf et al. 2010). The separation limit for double stars in UCAC4 varies as function of brightness of the components and brightness difference. However, some doubles with separations of under 2 arcsec in UCAC3 have been confirmed as real. Those cases are rare and objects within 2 arcsec of each other have generally been merged to at least a blended image in UCAC4. Some 12,000 sources with a separation of less than 2 arcsec remain in UCAC4, of which about half entered through the Hipparcos/Tycho-2 supplement data, which includes double star annex catalogs. Stars fainter than R = 10 with separations larger than 2 arcsec are likely real double stars in UCAC4. UCAC4 also contains observations of some bright stars, as they happened to make it through the pipeline. However, poor data have been substituted by FK6, Hipparcos and Tycho-2 data (in that order of available data). For reduction details on this see section 2b above. Thus UCAC4 should be complete from the brightest naked eye stars to about 16th mag. The following table gives some general statistics about UCAC4 stars: 113780093 total number of stars in UCAC4 (incl. supplement stars) 109921682 with 2MASS identification 106689821 with proper motions 81897551 with 2 epoch PM 27245403 with 3 or more epoch PM 80806744 with 2 or more images from "good fit" CCD observations 48323349 matched with UCAC2 54690 matched with LEDA galaxies 76020 matched with 2MASS extended source catalog 8925 supplemented stars (no CCD obs.) 121350 UCAC4 entries with a matched Hipparcos star ID 104681 UCAC4 entries with CCD obs. substituted by FK6/Hip/Tycho-2 If the computed position error of a star exceeds 500 mas in either coordinate it was set to 500 mas but the star was kept, if at least 2 observations from different CCD observations were matched or the star is either in the 2MASS, SPM or NPM data files. Similarly, the error in proper motion was truncated to 50 mas/yr but respective stars kept in UCAC4 by the same criteria as for large positional errors. Obviously all large error objects need to be handled with caution, and some of these are simply nonexistent. This approach, different to UCAC2, was taken in order to drive up the completeness of UCAC3 and UCAC4 at the expense of slightly greater contamination. For UCAC4 also a lower threshold than for UCAC3 was adopted in image size for failed image profile fit objects. In particular, the larger limits in positional errors deemed acceptable for UCAC3 and UCAC4 accommodate the fainter limiting magnitude, which was possible mainly due to superior handling of dark subtraction in the pixel data. This allowed many low signal-to-noise, real stars to enter the catalog, although with expected large random errors, as compared to UCAC2. 3c) Reference frame ------------------- The astrometry provided in UCAC4 is on the Hipparcos system, i.e. the International Celestial Reference System (ICRS), as represented by the Tycho-2 catalog. Contrary to earlier UCAC releases, the UCAC4 processing included a down-weighting of Tycho-2 stars with V-magnitude fainter than 11.5 by a factor of 1.5 w.r.t. their nominal weight. Any possible deviations of the Tycho system with respect to Hipparcos or the extragalactic radio reference frame are still under investigation. Positions in UCAC4 are given at the standard epoch of Julian date 2000.0, thus the UCAC4 is a compiled catalog. In order to be able to calculate positional errors at any epoch, the central epoch, i.e. the weighted mean epoch of the data (UCAC + early epoch other catalogs) is given. At the central epoch (which varies from star to star and is also different for RA and Dec) the positional error has its smallest value; the one given in the catalog for "sigma position". In most cases this central epoch will be close to the UCAC observational epoch due to the relatively large weight given to the UCAC observations. However, a fair number of stars have a vastly different mean epoch, ranging back to about 1947. Proper motion solutions with central epoch earlier than that were defined as invalid and substituted by other catalog results if available, or only the observed CCD position is reported with no proper motion. The proper motions are given at the central epoch. Positional errors of stars increase according to the errors in the proper motions when going forward or backward in time from the central epoch. 3d) Magnitudes -------------- UCAC4 observational data (CCD exposures) covers the magnitude range of about R = 8 to 16.3 in a 579-642 nm bandpass. However, data from FK6, Hipparcos, and Tycho-2 were used to supplement UCAC4 to create a star catalog complete from brightest stars to about 16th magnitude. The UCAC bandpass is between visual (V) and red (R). The limiting magnitude can vary by about +-0.3 mag from field to field. UCAC4 gives center fit-model magnitudes as well as aperture photometry derived from the same pixel data reductions already performed for UCAC3. Systematic errors in these magnitudes are believed to be below 0.1 mag, which is a significant improvement over the UCAC2 release. Non-linearity of the instrumental magnitudes were calibrated out using APASS photometry for UCAC4. Tycho-2 stars (excluding the faint end) were used to determine the zero-point of the corrected, instrumental magnitudes on a frame by frame basis. However, UCAC observations often were performed in non- photometric sky conditions. Mean magnitudes were derived from CCD frames with indications of "acceptable photometric quality", which is about 50% of the observations. 3e) Additional photometry ------------------------- The UCAC4 observational data are supplemented with 5-band photometry (B,V, g,r,i) from the APASS project (Henden, private comm.) as well as with IR photometry (J,H,K_s) from the Two Micron All Sky Survey, 2MASS (Skrutskie et al. 2006). In addition, magnitudes errors and some flags are provided. For more details see http://www.aavso.org/apass and http://www.ipac.caltech.edu/2mass/releases/allsky/ . 