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
designation.
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
database.
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
elements.