Sixth Catalog of Orbits of Visual Binary Stars
Note: The following description is adapted from a paper by Hartkopf et al. (2001 AJ 122,
The Sixth Catalog of Orbits of Visual Binary Stars continues the series of
compilations of visual binary star orbits published by William Finsen, Charles Worley,
and Wulff Heintz from the 1930's to the 1980's. As of 15 July 2013 the new catalog
included 2,425 orbits of 2,331 systems. All orbits have been graded as in earlier
catalogs, although the grading scheme was modified as of the Fifth Catalog to be more objective. Ephemerides are
given for all orbits, as are plots including all associated data in the Washington
Double Star (WDS) database. A subset of orbits potentially useful for scale calibration
is also presented.
It should be noted that a version of the Sixth Catalog, containing orbits published
through 30 June 2006, is one of five USNO double star catalogs written to CD-ROM.
Copies of this CD-ROM are available upon request.
The Sixth Catalog of Orbits of Visual Binary Stars (henceforth Sixth Catalog
; Hartkopf et al. 2001a) continues the series of compilations of visual binary star
orbits previously published by Finsen (1934, 1938); Worley (1963); Finsen & Worley (1970);
Worley & Heintz (1983, henceforth Fourth Catalog); and most recently by Hartkopf,
Mason, & Worley (2001b, henceforth Fifth Catalog).
The 3+ decades since publication of the Fourth Catalog have seen revolutionary
changes in the field of visual double star work, primarily through the advent and
maturation of interferometry. Speckle interferometry, especially on large telescopes,
can produce astrometric results of very high accuracy (down to milliarcsecond level), even
for systems much closer and of shorter period than those available to micrometry and other
visual techniques. Although the speckle technique has been known since 1970, it did not
produce data in significant quantity until about 1975; at the time of publication of the
Fourth Catalog only a handful of orbits had been calculated in which speckle played
much of a role. Now, however, speckle interferometry is a mature field, and nearly all
orbits published since the 1980's have included speckle results, some exclusively.
Long-baseline interferometry [e.g., Mark III (cf., Pan et al. 1990) and the Navy Prototype
Optical Interferometer (NPOI; cf., Hummel et al. 1998)] is now perhaps in a similar degree
of maturation as was speckle in 1983; an increasing number of binaries once exclusively
the "property" of spectroscopists are now the targets of multi-aperture telescope arrays.
Indeed, the distinction between the spectroscopic and visual regimes will
largely disappear in the coming decades, as the magnitude sensitivity of these new
interferometers improves. Catalogs such as this will have to evolve as well; as
spectroscopic + visual "combined solutions" go from being rare to commonplace, the
argument for publishing only a subset of a binary's elements will grow increasingly
artificial. For the present, however, information on combined solutions is relegated to a
GRADING THE ORBITS
A major consideration in the production of a new catalog is the determination of grades
for each orbit. The Fourth Catalog grading scheme was based on orbital coverage,
number of observations, and their overall quality, and presented on a numerical scale
(1=definitive to 5=indeterminate - see Figure 1 for examples) based on the accumulated
experience of the authors and their qualitative assessment of individual observers. (It
should be noted that Worley and Heintz had some six decades' worth of combined experience
at the time they published the Fourth Catalog; these two gentlemen also rank as the
third and second most prolific binary star observers of all time.) While useful for
judging the reliability of a given orbit, this scheme was rather subjective, and therefore
difficult to duplicate by catalogers having less experience. For the Fifth Catalog
we attempted to devise a more objective grading scheme, based on the same information as
that available to Worley and Heintz. This same grading scheme is used for the Sixth
Catalog as well.
Figure 1: Two examples each of grade 1 (left) and grade 5 (right) orbits. Factors used in
determining these grades are discussed below. In these and all other orbit figures in this
catalog, green plus signs indicate visual (micrometric) observations, violet asterisks
photographic measures, and blue symbols various interferometric techniques (open circles,
filled circles, and filled squares for eyepiece interferometry, speckle or other
single-aperture techniques, and multi-aperture techniques, respectively). Finally, a red
"H" or "T" indicates a measure from Hipparcos or Tycho. The dot-dash line indicates the
line of nodes. Scales are in arcseconds, and the curved arrow at lower right indicates
the direction of orbital motion.