3f) Non-stellar data -------------------- The UCAC4 contains some galaxies, particularly at the faint end. No flag indicating a galaxy or star has been derived from the CCD pixel data; however, a cross reference to the LEDA galaxies (Paturel et al. 2005) and the 2MASS extended source catalog (Skrutskie et al. 2006) has been made and corresponding information is put into the UCAC4 release. The procedure is the same as for UCAC3. Observations of asteroids have been identified and taken out of the main UCAC4 catalog. Individual epoch observations of about 1000 asteroids at multiple epochs have been prepared for publication, but are not part of the UCAC4 release. The observing schedule explicitly avoided all minor planets brighter than about R = 12, except for special observing campaigns to derive masses of asteroids. 3g) Provided utility software ----------------------------- Only some basic access code is included with this release to illustrate the data format and allow conversion of the main binary files to ASCII tables. It is anticipated that 3rd party companies specialized in providing interfaces between various star catalogs and the user will integrate UCAC4 data into their products, as has been the case for UCAC2 and UCAC3. 3h) UCAC reference material --------------------------- The UCAC4 release on DVD also contains a folder with historical data. A copy of the UCAC internet web pages as of January 2012 is provided as well as a complete collection of papers and presentations given about UCAC. Important other papers about data utilized for the UCAC project are given as well. 3i) Arrangement of the data files --------------------------------- The main catalog data are arranged in declination zones of 0.2 degree width, with zone number 1 starting at the South Pole and increasing toward north. There is a separate file for each of the 900 zones. Records in the individual data files are sorted by right ascension. Each record contains the data for one star, 78 bytes of binary integers as described below. As with previous releases, an index file is provided for fast access. The step size along RA for that index file has been significantly reduced to 0.25 degree = 1 minute. These zone data files are split up into 2 directories, south (zones 1 to 379) and north (zones 380 to 900) to fit on the 2-sided DVD. It is recommended that users copy the individual zone files into a single directory on their hard disk drive to simplify all-sky access. 3j) Star identification numbers (name) -------------------------------------- Official UCAC4 star ID numbers should be utilized for identification purposes and for communication with the UCAC team: the UCAC4 star number is of the following format: UCAC4-zzz-nnnnnn where zzz is the 3 digit zone number (form 001 to 900) and nnnnnn the the 6-digit running record number along the zone file. The cross- identification to UCAC2 stars follows the same pattern with zone and record number of the UCAC2 release given in the UCAC4 data. Note, zones numbers in UCAC4 run from 1 to 900 (0.2 deg wide), while zone numbers in UCAC2 run from 1 to 360 (0.5 deg wide), in both cases beginning at the South Celestial Pole (i.e. in order of declination). 3k) Pitfalls for programmers / access code development ------------------------------------------------------ 1. To retrieve the correct proper motions, there is a need to occasionally extract data from the extra u4hpm.dat file, see note 8 section 5a. 2. All fields stored as byte are stored as a signed byte. Some of these fields need to have 128 added to the byte value to get the correct value. See notes 6 and 9 in section 5a below. 3. For stars with errors in proper motion larger than 25.0 mas/yr the error is coded in groups which are then labled as 251,...,254 to fit into 1-byte values. See note 9 in section 5a below. 4. The hipsupl.dat file contains 333 Hipparcos stars that are associated with two (or occasionally three) UCAC4 stars. In such instances, the hipsupl.dat file contains identical Hipparcos data for each UCAC4 star associated with the Hip number. 4) Files contained on the DVD ----------------------------- The double-sided DVD contains this "readme_u4" file and the following directories: access = example access code (Fortran and C), and sample output html = snapshot of web pages of UCAC project, history, pictures papers = some published papers relevant to UCAC, prev.release readme, history plots = all-sky plots (as described in sections 2 and 3 above) u4b = binary data files (northern and southern part on 2 sides of DVD) u4i = index files, supplemental files needed for access code The split between northern and southern part is not even because there are many more stars on the southern than northern hemisphere. Side 1 of the DVD contains zones z380 to z900 in the folder u4b, while the other side of the DVD contains zones z001 to z379 in folder u4b. If you want to operate UCAC4 from hard disk, copy all the zone files (directory u4b from both sides) and the u4i folder to your hard disk. The main catalog data are contained in binary zone files "z001" to "z900", sorted by declination. Each zone is 0.2 degree wide, beginning with z001 at the south celestial pole. Stars are sorted by RA inside a zone file. The format of these binary data files is explained below. The u4i folder contains the following files: hipsupl.dat = additional data from the Hipparcos 2007 release u4hpm.dat = ASCII table for high proper motion stars (see below) u4index.asc = ASCII table index file for each box in RA and each zone u4index.unf = same table unformatted, binary, used by u4access.f u4supl.dat = additional data for supplement and Hipparcos stars u4xtycho = ASCII cross reference to Tycho-2 star numbers zone_stats = ASCII table, summary of zone files The "access" folder contains some Fortran and C code and example output files. For a description see section 6) below. The "plots" folder contains all-sky color plots for number of stars and mean proper motion as function of RA and Dec. The "papers" folder contains important published papers relevant to UCAC and an attempt to capture all papers written by USNO staff about UCAC, as a historic record. There is also a file about the USNO Twin astrograph history, the telescope used for the UCAC project. The "html" folder contains a snapshot of the UCAC web pages as of January 2012 from the following link, which may or may not be available in the future: www.usno.navy.mil/usno/astrometry/optical-IR-prod/ucac Open the html/ucac.html file on the DVD with your browser to get started. 