Sixth Orbit Catalog: Format

The format of the Sixth Orbit Catalog 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 centuries or days as well as years, semi-major axes in 
milliarcseconds as well as arcseconds, and T0 in modified Julian date as well as 
fractional Besselian year. (Codes for other units, such as periods in hours or semi-major 
axes in micro-arcseconds, will be added as needed).

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:

    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 
    3    T31,A14          Discover designation and components, or other catalog 
    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 
                            > = 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 
    9    T82,F11.6,A1     Period (P) and code for units:
                            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)
   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 = modified Julian date (JD - 2,400,000 days)
                            y = fractional Besselian year
   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 
   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.