SKY2000 MASTER STAR CATALOG* Joanne R. Myers, Christopher B. Sande, and Alvin C. Miller** Wayne H. Warren, Jr.*** David A. Tracewell**** Abstract: The SKY2000 Master Star Catalog is a completely revised and enhanced version of the old SKYMAP catalog that has been in use during the last 2 decades for spacecraft acquisition and tracking applications. The previous release of this catalog, still called SKYMAP at the time, included new astrometric data and improved and extended (near-infrared) photoelectric photometric observations and better data for multiple stars. Changes made to produce the current SKY2000 catalog include reprocessing of the photovisual and photographic magnitudes and of the double/multiple-star data, ingestion of star identification numbers from the principal astrometric source catalog, propagation of positional errors to the standard catalog epoch, and addition of several fields for new data. Also, individual errors have been detected and corrected. The quality assurance work continues. INTRODUCTION The original SKYMAP Master Star Catalog (Ref 1) was developed to support fixed-head star trackers in spacecraft attitude determination software developed at the National Aeronautics and Space Administration's (NASA's) Goddard Space Flight Center. The original versions were designed as a compilation of stellar objects that would be essentially complete to a blue or visual magnitude of 9.0. Successive versions of the SKYMAP catalog were issued between 1978 and 1993 to correct individual errors discovered in each interim, but the basic catalog content and format remained the same. The development of more accurate star trackers in the late 1980s, especially charge-coupled-device-based detector systems, resulted in the decision to update the catalog to include magnitude and color data in the near-infrared region of the electromagnetic spectrum where charge-coupled devices have their maximum sensitivity. However, several other factors led to the final decision to redesign and build the catalog anew. These factors included the availability of vastly superior and more abundant primary data, the presence of many "derived" data in SKYMAP, inadequate and sometimes erroneous cross identifications, and lingering errors for individual stars (especially multiple systems). The first edition of the rebuilt catalog was called SKYMAP 4.0 (Ref. 2) and its slightly revised successor became SKYMAP 4.0a (Ref 3). Earlier versions of the SKYMAP Master Star Catalog were in binary format, but the new version was prepared entirely in character-coded (alphanumeric) form, which has the advantages of easy access (readability) without specialized software and of being able to store data of identifiable and variable precision in the same field. Thus, the new catalog stores data in an appropriate precision corresponding to their accuracy, and the precision can vary within the same data field. In addition to the removal of many derived data, wideband photometric data in the R (red) and I (infrared) systems were added as new fields. However, the major change in Version 4.0 was the replacement of astrometric (positions and proper motions) data with more accurate values stored at full precision, where appropriate. The current version of the SKYMAP Master Star Catalog (4.1), now renamed SKY2000 Master Star Catalog, includes additional modifications to improve mission support, as well as some reformatted data to comply with standard astronomical practice. The primary objectives for SKY2000 are to: * Improve cross-identification information * Generate more realistic positional errors * Correct and expand double- and multiple-star data * Provide improved reference magnitudes for stars not having photoelectrically measured values * Port the Master Star Catalog and the associated SKY2000 software system from a mainframe to a workstation platform GENERATION OF NEW SKY2000 MASTER CATALOG The following subsections provide additional details on all of the major modifications made to Version 4.0a to produce SKY2000. the current format specifications for the catalog. summarize the statistics of the Master Star Catalog. The final subsection summarizes the work and briefly outlines plans for further enhancements. Incorporation of PPM Numbers into the SKY2000 Master Catalog PPM numbers are the primary identifiers for stars in the Catalogue of Positions and Proper Motions (PPM) (Ref. 4). The SKYMAP Master Star Catalog, Versions 4.0 and 4.0a, contained a data field for the PPM numbers, but the data for this field