5) Data formats --------------- Binary files in the UCAC4 distribution use the PC-style sequence of bytes. The same byte sequence is also used on recent Mac computers. Some computers (UNIX style) need a flip of bytes for 2 and 4 byte integers. An option for this is build into the access code provided here. 5a) Main catalog zone data files -------------------------------- The data of the first and last zone are also given in ASCII tables (access/z001.asc, z900.asc) to illustrate the format and allow verification of binary file access by the user. That table was generated with the access/u4dump.f code. Columns are separated by commas on z001.asc, while the z900.asc shows the data of the last zone in ASCII with blanks separating the columns. The following shows sample code (Fortran 77) to illustrate the data format, followed by a table describing each data item (column, same order also on the ASCII sample output). After extending some merged flag data there are a total of 53 columns in the UCAC4 zone data files. * items to read from input files INTEGER*4 ra,spd, pts_key,rnm, mcf, rnz INTEGER*2 magm,maga, cepra,cepdc, pmra2,pmdc2 . ,j_m, h_m, k_m, apasm(5), zn2 INTEGER*1 sigmag, sigra,sigdc, sigpmr,sigpmd INTEGER*1 objt,cdf, na1,nu1,cu1, apase(5), gcflg INTEGER*1 icqflg(3), q2mflg(3), leda,x2m CHARACTER string*9 INTEGER icf(9) OPEN (20,FILE=fnu4,ACCESS='direct',RECL=78) ! 1 record per star i = 0 DO i = i + 1 READ (20,REC=i,ERR=99) ! numb. of bytes 78 . ra,spd, magm,maga, sigmag,objt,cdf ! 8 + 4 + 3 = 15 . ,sigra,sigdc, na1,nu1,cu1 ! 2 + 3 = 5 . ,cepra,cepdc, pmra2,pmdc2,sigpmr,sigpmd ! 4 + 4 + 2 = 10 . ,pts_key, j_m,h_m,k_m, icqflg, q2mflg ! 4 + 6 + 6 = 16 . ,apasm, apase, gcflg ! 10 + 5 + 1 = 16 . ,mcf, leda,x2m, rnm ! 4 + 2 + 4 = 10 . ,zn2, rnz ! 2 + 4 = 6 WRITE (str,'(i9.9)') mcf ! merged catalog flag from 4 byte Int to READ (str,'(9i1)') icf ! 9 individual catalog flags ENDDO 99 WRITE (*,'(a,i9)') 'last record number in file = ',i-1 col byte item fmt unit explanation notes --------------------------------------------------------------------------- 1 1- 3 ra I*4 mas right ascension at epoch J2000.0 (ICRS) (1) 2 5- 8 spd I*4 mas south pole distance epoch J2000.0 (ICRS) (1) 3 9-10 magm I*2 millimag UCAC fit model magnitude (2) 4 11-12 maga I*2 millimag UCAC aperture magnitude (2) 5 13 sigmag I*1 1/100 mag error of UCAC magnitude (3) 6 14 objt I*1 object type (4) 7 15 cdf I*1 combined double star flag (5) 15 bytes 8 16 sigra I*1 mas s.e. at central epoch in RA (*cos Dec) (6) 9 17 sigdc I*1 mas s.e. at central epoch in Dec (6) 10 18 na1 I*1 total # of CCD images of this star 11 19 nu1 I*1 # of CCD images used for this star (7) 12 20 cu1 I*1 # catalogs (epochs) used for proper motions 5 bytes 13 21-22 cepra I*2 0.01 yr central epoch for mean RA, minus 1900 14 23-24 cepdc I*2 0.01 yr central epoch for mean Dec,minus 1900 15 25-26 pmrac I*2 0.1 mas/yr proper motion in RA*cos(Dec) (8) 16 27-28 pmdc I*2 0.1 mas/yr proper motion in Dec 17 29 sigpmr I*1 0.1 mas/yr s.e. of pmRA * cos Dec (9) 18 30 sigpmd I*1 0.1 mas/yr s.e. of pmDec (9) 10 bytes 19 31-34 pts_key I*4 2MASS unique star identifier (10) 20 35-36 j_m I*2 millimag 2MASS J magnitude 21 37-38 h_m I*2 millimag 2MASS H magnitude 22 39-40 k_m I*2 millimag 2MASS K_s magnitude 23 41 icqflg I*1 2MASS cc_flg*10 + ph_qual flag for J (11) 24 42 (2) I*1 2MASS cc_flg*10 + ph_qual flag for H (11) 25 43 (3) I*1 2MASS cc_flg*10 + ph_qual flag for K_s (11) 26 44 e2mpho I*1 1/100 mag error 2MASS J magnitude (12) 27 45 (2) I*1 1/100 mag error 2MASS H magnitude (12) 28 46 (3) I*1 1/100 mag error 2MASS K_s magnitude (12) 16 bytes 29 47-48 apasm I*2 millimag B magnitude from APASS (13) 30 49-50 (2) I*2 millimag V magnitude from APASS (13) 31 51-52 (3) I*2 millimag g magnitude from APASS (13) 32 53-54 (4) I*2 millimag r magnitude from APASS (13) 33 55-56 (5) I*2 millimag i magnitude from APASS (13) 34 57 apase I*1 1/100 mag error of B magnitude from APASS (14) 35 58 (2) I*1 1/100 mag error of V magnitude from APASS (14) 36 59 (3) I*1 1/100 mag error of g magnitude from APASS (14) 37 60 (4) I*1 1/100 mag error of r magnitude from APASS (14) 38 61 (5) I*1 1/100 mag error of i magnitude from APASS (14) 39 62 gcflg I*1 Yale SPM g-flag*10 c-flag (15) 16 bytes 40 63-66 icf(1) I*4 FK6-Hipparcos-Tycho source flag (16) 41 icf(2) .. AC2000 catalog match flag (17) 42 icf(3) .. AGK2 Bonn catalog match flag (17) 43 icf(4) .. AKG2 Hamburg catalog match flag (17) 44 icf(5) .. Zone Astrog. catalog match flag (17) 45 icf(6) .. Black Birch catalog match flag (17) 46 icf(7) .. Lick Astrog. catalog match flag (17) 47 icf(8) .. NPM Lick catalog match flag (17) 48 icf(9) .. SPM YSJ1 catalog match flag (17) 4 bytes 49 67 leda I*1 LEDA galaxy match flag (18) 50 68 x2m I*1 2MASS extend.source flag (19) 51 69-72 rnm I*4 unique star identification number (20) 52 73-74 zn2 I*2 zone number of UCAC2 (0 = no match) (21) 53 75-78 rn2 I*4 running record number along UCAC2 zone (21) 12 bytes --------------------------------------------------------------------------- 78 = 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 UCAC4; 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 = 20 (20000 mmag entry in catalog). Systematic errors are expected to be below 0.1 mag for magm,maga 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 99 for error in magnitude means "no data". 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 (= value 90 in catalog data, unit = 10 mmag). Note (4): The object type flag is used to identify possible problems with a star or the source of data. Of the individual image flags the one with the largest value (worst problem case) is propagated into this object type flag, unless it is superseded by an overriding flag at the combined image stage. The object type flag has the following meaning: 0 = good, clean star (from MPOS), no known problem 1 = largest flag of any image = near overexposed star (from MPOS) 2 = largest flag of any image = possible streak object (from MPOS) 3 = high proper motion (HPM) star, match with external PM file (MPOS) 4 = actually use external HPM data instead of UCAC4 observ.