Evaluating the Observations
In order to determine rms residuals, we first must determine relative weights to be
assigned to each observation. The following factors were considered:
The best method we really have for evaluating the quality of an observation is to see how
it compares with others. In practical terms this means we examine the size of the orbit
residuals it gives. Here we unfortunately are stuck with a bit of a circular argument:
in order to assign weights to observations we must compare them to orbits. Yet in order
to determine those orbits in the first place we must assign weights to the observations!
The way in which we chose to minimize this problem was by sheer force of numbers - by
examining many well-observed binaries whose orbits are generally acknowledged to be of
- telescope aperture
- binary separation
- magnitude and magnitude difference: Since we are mainly interested in relative
weights to be assigned for observations of a given binary, these factors are presumed
constant and we have ignored them.
- "number of nights": Some observers publish individual measures, while others average
2 or more into means. A simple sqrt(N) term handles this.
- expertise of the observer: This is the most difficult factor to evaluate. Accuracy
should improve with experience, but may decrease as, for example, a visual observer's
eyesight deteriorates with age (some observers produced measurements for 40, 50, and
even 70 years). We have ignored this age factor for the present, however.
- other factors, such as systematic errors in a given piece of equipment, quality of the
scale calibration, seeing conditions at a given site, etc.: These are ignored as
separate factors, but obviously are part of the "observer expertise" factor.
All grade 1 and 2 orbits from the Fourth Catalog were examined, together with all
more recently published orbits and numerous long-period orbits (such as GRB 34 in Figure
1). This last group was included in order to evaluate observers of wider systems. Many
of these systems show small orbit residuals over the covered orbit arc, although the
lack of phase coverage earns them a poor grade. From ~750 orbits and over 100,000
observations initially examined, some 450 orbits and ~66,000 observations were chosen for
evaluation of observer weights.
Since the number of "degrees of freedom" is large, we simplified the problem in two ways:
Figures 2 and 3 illustrate some of our initial findings on accuracy versus separation for
the different techniques. Both theta and rho residuals show obvious
dependence on separation. The long-known fact that separations of very close systems are
systematically overestimated is also apparent, especially in Figure 2a. Assuming
(drho/rho)^(-2) gives a reasonable estimate of the relative weight of an
observation, we fit a polynomial to (drho/rho)^(-2) versus
rho/rho_lim for each technique to determine this first weighting factor as
a function of separation and telescope aperture.
- Since binary resolution is a function of telescope aperture, we remove this
complication by scaling separation to the Rayleigh limit of the telescope used
(rho_lim ~ L/D, where L is the wavelength and D
is the telescope diameter. Assuming L = 550nm, rho_lim =
0.136/D, for rho_lim in arcseconds and D in meters).
- Different observing techniques - micrometry, photography (including conventional CCD
observations), and interferometry (plus adaptive optics, satellite observations, and
other high-resolution techniques) - were evaluated separately. All data for a given
technique were first studied, then relative weights for observers using that
Figure 2: O-C errors in (left) relative separation and (right) position angle, versus
separation (scaled to each telescope's Rayleigh limit).
Figure 3: O-C separation errors versus separation, for (left) visual, (center)
interferometric, and (right) photographic observing techniques. The relative accuracies
of the three techniques are apparent.
As a second step, we wish to determine the relative qualities of each observer who uses a
given technique. We do this by removing the overall error versus separation fit derived
above, then determining rms residuals for each observer. Observers having too few
measures for individual weighting are averaged together. Relative weights for each
observer are then defined as the inverse square of their rms residual (with the weighted
mean weight for each technique scaled to 1). We find:
As mentioned earlier, the third factor is simply the sqrt(N) term which gives
higher weight to normal points averaged from more than one observation. Finally, a few
measures in the WDS are flagged as being uncertain or of poor quality. The term
W_quality, usually assigned a value of unity, is reduced by half for such measures.
