Sixth Orbit Catalog: Format

The format of the Sixth Orbit Catalog was extensively modified in March 2005, in order to 
address a couple shortcomings in the original format. First, some users of the catalog 
requested that published formal errors for orbital elements be included when available. 
Also, new techniques such as long-baseline interferometry have in recent years yielded 
orbits with ever shorter periods and smaller semi-major axes. The range in these values 
(for example, periods >100,000 years on the one extreme, periods quoted to 0.00000001 
years or less at the other) did not fit in the number of characters initially allocated.

Accordingly, the master file was widened considerably to accommodate both formal errors 
and higher precisions. Flags have been added to the period and semi-major axis columns, 
allowing periods to be quoted in units ranging from centuries to minutes, semi-major axes in 
milliarcseconds and microarcseconds as well as arcseconds, and T0 in Julian date and MJD 
as well as fractional Besselian year. 

The web catalog now uses two lines per orbit, in order to decrease the width to a 
manageable level. Errors are placed immediately below each element, and some catalog names 
(such as HD and Hipparcos) and other items are similarly stacked. A blank line follows 
each orbit.

The format is as follows:

LINE  COLUMN  FORMAT       DESCRIPTION
  1     1     2I2,F5.2,    epoch-2000 right ascension (hours, minutes, seconds).
              A1,2I2,f4.1  epoch-2000 declination (degrees, minutes, seconds).
        2     A10          WDS designation (based on arcminute-accuracy epoch-2000 
                           coordinates).
        3     A14          Discover designation and components, or other catalog 
                           designation.
        4     I6           HD catalog number.
        5     A1,F5.2,A1   Magnitude of the primary (usually V) and flags preceding and 
                           following:
                                > = fainter than quoted magnitude
                                < = brighter than quoted magnitude 
                                v = variable magnitude
                                k = magnitude is in K-band or other infrared band
        6     F12.6,A1     Period (P) and code for units:
                                m = minutes (rarely used)
                                h = hours (rarely used) 
                                d = days
                                y = years
                                c = centuries (rarely used)
        7     F9.5,A1      Semi-major axis (a) and code for units:
                                a = arcseconds
                                m = milliarcseconds (mas)
                                M = arcminutes (used only for alp Cen + Proxima Cen)
                                u = microarcseconds (uas - not yet used)
        8     F8.4         Inclination (i), in degrees.
        9     F8.4,A1      Node (Omega), in degrees. An identified ascending node is 
                           indicated by an asterisk following the value.
       10     F12.6,A1     The time of periastron passage (T0) and code for units:
                                c = centuries (fractional year / 100; used only for alp Cen + Proxima Cen) 
                                d = truncated Julian date (JD - 2,400,000 days)
                                m = modified Julian date  (JD - 2,400,000.5 days)
                                y = fractional Besselian year
       11     F8.6         Eccentricity (e).
       12     F8.4,A1      Longitude of periastron (omega), in degrees, reckoned from the 
                           node as listed. If the published omega value is later determined
                           to fall in the wrong quadrant, the value is flipped by 180deg;
                           a letter "q" indicates the quadrant has been corrected.
       13     I4           Equinox, if any, to which the node refers.
       14     I1           Orbit grade (to nearest integer), as previously discussed.
       15     A1           A link "N" to any notes for this system. 
       16     A1           A link "P" to a figure illustrating the orbit and all data for 
                           this object currently tabulated in the WDS database. Symbols 
                           used in these figures are as in Figure 1.
       17     A1           A link "E" to appropriate entries in the ephemeris file.
       18     A8           A code for the reference (usually based on the name of the 
                           first author and the date of publication), with a link to a 
                           reference file.

  2     3     'ADS ',I5    ADS (Aitken Double Star catalog) number.                                                                 
        4     I6           Hipparcos catalog number.
        5     A1,F5.2,A1   Magnitude of the secondary and flags as noted above for primary 
                           magnitude
        6     F12.6        Published formal error in P. Units are the same as for P.
        7     F8.5         Error in a. Units are the same as for a.
        8     F8.4         Error in i.
        9     F8.4         Error in Omega.
       10     F12.6        Error in T0. Units are the same as for T0.
       11     F8.6         Error in e.
       12     F8.4         Error in omega.
       13     I4           Date of the last observation used in the orbit calculation, if 
                           published.