have only recently been incorporated into the new SKY2000. The PPM - North, PPM - South, and PPM Supplement (Ref. 4) were all used for the PPM number additions and were processed individually. To process the PPM catalogs, common identifiers between the PPM catalogs and the Master Star Catalog were used: the Henry Draper (HD), Durchmusterung (DM), Smithsonian Astrophysical Observatory (SAO), and Dritter Katalog der Astronomischen Gesellschaft (AGK3) numbers. For each identifier type, software utilities were created to find common numbers between the PPM catalogs and the Master Star Catalog, and the PPM number for that star was added to SKY2000. Each utility executed decreased the number of SKY2000 stars with no PPM numbers. After all the identifier types were used for PPM number processing, a final utility was created and used to search for common positions between the PPM catalogs and SKY2000 and to add the PPM number when an exact match in position was found. Out of the 299,510 stars in SKY2000, approximately 294,000 now contain PPM numbers. Approximately 300 stars in SKY2000 can be found in the Bright Star Supplement to the PPM. This separate PPM catalog file contains data for bright multiple stars that do not have accurate astrometric data measurements in the PPM catalog. These stars will need to be processed manually because no common identifiers exist between the Supplement and SKY2000. The majority of the remaining stars in SKY2000 without PPM numbers are not in the PPM catalogs, but a number of problem entries exist--most being for double and multiple stars--that remain to be examined. Photovisual and Photographic Magnitude Reprocessing The photovisual (ptv) and photographic (ptg) magnitudes used in SKY2000 have been obtained directly from the PPM and HD catalogs. The reprocessing was accomplished in three separate steps: 1. Reading the PPM, searching primarily on HD number and secondarily on both SAO number and DM identifier. DM identifiers were tested on catalog, declination zone, and number in zone. In cases where a star does not have an HD number, the SAO and DM entries were considered primary identifiers. Where a matching HD number was found and one or more of the other identifiers differed, the match was considered successful, but a warning message was written to a report file to ensure further examination after processing. 2. Processing a merged catalog, consisting of the HD (Ref. 4) and the HD Extension (Ref. 4), to fill gaps, i.e., magnitudes were sought for cases in which a ptv or ptg magnitude had not been found in the PPM. Again, primary identification was sought by HD number, with only the DM identifier being available as a secondary qualification. Entries with matching HD numbers and differing DM identifiers were considered matches, but a warning message was written to a report file. Only values coded as observed were taken. 3. Reprocessing the HD finding chart (Ref. 4) stars was somewhat different. The general approach was that of gap filling, as in step two. The primary criterion was again the HD number, but a position separation check complemented this test; if it failed, a star would be rejected regardless of its HD number. This approach was followed after initial examination of the input catalogs revealed several stars with matching HD numbers and significantly differing positions. A rejection in this case created output to a report file for later examination. Of the many types of magnitudes listed in the HD chart catalog, only quantities unambiguously identifiable as observed magnitudes were taken. WDS Reprocessing The Washington Catalog of Visual Double Stars (WDS) (Ref. 4) was reprocessed in a single execution run that consisted of two steps. 1. All existing multiple-star data in SKY2000 taken from earlier versions of the WDS were blanked out. 2. The WDS was read for each SKY2000 entry and searched for matches based on DM number. Unfortunately, the WDS does not include alphanumeric catalog prefixes (CD, CP, BD, SD). However, it does follow a convention for DM catalogs based on declination, but in the overlap zones, identification is not certain. Furthermore, the WDS number itself could not be reliably tested because these identifiers have changed with various updates of the catalog and have not, in all cases, been updated in other catalogs that use this identifier. Tests on individual component identifiers are necessarily too complex to deal with all cases that may be encountered. Designing an algorithm with such flexibility is too time consuming