The overall weight of a given observation, then, is determined by the product of these
- Visual observers received a wide range in relative weight, from about 0.1 to 4.5. It
must be noted that this is not really a measure of an observer's competence; a person
who only looks at bright, wide, low zenith-distance, small dm pairs will tend
to receive a better grade than does someone who pushes his instrument to its limits in
magnitude, dm, etc. These more difficult observations are usually the more
- Photographic observers were of fairly uniform quality. Observers having significant
numbers of measures ranged in relative weight from about 0.5 to 1.4, while the
observers making smaller contributions received a weight of 0.3. Since photographic
techniques are presumably somewhat more objective than visual measurement, this
finding seems reasonable.
- Eyepiece interferometry tends to get rather low marks (0.01 to 0.3) compared to other
interferometric techniques. Speckle and other single-aperture techniques garnered
weights of 0.02 to 1.4, with the larger speckle efforts generally receiving the higher
weights. The Mark III received a comparable weight of about 0.9. NPOI received a
very high weight (13.3), but this is rather misleading, as the number of measures is
small and the separation regime of this instrument is such that this is largely an
indication of internal consistency.
W = W_technique (rho, aperture) *
W_observer * sqrt(N_measures) * W_quality
Evaluating the Orbits
Worley & Heintz used the following criteria for each orbit grade (as quoted from the
How can these grades be determined in an objective manner? We evaluated as many of the
928 orbits in the Fourth Catalog as possible, as follows. We extracted from the WDS
the ~100,000 observations made of these objects through 1982 (i.e., the same data
available to Worley and Heintz for their evaluations). After removing orbits without
grades, plus a few problematic orbits and obviously erroneous measures, we were left with
901 orbits and 93,775 observations. We then determined the following statistical factors
for each system:
- 1 = Definitive.
- Well-distributed coverage exceeding one revolution; no revisions expected except for
- 2 = Good.
- Most of a revolution, well observed, with sufficient curvature to give considerable
confidence in the derived elements. No major changes in the elements likely.
- 3 = Reliable.
- At least half of the orbit defined, but the lesser coverage (in number or
distribution) or data consistency leaves the possibility of larger errors than in
- 4 = Preliminary.
- Individual elements entitled to little weight,and may be subject to substantial
revisions. The quantity 3 log(a) - 2 log(P) should not be grossly
erroneous. This class contains: orbits with less than half the ellipse defined;
orbits with weak or inconsistent data; orbits showing deteriorating representations of
- 5 = Indeterminate.
- The elements may not even be approximately correct. The observed arc is usually too
short, with little curvature, and frequently there are large residuals associated with
Some of our results are shown in Figure 4. Data for each grade are spread over three
lines in order to more easily see individual points. Means are listed below the data for
each grade, with vertical lines indicating mean and 1 sigma values. "Outliers"
(removed from the statistics) are plotted in smaller symbols.
- weighted rms residual in separation (dR)
- weighted rms residual in relative separation (i.e., dR/R)
- theta coverage: measures were sorted in order of theta, then the rms
difference in angle [i.e., theta(n) - theta(n-1)] was calculated
- maximum "gap" in theta: also from above theta sort
- phase coverage: calculated from period (P) and periastron epoch (T),
then sorted and rms differences determined as done with theta
- maximum "gap" in phase (Why analyze both theta and phase coverage? While
both position angle and phase are equivalent for a circular, face-on orbit, position
angle coverage becomes increasingly meaningless for inclinations approaching 90
degrees, while uniform phase coverage may undersample periastron passage for a
- number of revolutions from first to last observation
- total number of observations
Figure 4: Fitting WH4 grades to rms residuals and other factors, as described in the text.
As is apparent in both the orbit examples in Figure 1 and the Figure 4 results, no one
factor alone is sufficient for determining the grade. For example, some poorer orbits
show very small separation residuals (as evidenced by the turnover in the rms
dR/R plot for grades 4 and 5); the extremely long period (and resulting
poor orbit coverage) determines their grade. Others have shorter periods, thus good
coverage, but are close and difficult to measure, yielding large separation residuals.
