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    Sixth Catalog of Orbits of Visual Binary Stars: format of text version

The format of the Sixth Orbit Catalog has been extensively modified, 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).

The format of the text version of the Sixth Catalog 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 
    4    T46,I5           ADS (Aitken Double Star catalog) number.
    5    T52,I6           HD catalog number.
    6    T59,I6           Hipparcos catalog number.
    7    T67,F5.2,A1      Magnitude of the primary (usually V), and flag:
                            > = fainter than quoted magnitude
                            < = brighter than quoted magnitude 
                            v = variable magnitude
                            k = magnitude is in K-band or other infrared band
                            ? = magnitude is uncertain
    8    T74,F5.2,A1      Magnitude of the secondary (usually V), and flag:
                            > = fainter than quoted magnitude
                            < = brighter than quoted magnitude 
                            v = variable magnitude
                            k = magnitude is in K-band or other infrared band
                            ? = magnitude is uncertain
    9    T82,F11.6,A1     Period (P) and code for units:
                            m = minutes (not yet used!)
                            h = hours (not yet used!)
                            d = days
                            y = years
                            c = centuries (rarely used)
   10    T95,F10.6        Published formal error in P (in same units as for P). 
   11    T106,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)
   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. If 
                          the ascending node is later determined to off by 
                          180deg, it is flipped, and a "q" code added to 
                          indicate the change. 
   16    T154,F8.4        Error in Omega.
   17    T163,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  (MJD = JD-2,400,000.5 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,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.
   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, ranging from 1 ("definitive") to 5 
                          ("indeterminate"). Additionally, a grade of 8 is used
                          for interferometric orbits based on visibilities 
                          rather than rho and theta measures (hence not gradable
                          by the present scheme) and a grade of 9 indicates an
                          astrometric binary (also lacking rho and theta data).
   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 

Columns in the ephemeris file (orb6ephem.txt) are as follows: 
(Note: ephemeris file was updated 6 Jul 2015, following discussion with users)

 column   format               description
    1     A10                  WDS designation, as above.
    2     T12,A14              Discoverer designation, as above.
    4     T28,A8               Reference code, as above.
    5     5(F5.1,F7.3,4X)      Predicted values of theta and rho over a 5-year   
       or 5(F5.1,F8.4,3X)      timespan. 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     T116,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