and difficult; therefore, the component selection algorithm was limited to cases in which several entries in the WDS have the same DM number. Within these constraints, matches found in the WDS were placed into the output SKY2000 file, overwriting multiple-star information from other sources where present. Warning messages were written to a report file in cases where input WDS numbers differed for the same DM number or where a WDS number did not exist in an input SKY2000 entry matched to a WDS entry. Correction of Individual Errors However intelligent the ingestion software may be for catalog work, miscellaneous errors inevitably will occur. These errors may result from actual errors in the source catalogs or from situations so complex (e.g., double and multiple stars) that computer software cannot deal with them. A varied assortment of such problems had to be reckoned with in the SKY2000 Master Star Catalog, and more will no doubt be encountered as the work proceeds. It may be stated with confidence that almost all of these problems result from stellar duplicity and multiplicity, where component identifiers may be reversed, components could not be adequately identified by computer, or multiple systems were not treated thoroughly in the source catalogs. Propagation of Position Uncertainties to the Year 2000 Position uncertainties in earlier versions of SKYMAP were given at epoch. This was also the case for all astrometric catalogs from which data were extracted for SKYMAP Version 4.0a, except for the Bright Star Catalogue (BSC5) (Ref. 4) and the Bright Star Supplement (BSS) (Ref. 4). These two catalogs contained positional data from established astrometric source catalogs, but no positional uncertainties. For these, the positions were extracted, but average position uncertainties were inserted based on the original source catalogs. For example, all stellar positions in the BSC5 that originated from Catalogue of Positions and Proper Motions (PPM) were given the same average position uncertainty at the mean epoch of observation. With the creation of SKY2000, all position uncertainties were propagated to epoch 2000.0 using the following: the uncertainty at 2000.0 = [the uncertainty at the central epoch of the observations - (t - t(c))**del]**1/2 where t(c) = the uncertainty of the central epoch of the observations del = 2(1-eps) eps = the average uncertainty in proper motion for each source catalog Future plans are to replace all average position uncertainties with actual values extracted from the source catalogs and propagated to 2000.0. SKY2000 STATISTICS Table 2 and Table 3 give the distribution of data based on the source from which the data originated. The source numbers are referenced in ref.dat. Table 4 provides the source distribution of position uncertainties in the Master Star Catalog. Table 5 provides the source distribution of angular separation and magnitude difference for multiple-star systems. Table 1 is the format table that is contained in the ReadMe; Table 6 is ref.dat. SUMMARY AND FUTURE WORK The new SKY2000 Master Star Catalog (SKYMAP Master Catalog, Version 4.1) has been prepared to support spacecraft acquisition and tracking applications. The major enhancements in SKY2000 include improved cross indexing among star designations, propagation of positional error estimates to the current catalog epoch (2000.0) to make them more realistic, improved ptv and ptg magnitudes throughout the catalog, correction of many individual errors present mostly for double and multiple stars, and an improved format with more uniform data fields. In addition, the entire SKY2000 system has been ported from a mainframe to a workstation environment. The position uncertainties will be homogenized in a future version of SKY2000. The astrometry and photometry will be updated from the European Hipparcos space mission data, new ground-based photoelectric data will be added, all existing red and infrared data may possibly be transformed to the currently used Cousins system, and information for double and multiple stars will be improved. ACKNOWLEDGMENTS The SKY2000 Master Catalog revision was only possible with the help of two Computer Sciences Corporation analysts, N. Ottenstein and S. Abeyagunawardene, who converted software utilities needed for the enhancement effort from the mainframe to the PC and UNIX platforms. REFERENCES 1. D. M. Gottlieb, "SKYMAP: a new catalog of stellar data," Astrophys. J. Suppl., Vol. 38, 1978, pp. 287-308 2. M. A. Slater, Jr., A. C. Miller, W. H. Warren, Jr., and