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 PM to PPMXL (see discussion of flags 8,9 in redcution section 2e above) The number of stars with those flags is: 0 103080317 1 2785787 2 15519 3 97042 4 35073 5 5004704 6 34473 7 8925 8 2028600 9 689653 Note (5): The cdf flag is a combined double star flag used to indicate the type/quality of double star fit. It is a combination of 2 flags, cdf = 10 * dsf + dst with the following meaning: dsf = double star flag = overall classification 0 = single star 1 = component #1 of "good" double star 2 = component #2 of "good" double star 3 = blended image dst = double star type, 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 separ. blended image) 5 = case 2 after successful double fit (most likely real double) 6 = case 3 after successful double fit (brighter secondary picked) A word of caution: often a dsf= 1 or 2 image is paired with a dsf= 3. If for a star any of the several images reveals a "blended image", that higher dsf=3 flag is carried into the output file. This can happen for a regular double star with unique components 1 and 2. A flag dsf=3 means this could be component 1 or 2 but at least on one CCD frame a blended image was detected. This blend could be with the other component, or a spurious image or artifact. The double star flags need to be interpreted with caution; anything but a zero means "likely some double star component or blended image". The following number of stars have cdf flag values: 0 110299935 1 262162 2 355769 3 57103 4 2408 14 19590 24 23967 34 1053229 5 7884 15 78344 25 209822 35 1226761 6 23787 16 13096 26 20945 36 125291 Note (6): The range of values here is 1 to 255 which is represented as a signed 1-byte integer (range -127 to 127); thus add 128 to the integer number found in the data file. There is no 0 mas value; data less than 1 mas have been set to 1 mas. Original data larger than 255 mas have been set to 255. If the astrometric data for a star was substituted from an external catalog like Hipparcos, Tycho or high proper motion data, a mean error in position and proper motion depending on the catalog and magnitude of the star was adopted. Note (7): 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 (8): A value of 32767 for either proper motion component means the real PM of that star is larger and found in the extra table file u4hpm.dat (32 stars, ASCII). The cross reference is established by the unique, modified MPOS number (column 51 of main data file), which is also given on the HPM supplement stars file. For stars without valid proper motion the proper motion data are set to 0. However, valid proper motions can also be 0. The "no data" case is indicated by the sigma proper motion columns (see below). Note (9): Values in the binary data files are represented as signed, 1-byte integer (range -128 to 127). Add 128 to bring those values to the range of 0 to 255, which is the error in proper motion in unit of 0.1 mas/yr, with the following exception. Data entries above 250 indicate larger errors as follows: 251 --> 275 = 27.5 mas/yr 252 --> 325 = 32.5 mas/yr 253 --> 375 = 37.5 mas/yr 254 --> 450 = 45.0 mas/yr 255 --> "no data" = set to 500 for output tables 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): The 2MASS items copied into UCAC4 are described at pegasus.astro.umass.edu/ipac_wget/releases/allsky/doc/sec2_2a.html Note (11): 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 (12): The photometric errors from 2MASS were rounded by 1 digit here to fit into fewer bytes (1/100 mag instead of millimag). These data were taken from the j_msigcom, h_msigcom, and k_msigcom columns of the 2MASS point source catalog. See note (10). Note (13): Data are from the AAVSO Photometric all-sky survey (APASS) DR6 plus single observation stars kindly provided by A.Henden. A magnitude entry of 20000 indicates "no data". For bright stars the apasm(1) = B mag and apasm(2) = V mag 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. For the bright supplement stars the same was done. All thses cases are identified by apasm(1) < 20000 and apase(1) = 0 for B mags, and similarly for apasm(2) < 20000 and apase(2) = 0 for V mags. For over 10,000 stars no Vt mag was available and the V mag from Tycho was used instead. The following number of stars have entries in the APASS photometry: 51862350 some valid data in either of the columns 51070044 B mag 51861015 V mag 45799843 g mag 45615993 r mag 41491953 i mag Note (14): Positive errors are from the official release data error estimates (at least 2 observations per star). Formal, S/N estimated errors for single observations are multiplied by -1 for this column. The valid range for each APASS magnitude error is +-90 = +-0.90 mag. For "no data" (i.e. magnitude = 20000 = 20.0 mag) the error is set to 99. Note (15): 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 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 (16, 17) binary data: a single 4-byte integer is used to store the 10 flags of "icf". That 4-byte integer has the value: icf = icf(1)*10^8 + icf(2)*10^7 + ... + icf(8)*10 + icf(9) Note (16): The FK6-Hipparcos-Tycho-source-flag has the following meaning: (= icf(1)) 0 = not a Hip. or Tycho star 1 = Hipparcos 1997 version main catalog (not in UCAC4 data files) 2 = Hipparcos double star annex 3 = Tycho-2 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 8 = FK6 only PM substit. (not in UCAC4 data) 9 = Hipparcos 2007, only proper motion substituted Note (17): 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 = ... same, but involving a flagged double star 3 = multiple match but unique in high confidence level group, no double 4 = ... same, but involving a flagged double star 5 = closest match, not involving a double, likely o.k. 6 = ... same, but involving a flagged double star 7 = maybe o.k. smallest sep. match in both directions, no double 8 = ... same, but involving a flagged double star Note (18): This flag is either 0 (no match) or contains the log10 of the apparent total diameter for I-band (object size) information (unit = 0.1 arcmin) copied from the LEDA catalog (galaxies). A size value of less than 1 has been rounded up to 1. Note (19): 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. Note (20): 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 observ.). For all other stars this unique star identification number is the internal mean-position-file (MPOS) number + 1 million. For both the Hipparcos and the supplement stars there is an entry on the u4supl.dat file providing more information, including the original Hipparcos star number. 