DESCRIPTION OF XZ CATALOG OF ZODIACAL STARS David W. Dunham, Wayne H. Warren Jr. 1994 June 18 The XZ catalog was created at the U. S. Naval Observatory in 1977 by Richard Schmidt and Tom Van Flandern, primarily for the purpose of generating predictions of lunar occultations, and for analyzing timings of these events. It was designed to include all stars from Robertson's Zodiacal Catalog (ZC), the SAO catalog, and the AGK3 catalog that are within 6d 40' of the ecliptic, which is as far as the Moon's limb can ever get as seen from anywhere on the Earth's surface, leaving some margin for stellar proper motions and change in the obliquity of the ecliptic over the course of three centuries. Hereafter, this region will be called "the Zodiac". The catalog contains 32,221 entries. Two years after the catalog was created, and observations were already reported using its numbers, it was found that about 200 stars near the equator from the AGK3 catalog were outside the Zodiac, and a similar number that should have been included were not. Since the numbering system had already been established, the catalog was not changed to correct this deficiency. Over the years, some errors in the catalog, due mainly to errors in the SAO and AGK3, were corrected. A few stars with very bad data were "eliminated" by changing their declination to -89d and adding 40 to their magnitudes. In 1986, most of the stellar positional data were replaced with improved data from Harrington's and Douglass' Zodical Zone (ZZ) catalog, which used for its observing list SAO stars in the Zodiac (actually, broader than the XZ Zodiac since ecliptic latitudes to +/-15d were used) north of declination approximately -25d. The positional data for many of the stars south of declination -25d with right ascensions greater than 18h were improved with data from the Lick Voyager Uranus catalog. In 1991, the photographic magnitudes of the AGK3 stars not in the SAO were converted to photovisual magnitudes by applying corrections based on the star's spectral type, when available. Stellar magnitudes and double-star codes have been updated periodically based on reports from observers. Each time a series of updates was made, the XZ version was changed. The current version is XZ80N, created during the summer of 1992. Late in the summer of 1992, Mitsuru Soma in Japan created a J2000 version of the XZ, which we call XZ80NJ2. The next update is planned for late 1994, when the positional data may also be replaced with PPM data; probably only the J2000 version will be updated. The XZ catalog is no longer maintained at the U. S. Naval Observatory (USNO); it is now maintained by the International Occultation Timing Association (IOTA). The changes made to the different versions of the XZ catalog during the past several years have been documented in the Occultation Newsletter, IOTA's quarterly publication. Note that the XZ catalog contains no decimal points in the numeric fields, only numbers or blanks. The F-formats given below indicate where the implied decimal point is located. ---------------------------------------------------------------------- Fd Datum Byte(s) Description Format ---------------------------------------------------------------------- 1 XZ 1- 6 "X" and sequential number A1,I5 2 DM 7- 14 Durchmusterung identifier A1,I2,I5 3 DSC 15 Double-star code (*) A1 4 Mag 16- 18 Visual magnitude F3.1 5 RA 19 27 Right ascension (B1950.0*) hms 2I2,F5.3 6 PM RA 28- 33 Proper motion in RA (s/century) F6.3 7 Dec 34- 42 Declination (eq & ep B1950.) d'"(*) A1,2I2,F4.2 8 PM Dec 43- 48 Proper motion in Dec ("/century) F6.2 9 Parallax 49- 51 Trigonometric parallax(",0 no data) F3.3 10 RV 52- 55 Radial velocity (km/sec; 0 no data) I4 11 Cat code 56- 57 Second catalog code (*) I2 12 Cat number 58- 62 Second catalog number I5 13 SAO 63- 68 SAO Catalog number (*) I6 14 Sp. type 69- 71 Spectral type A3 15 RA error 72- 74 Error in RA (", at epoch) F3.2 16 PM RA error 75- 77 Error in RA PM (") F3.2 17 Dec error 78- 80 Error in Dec (", at epoch) F3.2 18 PM Dec error 81- 83 Error in Dec PM (") F3.2 19 Epoch 84- 86 Epoch - 1850 (integer years) (*) I3 20 Name-1 87-103 Star name or catalog designation A17 21 Name-2 104-105 Star name or catalog designation(*) A2 22 Name-3 106-108 Star name or catalog designation(*) A3 23 Name-4 109-110 Star name or catalog designation(*) A2 24 Encoding 111 Encoding for bytes 104-110 (*) I1 25 Source code 112-113 Source catalog code (*) I2 ---------------------------------------------------------------------- Notes (*): ---------- 1. Double-star codes Listed below are the double star codes currently in use. For "triple," three stars are usually meant, but there may be other known stars in the system. A - Listed by Aitken and/or Burnham (ADS, BDS) B - Close double with third star nearby with separate XZ number C - Listed by Innes, Couteau, or other visual observers D - Primary of double; secondary has separate XZ entry E - Secondary of double; primary has separate XZ entry F - Following component G - A or C with second star either M, J, U, or V and third star referred to second star H - Triple: J, U or V and M I - O with secondary either J, U, or V (third star's data referred to secondary) J - Single-lined spectroscopic binary; separation probably <0.01" K - U or V, but duplicity doubtful ("possible" double) L - Triple: J or U, and V; or all V; or all J M - Mean position of close pair N - North component O - Orbital elements available P - Preceding component Q - Triple: J or U or V, and O R - Triple: O and O S - South component T - Triple: V and A or C; or all A and/or C U - Separation <0.01" (usually 2-line spectroscopic binary) V - Separation >0.01", but not visual (occultation, interferometric, or speckle component) W - Triple: J or U, and A or C X - Probably a close double, not certain Y - Triple: K or X, and A or C Z - Triple: O and A or C or V or X or L $ - M with secondary either M, J, U, or V (third star's data referred to secondary star) 2. The epoch and equinox of the Right Ascension and Declination have been B1950 for most of the history of the XZ. In 1992, Mitsuru Soma at the National Observatory in Mitaka, Japan, made a J2000 version of XZ80N, where the epoch and equinox of the R.A. and Dec. were converted to J2000 from B1950 using the Astronomisches Rechen-Institut's procedure for this conversion. 3. Declination (and Right Ascension) The declinations can be read into one double-precision variable with an F9.2 format, rather than with a format such as given (separate variables for d,',"), although the sign is always in byte 34 (in several copies of the XZ distributed previously on magnetic tape by USNO and IOTA, the sign was not always in byte location 34, and it was necessary to use the F9.2 format rather than the format given in the table; see the 3rd paragraph under "Other USNO lunar occultation catalogs" below). Save the original read-in value (so it can be tested at the end for the sign), then take its absolute value for decoding into degrees, minutes, and seconds of arc. A subroutine like the Fortran function SECNDS can be used convert the full number into seconds of arc counted from the equator; it can similarly be used to convert the right ascensions into seconds of time, 0 - 86400, counted from the equinox, by reading the R.A. as one double-precision number with an F9.3 format rather than with the format indicated. 4. Second catalog codes 80 AGK3 (not ZC, not SZ; the second catalog code number in this case is the number of the star in the AGK3 zone, which can be determined from the degrees of declination for the B1950 version of the catalog; for these stars, the AGK3 zone and number are also given in the name fields. If the encoding = 5, see note 9, then the AGK3 zone and number are not given in the name field, an example being X00002.) 90 ZC (Zodiacal Catalog, USNO Astronomical Papers Prepared for the use of the American Ephemeris and Nautical Almanac, Vol. X, Part II, by James Robertson, U.S. Gov't Printing Office, Washington, 1940) 94 SZ (SAO, not ZC; the SZ was a Zodical subset of the SAO catalog, a predecessor of the XZ which was replaced by the XZ) 5. SAO numbers. "0" means that the star is not in the SAO catalog, mainly for stars whose data were obtained from the AGK3. In the Zodiac, the SAO numbers are always greater than 50,000. So the SAO field was used for the AGK3 error code, which ranges from 1 to 16. If the second catalog code is 80 and the SAO number is within the range of 1 to 16, the SAO number is actually an AGK3 error code. 6. Epoch. This is the mean epoch of the observations that should be used only for calculating the error in the star's position at a specified time when using the errors in fields 15-18. 