  3                        blank line (separator)



Columns in the ephemeris file are as follows: (updated 6 Jul 2015, following discussion with users)

 COLUMN  FORMAT            DESCRIPTION    
    1     A10              WDS designation, as above.
    2     A14              Discoverer designation, as above.
    3     I1               Orbit grade, as above.
    4     A8               Reference code, as above.
    5     5(F5.1,F7.3,4X)  Predicted values of theta and rho for the years 2014-2018. 
       or 5(F5.1,F8.4,3X)  Theta is given in degrees and rho in arcseconds. Rho values for
                           a given pair are listed to 1mas precision unless at least one 
                           predicted value for that pair is under 10mas. In this case all 
                           values for the pair are listed to 0.1mas precision.
    6     A20              Text indicating astrometric orbit or pair with incomplete 
                           elements. Rho values are those of the photocenter relative 
                           to the barycenter for astrometric solutions. Obviously no 
                           theta or rho values are listed for pairs with incomplete 
                           elements.


Finally, a plain ASCII test version of the catalog is included, with one (long) line of 
information for each orbit. The format for this file is as follows:

 COLUMN  FORMAT           DESCRIPTION    
    1    T1,2I2,F5.2,     epoch-2000 right ascension (hours, minutes, seconds).
         A1,2I2,f4.1      epoch-2000 declination (degrees, minutes, seconds).
    2    T20,A10          WDS designation (based on arcminute-accuracy epoch-2000 
                          coordinates).
    3    T31,A14          Discover designation and components, or other catalog 
                          designation.
    4    T46,I5           ADS (Aitken Double Star catalog) number.
    5    T52,I6           HD catalog number.
    6    T59,I6           Hipparcos catalog number.
    7    T66,A1,F5.2,A1   Magnitude of the primary (usually V) and flags preceding and 
                          following:
                            > = fainter than quoted magnitude
                            < = brighter than quoted magnitude 
                            v = variable magnitude
                            k = magnitude is in K-band or other infrared band
    8    T73,A1,F5.2,A1   Magnitude of the secondary and flags as noted above for primary 
                          magnitude 
    9    T81,F12.6,A1     Period (P) and code for units:
                            m = minutes (not yet used)
                            h = hours (rarely used) 
                            d = days
                            y = years
                            c = centuries (rarely used)
   10    T95,F10.6        Published formal error in P. Units are the same as for P.
   11    T106,F9.5,A1     Semi-major axis (a) and code for units:
                            a = arcseconds
                            m = milliarcseconds (mas)
                            M = arcminutes
                            u = microarcseconds (uas - not yet used)
   12    T117,F8.5        Error in a. Units are the same as for a.
   13    T126,F8.4        Inclination (i), in degrees.
   14    T135,F8.4        Error in i.
   15    T144,F8.4,A1     Node (Omega), in degrees. An identified ascending node is 
                          indicated by an asterisk following the value.
   16    T154,F8.4        Error in Omega.
   17    T163,F12.6,A1    The time of periastron passage (T0) and code for units:
                            d = Julian date (-2,400,000 days)
                            m = modified Julian date (MJD = JD-2,400,000.5 days)
                            y = fractional Besselian year
                            c = "centuries" (year/100 for extremely long-period orbits)
   18    T177,F10.6       Error in T0. Units are the same as for T0.
   19    T188,F8.6        Eccentricity (e).
   20    T197,F8.6        Error in e.
   21    T206,F8.4        Longitude of periastron (omega), in degrees, reckoned from the 
                          node as listed.
   22    T215,F8.4        Error in omega.
   23    T224,I4          Equinox, if any, to which the node refers.
   24    T229,I4          Date of the last observation used in the orbit calculation, if 
                          published.
   25    T234,I1          Orbit grade (to nearest integer), as previously discussed.
   26    T236,A1          A flag "n" to any notes for this system. 
   27    T238,A8          A code for the reference (usually based on the name of the first 
                          author and the date of publication).
   28    T247,A18         Name of image file (png format) illustrating orbit and all 
                          associated measures in the Washington Double Star database.