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 (21): This info provides a cross reference to UCAC2. Both zn2 and rn2 are 0 if the UCAC4 star could not be found in UCAC2. 5b) Min/max and check sums -------------------------- The following table gives the total range of values in the UCAC4 main data (all zone files from z001 to z900), as well as the value used for "no data". Dashes in the "no data" column indicate that all stars in the UCAC4 catalog have valid entries for that column. col min max no_data description ------------------------------------------------------------------ 1 14 1295999997 --- mean RA [mas] 2 57955 647908447 --- mean SPD [mas] 3 4012 20000 20000 UCAC4 model mag [mmag] 4 4168 20000 20000 UCAC4 aperture mag [mmag] 5 0 99 99 std.err. UCAC4 mag [1/100 mag] 6 0 9 --- object type flag 7 0 36 --- double star flag 8 1 255 255 sigma RAc at central epoch [mas] 9 1 255 255 sigma Dec at central epoch [mas] 10 0 71 --- total number of CCD images 11 0 70 --- n. of CCD images used for mean pos. 12 1 38 --- n. of catalogs (epochs) used for PM 13 4707 10438 --- c. epoch RA [1/100 yr] after 1900 14 4700 10438 --- c. epoch Dec [1/100 yr] after 1900 15 -32603 32767 0 PM RA*cosD [0.1 mas/yr] 16 -31574 32767 0 PM Dec [0.1 mas/yr] 17 3 500 500 sigma PM RAc [0.1 mas/yr] 18 3 500 500 sigma PM Dec [0.1 mas/yr] 19 0 1340037129 0 2MASS star ID number 20 -2989 20000 20000 2MASS Jmag [mmag] 21 -4007 20000 20000 2MASS Hmag [mmag] 22 -4378 20000 20000 2MASS Kmag [mmag] 23 0 58 0 2MASS J icqflag 24 0 58 0 2MASS H icqflag 25 0 58 0 2MASS K icqflag 26 0 99 99 2MASS Jmag error [1/100 mag] 27 0 99 99 2MASS Hmag error [1/100 mag] 28 0 99 99 2MASS Kmag error [1/100 mag] 29 -1087 20000 20000 APASS B mag [mmag] 30 -1440 20000 20000 APASS V mag [mmag] 31 6787 20000 20000 APASS g mag [mmag] 32 5943 20000 20000 APASS r mag [mmag] 33 5030 20000 20000 APASS i mag [mmag] 34 -90 99 99 APASS B mag err [1/100 mag] 35 -90 99 99 APASS V mag err [1/100 mag] 36 -90 99 99 APASS g mag err [1/100 mag] 37 -90 99 99 APASS r mag err [1/100 mag] 38 -90 99 99 APASS i mag err [1/100 mag] 39 0 37 0 gc flag SPM 40 0 9 0 Hipparcos, Tycho source flag 41 0 8 0 catflg AC2000 42 0 8 0 catflg AGK2 Bonn 43 0 8 0 catflg AGK2 Hamburg 44 0 8 0 catflg ZA 45 0 8 0 catflg BY 46 0 8 0 catflg Lick 47 0 8 0 catflg NPM 48 0 8 0 catflg SPM 49 0 99 0 leda galaxy flag 50 0 82 0 2MASS extend.source cat. flag 51 1 182895114 --- unique star ID number, modif. MPOS 52 0 288 0 UCAC2 zone number (if matched) 53 0 270171 0 UCAC2 ID number along zone ------------------------------------------------------------------ The following table lists the check sums (values by column added up over all stars of all zone files): column sum ------------------------ 1 85882199747838282 2 32643520088752491 3 1734468736192 4 1740985078524 5 4308258441 6 50976753 7 92617964 8 7643548652 9 7536811002 10 328481210 11 309920557 12 259941559 13 1032282199626 14 1035570477588 15 -1844702259 16 -2768938466 17 8658847664 18 8631255911 19 72112460953700603 20 1567909305940 21 1515037852115 22 1500861673912 23 758275797 24 759920399 25 766630946 26 482284101 27 589716513 28 805257995 29 2055936882771 30 2006791306640 31 2054419812064 32 2023198315779 33 2028163598478 34 6272154501 35 6276616263 36 6877032078 37 6895992388 38 7370094121 39 202509190 40 8065088 41 6564698 42 444076 43 1533211 44 6258173 45 4320949 46 1413660 47 102261525 48 93499864 49 552401 50 569057 51 9760101273905336 52 7112160417 53 4726488342991 ------------------------ 5c) Other files (in u4i folder) --------------- zone_stats = summary info for each zone This is a text file (ASCII) giving summary information about stars in each zone. There are some header lines describing the contents, followed by a table with 900 lines, 1 each for a 0.2 deg wide zone in declination, beginning at the South Celestial Pole. zn = zone number nsz = number of stars in zone nss = accumulated sum of stars this and prev.zones nopmz = numb. of stars in zone without proper motion no2mz = numb. of stars in zone without 2MASS match max_dec= largest declination of zone zn nsz nss nopmz no2mz max_dec ----------------------------------------------------- 1 206 206 5 3 -89.80 2 660 866 8 17 -89.60 3 1143 2009 16 42 -89.40 ... 898 834 113779410 82 118 89.60 899 512 113779922 39 67 89.80 900 171 113780093 9 20 90.00 ----------------------------------------------------- u4index.asc = index file for each 1 minute in RA This is a text file (ASCII). Each line contains data for an area of sky (bin) 0.2 deg wide in declination (indexed by zone number from 1 to 900), and 1 minute (0.25 deg) wide in RA (indexed from 1 to 1440). So there are a total of 900 * 1440 = 1.296 million lines in this file. The meaning of the columns are: 1 n0 = running star number (index along the main data file) of the star before the first one in this bin, the sequence starts out with 0 at the beginning of each new declination zone 2 nn = number of stars in this bin (which can be zero) 3 zn = zone number (1 to 900) 4 j = index for bins along RA (1 to 1440) 5 dec = upper declination of corresponding zone, printed out only at the beginning of a new zone sample data: n0 nn zn j dec 0 0 1 1 -89.8 0 0 1 2 0 0 1 3 0 0 1 4 0 1 1 5 1 0 1 6 ... 138282 28 450 1438 138310 22 450 1439 138332 26 450 1440 0 23 451 1 0.2 23 31 451 2 54 14 451 3 ... 171 0 900 1438 171 0 900 1439 171 0 900 1440 u4index.unf = same as u4index.asc but as unformatted, binary file: INTEGER*4 n0(900,1440), nn(900,1440) OPEN (15,FILE=fnidxu,ACCESS='direct',RECL=5184000) ! 