Simple polynomial fits were made between each set of means and their corresponding grades,
and the best fit to the Fourth Catalog grades was found by averaging results for
the number of observations, the number of revolutions, the maximum angle and phase gaps,
and the weighted rms separation residual. New grades were then calculated for each of the
901 orbits based on all these factors; Figure 5 illustrates the degree of correlation
between our new, "objective" grades and the Fourth Catalog originals. Some 98% of
the grades matched to within one grade level. A check of those systems where our grades
disagreed by more than 1 grade found that in nearly all cases the Fourth Catalog
grades appeared to be in error. It therefore appears that our quantitative method for
grading orbits gives a reasonably good match to Worley & Heintz' originals.
Figure 5: Comparison of grades determined by the method described here with those
determined by Worley & Heintz. Circle sizes are scaled to the corresponding number of
orbits with these grades; the numbers themselves are given inside all but the smallest
circles, where N is only 1 or 2.
One last adjustment was made before grades were determined for all orbits. Thanks to the
higher astrometric accuracy achievable by interferometric techniques, we now have the
ability to determine orbital elements with higher accuracy than previously considered
possible. Since an old "grade 1" orbit may no longer be considered definitive, we
have applied a "grade deflation" factor by modifying our polynomial fits somewhat. The
factors we applied are as follows:
old grade 1 --> new grade 1.4
old grade 2 --> new grade 2.3
old grade 3 --> new grade 3.2
old grade 4 --> new grade 4.1
old grade 5 --> new grade 5.0
It is worth noting that combined astrometric/spectroscopic solutions are graded only on
the number, quality, and distribution of their differential astrometric measures. These
solutions typically have P, T, e, and w (or at least a subset
of these elements) known to higher accuracy than is reflected in only the visual data.
A handful of orbits could not be graded, due to a lack of rho and theta
measures in the WDS. The first class of these are the few interferometric binaries
observed by the Mark III or the Palomar Testbed Interferometer (c.f., Boden et al. 1999)
for whom only visibilities were published. These orbits, given a grade of "8" in the
catalog, are usually of quite high quality. More common are astrometric orbits, which
receive a grade of "9"; these orbits tend to give rather poor fits to any later resolved
A final note: we do not consider this grading method optimum; a visual inspection of
competing orbits is still necessary if their grades are within a few tenths of each other.
Other schemes, such as the "efficiency" technique of Eichhorn (c.f., Eichhorn & Cole
1985), will be investigated in the future. For the present, however, we think this method
gives reasonably reliable results.
(Note: All observer weights were reevaluated in March 2004, and all orbits were
regraded and new figures generated on a regular basis to reflect measures recently added
to the WDS. The reevaulation weights led to minor changes for most orbits - typically 0.0
to 0.2 grades - but the inclusion of new data has occasionally resulted in major revisions
of grades for individual systems, as might be expected.)
DESCRIPTION OF THE CATALOG
The "master file" for the Sixth Catalog includes all sets of orbital elements in
the Fourth Catalog, as well as all subsequently published orbits either tabulated
by Worley or found through searches of the literature from 1980 through the present.
Several older catalogs, including those of See (1898), Lewis (1906), and Finsen & Worley
(1970) have been added for historical purposes; others are being incorporated as time
permits. This file included 7,921 orbits of 2,516 systems as of 8 June 2015. All orbits
are graded, and only those judged of highest grade for each system are included in the
published Sixth Catalog. If two orbits for a given system are judged to be of
nearly identical quality, the earlier-published orbit is usually chosen for the catalog
(unless the later orbit also includes formal errors to the elements). A few systems are found to
have two very different sets of orbital elements which yield comparable grades; in these
cases both orbits are included. These "special cases" bring the total number of orbits
in the current Sixth Catalog to 2,620.
Names and orbital elements for a given system are tabulated on two lines, with a blank
line separating each orbit for ease in reading. A text version of the catalog (one line
per orbit) is also available, as described in the format description page. Columns in the
main catalog are as follows:
- Epoch-2000 coordinates, usually given to 0.01s accuracy in right ascension and 0.1" in
declination. Most coordinates were extracted from the Tycho-2 catalog.
- Washington Double Star (WDS) designation. Many of these coordinates (given to 0.1m
and 1') were generated by precessing lower precision B1900 positions to J2000;
therefore the WDS designations may vary slightly from the coordinates in column 1.
- Discoverer designation and components involved. If no components are listed, the
orbit is of the AB pair.
- HD (Henry Draper catalog) number.