7. Source catalog codes 10-60 XZ/SAO 69 XZ/GC 70 SAO/GC (very poor data) 76 XZ/GC 80 AGK3/XZ 81 ZC/Perth 70 (combined ZC and P70 data) 82 Yale 84 Lick Voyager catalogs (usually combined with SAO data) 90 ZC/XZ 91 FK4 92 FK4 Supplement/FK3 93 N30 96 Pleiades catalog (Eichhorn) 97 ZZ87 (Harrington and Douglass) 98 Perth 70 8. Star names Note that the star names sometimes extend into the coding field when there is no code present. The codes give information on source catalogs and their numbers. Fields 20 to 23 can just as well be read as a single field with A24. Field 21 is a code if byte location 108 is blank; if byte location 108 is not blank, then field 21 is the end of the star name. If one wants only the star names and not the code, byte location 108 must be tested for blank; if it is blank, then field 21 should be replaced with two blank bytes. The star names do not always follow the current I.A.U. or Bright Star Catalog conventions. For example, X05652's (ZC 648's) name is given as DELTA TAURI, when it is actually Delta 1 Tauri, and no Bayer designation is given for Delta 2 Tauri (=X05687 = ZC 653 = 64 Tauri). Similarly, X05546's (ZC 628's) name is given as OMEGA TAURI, when it should be Omega 2 Tauri, and no Bayer designation is given for Omega 1 Tauri (=X05396 = ZC 614 = 43 Tauri). The authors are interested in learning of other name errors so that they can be corrected in the planned PPM version of the XZ. In some cases, the old 4-character constellation abbreviations are used. Also, one should take care not to confuse Flamsteed number designations, such as 13 Tauri, with numbers given from some obscure old catalogs, such as 13 B. Tauri (from Bode's catalog). Other old catalogs used are Gould (G.), Heis (H1.), and Hevelius (H.). In some cases, the old catalog had the star in a different constellation than it actually is in according to the I.A.U. boundaries. In these cases, old catalog constellation name is given in parentheses, followed by a slash(/), followed by the name of the constellation in which the star is really located. The constellation names are given in the genetive form, if not abbreviated. 9. Star names and Encoding. Field 20 is always the first part of the star name. The use of fields 21-23 differ according to the number in the Encoding column (byte location 111), which can have either of the four values listed below: Encoding Use of Fields 21-23 1 Field 21 = 2nd part of star name. Field 22 = 3rd part of star name. Field 23 = 4th part of star name. 2 For SAO stars whose source is ZZ87 (see "97" under Note 7): Field 21 = 97 (the source catalog code). Field 22 = b00, where b = blank; this can be ignored. Field 23 = number of plates used for positional information. For non-SAO AGK3 stars: Field 20 = AGK3 followed by 13 blanks (1st part of star name). Field 21 = AGK3 declination zone, always less than 97. Field 22&23 = AGK3 number in the declination zone. 3 & 5 Field 21 = 2nd part of star name. Field 22 = 3rd part of star name. Field 23 = Field 25 (Source catalog code). Other USNO lunar occultation catalogs. David Dunham created other star catalogs for special occultation predictions at USNO; these have a format similar to that of the XZ, where the character in byte location 1 identified the catalog, when field 1 was included. In 1977, the K-catalog was created just before the XZ, to include AGK3 and southern Yale catalog stars (a few hundred, some as bright as 7th mag., were not in the SAO catalog, and therefore not in the SZ, since no proper motions were given for them) that were not in the SZ catalog being used at the time. It included over 7000 stars to supplement the SZ. In 1978, after the XZ was established and used for occultation predictions, the K-catalog was modified so that it would exactly supplement the XZ, but without changing the sequence, since predictions had already been distributed and observations reported using K-catalog numbers in 1977. Most (but not all) of the AGK3 stars in the K-catalog are also in the XZ, so these were "removed" (at least for lunar occultation prediction purposes) by changing the degrees of declination of these stars in the K-catalog to -89. So although there are still over 7000 entries in the K-catalog, only several hundred of them are valid; other users may simply want to remove the invalid entries by rejecting all stars with declinations less than -88d. The other catalogs do not cover the whole Zodiac, but only certain fields of special interest, such as galactic clusters and star fields that were traversed by the Moon during total lunar eclipses. These catalogs include stars down to 11th and 12th magnitude usually obtained from the Astrographic Catalogs. They were cross-referenced with the XZ, and the data of matched stars replaced with XZ data; the X or ZC number for such stars was given in the DM field #2, which for