900 * 1440 * 4 READ (15,REC=1) n0 READ (15,REC=2) nn Thus each item is a 4-byte integer, the first half of the file contains the values for 'n0', the 2nd half contains values for nn. In each half, the data is stored as all values for the particular RA index value for all zones. That is, there is a series of 1440 blocks, with each block containing the values for 900 declination zones. u4hpm.dat = data for very high proper motion stars (ASCII) This file was needed for all stars with a proper motion component outside the +-3276.6 mas/yr range (limit for 2-byte integers). The proper motion in the main data is set to 32767 [0.1 mas/yr] to identify such a case. The star then can be identified by rnm or zn,rnz in this file to pick up the actual proper motion. The file is sorted by running star number. rnm = unique star identifier (col. 51 main data) zn = UCAC4 zone number for this star rnz = running record number along that zone for this star pmrc = actual proper motion in RA*cos(dec) [0.1 mas/yr] pmd = actual proper motion in Dec [0.1 mas/yr] RA = col. 1 of main data file (redundant) SPD = col. 2 of main data file (redundant) maga = col. 4 of main data file (redundant) rnm zn zrn pmrc pmd RA SPD maga 1 644 101666 41087 31413 1140226325 463469832 20000 2 644 101659 41558 32586 1140206623 463496356 20000 200137 137 116044 -37758 7655 782744223 98353832 20000 ... 106363470 469 47857 -37060 -11490 734876481 337245686 14457 110589580 486 52878 -38420 -27250 590832393 349252344 13155 113038183 494 48937 10990 -51230 442763714 355581607 12513 u4supl.dat = data for supplement stars and cross reference to Hipparcos This ASCII file contains all UCAC4 stars which have a match to the Hipparcos catalog and all stars which are supplemented, i.e. those without UCAC CCD observations (bright stars). There are 128631 lines (unique stars) in this file. These are exactly all those stars with unique star number (col.51 of the main data) rnm < 1,000,000. 1 0 0 0 7 0 2 0 0 0 7 0 3 0 0 3 7 0 4 0 0 3 7 0 ... 7019 0 0 3 7 0 7020 0 0 3 7 0 7021 0 0 3 7 0 200001 0 43636 2 7 0 200002 0 107949 2 7 0 200003 0 115928 2 7 0 ... 321607 181870335 11767 7 6 3 321608 181882163 101884 6 3 0 321609 181883754 3128 7 3 0 321610 181888489 47953 7 3 0 col explanation 1 rnm = unique star ID number from UCAC4 (col. 51 main data) 2 MPOS = mean position file (CCD data) internal record number, or zero if not observed with UCAC astrograph 3 hipn = Hipparcos Catalogue star number 4 htsf = FK6-Hipparcos-Tycho source flag (see note 15 main file) 5 objt = object type flag (see note 4 main file) 6 stfl = substitute flag, accumulated from following cases: 0 = no substitute data, use UCAC if available, else external data, else replace UCAC position, proper motion by external data because of: 1 = no "good" image from CCD observation 2 = star is flagged as blended image 4 = position difference to external data is too large (> 50 mas) hipsupl.dat = Hipparcos data, 2nd release (van Leeuwen, 2007), ASCII, for all Hipparcos stars identified in UCAC4 data This file contains 121610 lines (stars) with Hipparcos data linked to the "rnm" unique star ID number of UCAC4 (col. 51 of main data). The rnm for those stars are in the range between 200,001 and 321610. The file contains the following columns. For more explanations see (van Leeuwen, 2007, or cdsarc.u-strasbg.fr/viz-bin/Cat?I/311). col explanation 1 rnm = unique star ID number from UCAC4 (col. 51 main data) 2 MPOS star number (internal running number all mean position stars) note: stars supplemented (no CCD observations) have MPOS = 0 3 original Hipparcos star ID number 4 solution type flag new reductions 5 ... old ... 6 number of components 7 RA [hour] at epoch 1991.25 on ICRS 8 Dec [deg] ... 9 parallax [mas] 10 proper motion RA*cosDec [mas/yr] 11 proper motion Dec [mas/yr] 12 formal error on RA [mas] 13 ... Dec [mas] 14 ... parallax [mas] 15 ... PM RAc [mas] 16 ... PM Dec [mas] 17 number of field transits used 18 goodness of fit 19 percentage rejected data 20 cosmic dispersion added (stochastic solution) 21 entry in one of the supplement catalogs 22 Hipparcos magnitude (Hp) 23 error of Hp 24 scatter of Hp 25 reference to variability annex 26 (B-V) color index 27 formal error on (B-V) 28 (V-I) color index For 109 of these stars there are no 2007 solution Hipparcos data and corresponding columns are set to zero. u4xtycho = cross reference to Tycho-2 This ASCII text file contains 2549788 lines and is sorted by column 2. col explanation 1 Tycho-2 star number (all 3 parts together in single, long integer) 2 (UCAC4 zone number) * 1,000,000 + UCAC4 record number along zone 3 rnm = unique star ID number from UCAC4 (col. 51 main data) 6) Description of utility software ---------------------------------- Fortran code and sample output is provided in the folder "access". There are 2 main programs (u4dump.f and u4access.f) and some additional files with subroutines. Compile string examples are given in the comment section on top of each main program file. The programs can be run from the command line interactively with instructions provided. u4dump.f = read binary zone file(s), output all data items to ASCII file with optional column separator character u4access.f= example code to access UCAC4 data as function of RA,Dec,mag range and output with various formats; utilizing the index file u4sub.f = file with subroutines used in u4dump and u4access u4.tab = sample output from a run of u4access z001.asc = sample output in ASCII of first zone, comma as column separator z900.asc = sample output in ASCII of last zone, blank as column separator These algorithms were also translated into C thanks to Bill Gray (Project Pluto, Guide software, www.projectpluto.com/ucac4.htm), who provided the following files: makefile, u4test.c, ucac4.c, ucac4.h This C code has the same functionality as the Fortran code explained above. 