D. A. Tracewell, "The New SKYMAP Master Catalog (Version 4.0)," Astrodynamics 1995, Volume 90 of Advances in the Astronautical Sciences, American Astronautical Society, August 1995, AAS 95-304, pp. 67-81 3. W. H. Warren, Jr., A. C. Miller, J. R. Myers, and D. A. Tracewell, "The New NASA Spacecraft Acquisition and Tracking Catalog," presented at the "Thirty Years of Astronomy at Wesleyan University," conference in Middletown, Connecticut, April 19-20, 1996; to be published in Baltic Astronomy, Vol. 6, pp. 81-88, 1997 4. See ref.dat. --------------------------------------------------------------------------- * This work was supported by NASA's Goddard Space Flight Center in Greenbelt, Maryland, under contract NAS5-31000. ** Computer Sciences Corporation, Applied Research Department, 10110 Aerospace Road, Lanham-Seabrook, Maryland, 20706 USA. Telephone: 301-794-1000. E-mail: Joanne.Myers@cscgt.gsfc.nasa.gov. *** Hughes STX, 7701 Greenbelt Road, Greenbelt, Maryland, 20770 USA. Telephone: 301-441-4086. E-mail: Wayne.H.Warren.I@gsfc.nasa.gov. **** Goddard Space Flight Center, Flight Dynamics Division, Greenbelt, Maryland, 20771 USA. Telephone: 301-286-3718. E-mail: david.tracewell@gsfc.nasa.gov. --------------------------------------------------------------------------- Table 2 PRELIMINARY SOURCE CATALOG DISTRIBUTION (1 of 2) Source Position/b Proper Rad. Par. V-mag/b B-mag/b U-mag/b ptv ptg No. Motion Vel. (p) mag mag 1(98) 14 2(98) 88508 28915 6(98) 1318 11(98) 4755 [15] 4648/1 2295 295 70 780 [16] 282692/20 278348 2 122062 150177 [17] 4780/8 3727 [18] 560/99 471 [19] 284 61 24 [20] 29375/ 29951/ 25689/ 2109 2145 1859 [24] 20/1 82/4 18/4 [25] 13 9087 9093 2899 8629/7 9026/5 7528/5 [26] 1 1493 254 2453/32 2200/27 1770/21 [27] 4879/589 4996/617 1 [28] 31 [29] 737 664 [30] 795 8 [31] 362 <32> 13/2 <33> 31 8 4 4 <34> 417 6 <35> 8 3 4832 <37> 1 <39> 1 1 1 <40> 6 6 3 <41> 6 7 4 <42> 62 62 51 4 <52> 1430/7 640 <53> 1 <55> 1 <60> 1 61 1 1 94(98) 12770 219/1 95(98) 1553 97(98) 3832 1 99 6 Totals 37 299510/135295399 15642 4548 60143/ 47821/ 35226/ 210573 183924 2740 2798 1889 NOTES /b = number blended (98) = data included through SKYMAP Master Star Catalog, Version 3.7 [ ] = new sources for Version 4.0 < > = new sources for Version 4.0a All other sources added for new SKY2000 Master Star Catalog Table 2 PRELIMINARY SOURCE CATALOG DISTRIBUTION (2 OF 2) Source MK 1D Multiplicity Variability Pass 1 Pass2 2 No. Spectral Spectral Type Class 3(98) 46 4(98) 3 3 [10] 69213 54 [15] 72 [16] 34855 [18] 857 [19] 614 1053 28451 [20] 1751 42 [21] 1/1 1/1 [23] 23556 26 [24] 2 24 [25] 8770 2 1473 822/7 2 2455/13 79 [26] 2088 5 51 [27] 1 55 152 5 13481/ 2038 [28] 22 2225 4 44 [29] 41508 [30] 400 60 2584 <36> 1 <38> 1 <39> 6 43 1 44 1 <60> 1 95(98) 88 96(98) 216371 98(MK) 10090 Totals 27 116495 294210 30911 4962 832/8 13481/ 2 2500/14 79 2038 NOTES /b = number blended (98) = data included through SKYMAP Master Star Catalog, Version 3.7 [ ] = new sources for Version 4.0 < > = new sources for Version 4.0a All other sources added for new SKY2000 Master Star Catalog Passband 1: Johnson-R; Russian/b-R; Cousins-R Passband 2: Johnson-I; Cousins-I Table 3 PRELIMINARY SOURCE CATALOG DISTRIBUTION (DERIVED V' MAGNITUDES) Derived V' Magnitude Observed Input Data 234541 Converted HD/AGK3 ptv and ptg, or ptv, or ptg (spectral class) 4225 Unconverted HD ptv and ptg, or ptv 4 B and MK spectral type [Standard (B-V)] 4 B and HD/AGK3 spectral class [adopted average (B-V) in that class] 591 B and HD/AGK3 ptg [adopted average (B-V) = + 1.00 over all classes] Total = 239365 Table 4 DISTRIBUTION OF POSITION UNCERTAINTIES FOR SELECTED SOURCES Source 0- 0.1- 0.2- 0.3- 0.4- 0.5- 0.6- 0.7- 0.8- 0.9- 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1-2 2-3 3-4 >10 Totl 15 15322080 1036 4648 16 124018 9838 29 148807 282692 17 4181 460 84 31 13 3 4 4 4780 18 412 99 49 560 19 284 284 25 3 10 13 29 2 80 117 144 52 24 80 118 27 3 89 1 737 33 25 1 3 1 1 31 34 417 417 35 8 8 37 1 1 40 6 6 41 6 6 42 62 62 52 1430 1430 55 1 1 60 1 1 61 1 1 2 97 1 1 3830 3832 Total 1611127634 10993 5183 149440109 111 180 30 10 94 1 1 4114 299510 Table 5 DISTRIBUTION OF ANGULAR SEPARATION OF COMPONENTS FOR MULTIPLE STARS IN ARCSECONDS Source 0-1 1-2 2-3 3-4 4-5 5-10 10-2020-30 30-45 >45 Total 18 12 2 2 2 5 20 130 152 115 365 805 19 7231 3686 22161546 1241 3866 3460 1776 1054 1773 27849 24 3 5 4 2 3 17 25 1387 6 3 1 5 10 12 10 9 1443 26 16 2 1 1 1 2 4 1 10 38 27 3 2 2 8 9 8 19 51 Total 8649 3696 22231549 1248 3897 3615 1957 1190 2179 30203 Back to Top