these catalogs must be read with the format A3,I5 since non-numeric data are sometimes included in all byte locations of the "zone". The occultation prediction program at USNO required stars be located at every hour of right ascension. Therefore, "spacer" entries were needed for these catalogs to fill this requirement. The magnitudes of these false-star entries were given as either 40 or 50 and the declinations as either -89d or -90d. Be careful when using the declinations from these other catalogs, since unlike the XZ, the sign of the declination is not always in byte location 34. The declinations should be read with an F9.2 format, since the minus for negative declinations is not always in byte locations 34 or 35. Save the original read-in value (so it can be tested at the end for the sign), then take its absolute value for decoding into degrees, minutes, and seconds of arc. A subroutine like the Fortran function SECNDS can be used convert the full number into seconds of arc counted from the equator; see the appendix below. The other catalogs are listed below. Logical Physical Occultation Cat. Record Record Newslet. Ref. Name Length Length Vol./No./pages Brief description 5BM 80 8000 1/4/29-31 For 1975 May lunar eclipse 2/4/37 M, mainly for 1979 eclipses 3/1/3 B, for 1981 eclipses "5BM" is an RA-sorted combination of the above 3 catalogs E 86 8600 3/12/249 & For eclipses in 1985 and 1986 3/16/345 J 104 10400 1/13/138-139 Hyades, Milky Way, 1977 eclipses, & 1/14/145-147 & 1/16/170 other clusters C 104 10400 2/14/188-189 Milky Way, 1982 eclipses, clusters & 2/16/222-224 K 86 8600 1/13/138-139 See above L 86 8600 4/11/263-266 1989-90 eclipses, Lick-Voyager cats. & 4/12/301 & 4/14/336 The above describes the format of the 113-byte records in the normal export version of the XZ catalog. However, different variations on this format have been used for internal use at the U. S. Naval Observatory and for the other catalogs. They are descibed below, for the different logical record lengths involved. Record Length Description 80 Includes fields 2-19 described above, that is, byte locations 7 - 86. 86 Includes fields 1-19 described above, that is, byte locations 1 - 86. The first byte location contains the single-letter USNO catalog code identifier (E, K, etc.). 104 Includes fields 2-23 described above, that is, byte locations 7 - 110. The C and J catalogs use this format, and some of the records at the end of the catalog (at least for C) are blank. For the C and J catalogs, the name fields (20 and 21) are all blank. There is no encoding in the name fields of these catalogs. Since the 80- and 104-byte versions do not include field 1 (XZ number), the sequential number must be obtained by couting entries (logical records) from the beginning, first entry = X00001, second = X00002, etc. (or first = C00001, second = C00002, etc. for the C-catalog, etc.). We acknowledge useful comments and information provided by Mitsuru Soma that have made this documentation more comprehensive and accurate. If additional information about the XZ catalog is needed, contact Dr. David W. Dunham, IOTA, 7006 Megan Lane, Greenbelt, MD 20770-3012, Telephone: 301-953-5609; E-mail: dunham@nssdca.gsfc.nasa.gov APPENDIX. A double precision function Fortran routine SECNDS is mentioned above; it converts a packed number in sexigessimal form, HHMMSS.SSS for R.A.'s and +/-DDMMSS.SS for declination, into a pure count of seconds from the origin. Another double precision function, SEX, does the inverse transformation from pure seconds to the packed sexigessimal form. These subroutines are listed below. Double Precision Function Secnds (A) C Convert D,M,S or H,M,S into seconds Double Precision A,B,C J = IDINT (1.D-4 * (A + DSIGN (1.D-4,A))) L = IDINT (A + DSIGN (1.D-4,A)) K = L - 10000 * J M = 40 * (90*J-K/100) + K B = M C = L Secnds = B + A - C Return End Double Precision Function Sex(X) C Convert number in seconds to sexigessimal form C X is in seconds. This function is the inverse of Secnds Implicit Real*8(A-H,O-Z) Data Ist/0/ If (Ist .gt. 0) Go to 10 Ist = 1 G = 1.D0 / 60.D0 H = G * G 10 A = DABS(X) B = A * H I = IDINT(B) C = I C C is integer degrees or hours A = A - 3600.D0 * C B = A * G I = IDINT(B) D = I C D is integer minutes A = A-60.D0 * D Sex = 10000.D0 * C + 100.D0 * D + A If (X .lt. 0.D0) Sex = -Sex Return End ------------------------------------------------------------------------ End of Description DWD, WHW 1994 June ==============================================================================