7) Acknowledgments ------------------ In a project such as this that has spanned over more than a decade and two continents, many people have been involved. Here we list people and their main contributions to the project. Norbert Zacharias - Principle Investigator, observer, responsible for UCAC position reductions (from pixels to positions on the sky), observing schedule, and external position comparisons, re-processing of pixel data and development of reduction pipeline, Star-Scan plate measure reductions. Ted Rafferty - former project lead, instrumentation specialist, observer, main author of the astrograph history document. Charlie Finch - re-reduction of CCD x,y to RA,Dec, including systematic error control, high proper motion stars, match to 2MASS and photometric calibration. Marion Zacharias - quality control, observer, early position reductions, extragalactic link program. Terry Girard - SPM data reductions, from x,y plate data to RA,Dec, incl. systematic error handling (magnitude equations) and all related reduction pipeline development. Bill van Altena - for many years of collaboration in astrometry. Burton Jones, Bob Hanson, and Arnold Klemola - NPM data. Arne Henden - for sharing unpublished APASS data and photometric consulting. Dave Monet - measurements of SPM and NPM plates on PPM at NOFS. Nigel Hambly - for collaboration on high proper motion stars and big contributions to UCAC3 proper motions. Gary Wycoff - proper motions data preparation, star identifications (up to UCAC3). Sean Urban - proper motions of UCAC2 release, preparation of other position catalogs including systematic error removal and compiling a merged catalog of Hipparcos and Tycho data. Valeri Makarov - reduction of AGK2 and other StarScan plate measures from global x,y to individual RA,Dec positions. Jennifer Bartlett - assisting in taking out original PMM x,y measures mapping parameters to arrive at raw x,y data of NPM plates Brian Mason, Bill Hartkopf - new double star speckle observations with USNO 26in and data reductions. Bill Hartkopf and Marion Zacharias - preparing the history section of the UCAC4 DVD release. David Hall - verification of tape archive, early data handling. Marvin Germain - telescope control system software development, software-to-hardware interface including electronics. Ellis Holdenried - telescope control system software maintenance and extension of user interface for telescope operation. Lars Winter - basis for astrometric CCD reduction software. Greg Hennessy - computer administration support (USNO-DC) Danilo Castillo - observer, Cerro Tololo, Chile Mauricio Martinez - observer, Cerro Tololo, Chile Sergio Pizarro - observer, Cerro Tololo, Chile Oscar Saa - telescope manager, Cerro Tololo, Chile Trudy Tilleman - observer, U.S. Naval Observatory Flagstaff Station, assist with data reductions. Stephanie Potter - observer, U.S. Naval Observatory Flagstaff Station. Dominic Marcello - observer, U.S. Naval Observatory Flagstaff Station. Gary Wieder - telescope upgrades, relocation, maintenance, and troubleshooting. John Pohlman - telescope upgrades, maintenance, and troubleshooting. John Bowles - telescope upgrades and maintenance (USNO-DC). Dave Smith - telescope upgrades and maintenance (USNO-DC). Tie Siemers - telescope upgrades and maintenance (USNO-DC). Mike Divittorio - telescope maintenance and troubleshooting (NOFS). Steve Sell - telescope maintenance and troubleshooting (NOFS). Albert Rhodes - telescope maintenance and troubleshooting (NOFS). Blaize Canzian - network and computer system support (NOFS). Sumit Dutta - summer student working on separating out minor planet observations and streak artifacts. Aleida Young - summer student working on identification of high proper motion stars. Danley Hsu - summer student working on UCAC3 release, and providing the UCAC3 access code, assist with checking of UCAC4. Other Acknowledgments --------------------- This project would not have been possible without support from the USNO administration. Special thanks are given to Thomas Corbin for under- standing the need for such a project, articulating it to those with resources, and administering the project in its early days. Thanks are given to the three USNO Astrometry Department Heads during the UCAC project. Without their continued support, it would not have come to fruition. They are F. Stephen Gauss, Ted Rafferty, and Ralph Gaume. Thanks are given to the USNO Scientific Director, Kenneth Johnston, for his approval and support of the project and for making USNO resources available. Our successful stay at the Cerro Tololo Interamerican Observatory would not have been possible without a memorandum of understanding, worked out by P. Kenneth Seidelmann, USNO, and the then director of CTIO, Malcolm Smith. The entire staff of CTIO is thanked for their generous support. The same holds for all the people at the Naval Observatory Flagstaff Station (NOFS) during the northern hemisphere observing of UCAC, in particular we want to thank the then director Jeff Pier. Also, we wish to thank Gary Sims from Spectral Instruments for building our 4k camera and providing outstanding support over the years. Finally, we wish to acknowledge the following for their important contributions; Bill Gray for custom updates to his GUIDE software regarding minor planet ephemerids, and Rae Stiening (Univ.of Mass.) for providing preliminary and pre-release 2MASS data to our project. We are grateful for the many, constructive comments we received from the following testers of the UCAC4-beta data: Rae Stiening (from 2MASS) Dave Herald, Dave Gault (Australia) Rama Teixeira (Sao Paulo, Brazil) Christine Ducourant (Bordeaux, France) Bill Gray (Project Pluto) Steve Preston (from occultation community) Ricky Smart (Torino, Italy) Sean Urban, Greg Hennessy, Paul Barrett (USNO) Bob Zavala (NOFS) Aladin and Vizier were invaluable tools provided through CDS, Strasbourg. 8) References ------------- This list includes items cited in the above text and is supplemented by listing all publications related to UCAC production and presentations. Many of the papers listed here can be found in the "papers" subdirectory on the distribution DVD with the aim to document the history of the project. Boyd,M.R., Winters,J.G., Henry,T.J., et al. 2011, "The solar neighborhood XXV. Discovery of new proper motion stars with 0.40 "/yr > mu > 0.18 "/yr between declinations -47 and 00", AJ 142, 10 (2011AJ....142...10B) Deacon,N. R., Hambly,N. C., Cooke,J. A. 2005 "Southern infrared proper motion survey. I. Discovery of new high proper motion stars from first full hemisphere scan" A&A, 435, 363 (2005A&A...435..363D) ESA 1997, "The Hipparcos and Tycho Catalogues", European Space Agency, publication SP-1200 (Cat. I/239) Finch,Charlie T., Henry,Todd J., Subasavage,John P., Jao,Wei-Chun, Hambly,Nigel C., 2007, "The Solar Neighborhood. XVIII. Discovery of New Proper-Motion Stars with 0.40".yr-1>pm>= 0.18".yr-1 between Declinations -90deg and -47deg", AJ, 133, 2898 (2007AJ....133.2898F) Finch,C., Zacharias,N., Girard,T., Wycoff,G.L., Zacharias,M.I. 2009, "UCAC3 is coming!" AAS Finch,C., Zacharias,N., Wycoff,G., 2010, "UCAC3 atrometric reductions", AJ 139, 2200 (2010AJ....139.2200F) Finch,C., Zacharias,N., Henry,T., 2010 "UCAC3 Proper Motion Survey. I. 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E., Corbin,T. E., Wycoff,G. L., Martin,J. C., Jackson,E. S., Zacharias,M. I., Hall,D. M. 1998, "The AC 2000: The Astrographic Catalogue on the System Defined by the HIPPARCOS Catalogue" AJ, 115, 1212 (1998AJ....115.1212U; Cat. I/247) Urban, S.E., Wycoff, G.L., Makarov, V.V., 2000, "Comparisons of Tycho-2 Catalogue Proper Motions with Hipparcos and ACT", AJ 120, 501 (2000AJ....120..501U) Urban,S.E., Corbin, T.E., Wycoff, G.L., Makarov, V.V., Hoeg, E., Fabricius, C., 2000, "The AC 2000.2 Catalogue", AAS meeting 199, abstract #129.04 (Cat. I/275) Urban,S.E., Zacharias,N., Wycoff,G.L, 2004, "The UCAC2 Bright Star Supplement", Vizier on-line data catalog I/294, 2004yCat.1294....0U van Altena, W. F., Girard, T. M., Platais, I., Kozhurina-Platais, V., Ostheimer, J., Lopez, C. E., and Mendez, R. A., 1999, "The Yale/San Juan Southern Proper Motion Program", AAS DDA meeting #31, #10.04 Wielen,R., Schwan,H., Dettbarn,C., Lenhardt,H. Jahreiss,H., Jahrling,R., 1999, "Sixth Catalogue of Fundamental stars (FK6)", Veroeff. Astron. Rechen-Inst. Heidelberg 35, 1 (Cat. I/264) Winter, L. 1999 Ph.D thesis, University of Hamburg (in German), CCD image reductions Zacharias, N. 1997, "Astrometric Quality of the USNO CCD Astrograph (UCA)", AJ 113, 1925 (1997AJ....113.1925Z) Zacharias, N., Germain, M.E., Rafferty, T.J., 1997, "UCAC-S: a New High Precision, High Density Astrometric Catalog in the Southern Hemisphere", in: Proceedings "Hipparcos Venice 97", ESA publication SP-402, p.177 Zacharias,N. "Extension of the optical reference frame: ground based", IAU GA 1997, JD7, invited review talk in Highlights of Astronomy, Vol.11A, p.300-303, ed. J.Andersen, Kluver Acad.Publ. 1998 Zacharias,N. Corbin,T.E. Zacharias,M.I Rafferty,T.J. Seidelmann,P.K. Gauss,F.S., 1998 (BAAS 30 No.4, p.1368) "High Precision Astrometry for the Hubble Deep Field - South", poster preseted at the AAS meeting #193, Austin, TX, Jan. 1999 Zacharias, N. Zacharias, M.I., 1999, "Data Structure and Software of the UCAC-S Project", in: Proceedings of ADASS VIII, Eds. D.M.Mehringer, R.L.Plante and D.A.Roberts, ASP Conf.series 172, p.345, San Francisco Zacharias,N. Urban,S.E. 1999, "The first year of the UCAC-S project", AAS, DDA meeting #31, paper #10.05 Zacharias, N., Urban, S.E., Zacharias, M.I., Hall, D.M., Wycoff, G.L., Rafferty, T.J., Germain, M.E., Holdenried, E.R., Pohlman, J., Gauss, F.S., Monet, D., Winter, L., 2000, "The first US Naval Observatory CCD Astrograph Catalog", AJ 120, 2131 (2000AJ....120.2131Z; Cat. I/268) Zacharias, N., Zacharias, M.I., Urban, S.E. and Hoeg, E., 2000, "Comparing Tycho-2 astrometry with UCAC1", AJ 120, 1148 (2000AJ....120.1148Z) Zacharias,N., Rafferty,T.J., Urban,S.E., Zacharias,M.I., Wycoff,G.L. 2000, "The UCAC as input catalog for FAME", proceed. IAU Coll. 180, p.80, Washington, DC, Eds. K.J.Johnston, D.D.McCarthy, B.J.Luzum, G.H.Kaplan Zacharias,N., Zacharias,M.I., Rafferty,T.J. 2001, "Status of the UCAC project", abstract, DDA meeting #32, Houston, TX Zacharias, N., 2002, "Astrometric surveys in support of large telescopes", Proceed. SPIE 4836, 279, Eds. T.A. Tyson & S. Wolff Zacharias,N., Zacharias,M.I., Urban,S.E., Rafferty,T.J. 2002, "UCAC2: a new high precision catalog of positions and proper motions", abstract, AAS meeting 199, Washingtion DC, Jan. 2002 Zacharias,N., Zacharias,M.I. 2002, "Systematic error corrections for UCAC2 positions", presentation at the DDA meeting, Mt.Hood Zacharias, N. 2003, "The USNO CCD Astrograph Catalog (UCAC) Project and Beyond", in "Small Telescopes in the New Millennium II. The Telescopes We Use.", ed. T Oswald, Kluwer Acad. Publ Zacharias, N., Urban, S., Rafferty, T., Holdenried, E., and Winter, L., 2003, "First Results from AGK2 Plate Remeasurements", BAAS 35 #4, p.1036, abstract #6.01, 34th DDA meeting Ithaca, NY Zacharias,N. 2004, "Astrometric reference stars: from UCAC to URAT", proceed. 3rd Potsdam Thinkshop on robotic telescopes, AN 325, 631 (2004AN....325..631Z) Zacharias,N., Urban,S.E., Zacharias,M.I., Wycoff,G.L., Hall,D.M., Monet,D.G., Rafferty,T.J. 2004, "The Second US Naval Observatory CCD Astrograph Catalog (UCAC2)" AJ 127, 3043 (May) (2004AJ....127.3043Z; Cat. I/289) Zacharias,N., Zacharias,M.I. 2007, "The USNO CCD Astrograph Catalog (UCAC)", poster for USNO display (unpublished) Zacharias,N., Finch,C., Wycoff,G., Hartkopf,W. "Improving Hipparcos Proper Motions with UCAC", DDA meeting 2009, Virginia Beach, 2009, BAAS 41 No.2, p. 910, abstract #16.03 Zacharias, M.I., Zacharias, N. 2009, "Significant radio-optical reference frame offsets from CTIO data", poster paper at the IAU XXVII Gen.Ass., Rio de Janeiro, Brazil Zacharias,N., Finch,C., Girard,T., Hambly,N., Wycoff,G. Zacharias,M.I., Castillo,D., Corbin,T. et al. 2009yCat.1315...0Z, data release of UCAC3, CDS catalog I/315, Aug 2009 Zacharias,N. 2010, "UCAC3 pixel processing", AJ 139, 2208-2217 (2010AJ....139.2208Z) Zacharias,N., Finch,C., Girard,T., Hambly,N., Wycoff,G., Zacharias,M.I., Castillo,D., Corbin,T., DiVittorio,M., Dutta,S., Gaume,R., Gauss,S., Germain,M., Hall,D., Hartkopf,W., Hsu,D., Holdenried,E., Makarov,V., Martines,M., Mason,B., Monet,D., Rafferty,T., Rhodes,A., Siemers,T., Smith,D., Tilleman,T., Urban,S., Wieder,G., Winter,L, Young,A., 2010 "The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)", AJ 139, 2184-2199 (2010AJ....139.2184Z; Cat. I/315) Zacharias,N. Gaume,R. 2010, "UCAC and URAT: optical astrometric catalog observing programs", proceed. Journees meeting Paris 2010 (in press) Ed. N.Capitaine, http://syrte.obspm.fr/jsr/journees2010/index.php?page=proceedings Zacharias,N., Finch,C., Zacharias,M.I., Girard,T. 2011, "UCAC4 status", poster paper presented at the AAS 218, Boston,MA ------------------------------------------------------------------- Enjoy UCAC4 and Live Long And Prosper ! Norbert Zacharias for the UCAC team, USNO, Washington DC, July 2012 -------------------------------------------------------------------