- Magnitude of the primary component. Codes ">" and "<" preceding the magnitude
indicate the value is an upper or lower limit. Codes "v" or "k" following the value
indicates a star of variable magnitude or a K-band magnitude.
- The period (P), followed by code indicating units:
"c" = centuries,
"d" = days,
"h" = hours,
"m" = minutes,
"y" = years.
- The semi-major axis (a), followed by code indicating units:
"a" = arcseconds,
"m" = milliarcseconds,
"u" = microarcseconds.
- The inclination (i), in degrees.
- The node (Omega), in degrees. An identified ascending node is indicated by an
asterisk following the value.
- The time of periastron passage (T), followed by code indicating units:
"d" = Julian date, with first two digits truncated (i.e., JD-2400000),
"m" = modified Julian date (JD-2400000.5),
"y" = fractional Besselian year.
- The eccentricity (e).
- The longitude of periastron (w), in degrees, reckoned from the node as listed.
- Equinox, if any, to which the node refers.
- The grade (to nearest integer), as previously discussed.
- A link "N" to any notes for this system.
- 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.
- A link "E" to appropriate entries in the ephemeris file.
- 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.
Columns in the ephemeris file are as follows:
- ADS (Aitken Double Star catalog) number.
- Hipparcos number.
- Magnitude of the secondary component. Codes are as described for the primary.
- Published formal errors in P. Units are the same as for P.
- Published formal errors in a. Units are the same as for i.
- Published formal errors in i.
- Published formal errors in Omega.
- Published formal errors in T. Units are the same as for T.
- Published formal errors in e.
- Published formal errors in w.
- The date of the last observation used in the orbit calculation, when given.
- The WDS designation, as above.
- The discoverer designation, as above.
- The orbit grade, as above.
- The reference code, as above.
- Predicted values of theta and rho for the years 2005-2009.
A subset of systems from the Sixth Catalog was prepared in answer to requests for
lists of binaries which might be used for scale calibration purposes. Stars initially
picked for this list included most of the "grade 1" orbits; these are systems having many
observations (usually covering more than one orbital revolution), good phase coverage,
and small separation residuals. These tend to be closer, shorter-period systems, in some
cases resolvable only by large telescopes or multi-aperture interferometers. In order to
provide calibrators for smaller instruments, a similar number of wider, long-period
systems were chosen as well. Orbital coverage for these wide systems is incomplete, so
most were given grades of only 4 or 5; however, since orbital motion is slow, the quoted
elements should predict the stars' motions quite well for many years into the future.
This subset of the Sixth Catalog presently includes 81 orbits of 80 systems. As in
the main catalog, figures are included in order to allow the user to visually inspect each
orbit's quality prior to use. An expanded set of ephemerides has also been generated,
giving predicted separations and position angles with finer time resolution than in the
main catalog (although these ephemerides will obviously still be of little use for very
Note that all "calibration candidate" orbits are not of the same quality. Before
adopting a set of elements it is recommended that users examine the elements, figures,
etc. carefully to check whether that orbit appears to be of proper scale and sufficient
quality for their purposes. Also, using measurements of double stars to calibrate the
measurement of other double stars is certainly circular (or, if you will, Keplerian). We
strongly advocate the use of other absolute calibration techniques such as a slit mask
(cf., McAlister et al. 1987, Hartkopf et al. 1997, Douglass et al. 1997) or at least
star trails (for east-west orientation) if at all possible. When double stars are
necessary for scale calibration, the set provided should be adequate; however, the
measures determined will only be as accurate as the calibration systems used. The use of
these systems for identification of higher-order motions or submotions is discouraged.
Various statistical comparisons of the Sixth Catalog can be made, both with
earlier orbit catalogs and with itself. Figures 6 and 7 (below) show the distribution of
orbits with grade and period for the current catalog, together with the corresponding
numbers for four earlier catalogs.
Figure 8 (above) shows a plot of log(P) versus e for the orbits in the
Sixth Catalog. The dramatic circularization seen in similar plots for
spectroscopic binaries is not seen in resolved binaries, due to their longer periods.
Finally, Figure 9 (above) is a plot of [Periastron_(outer binary) / Apastron_(inner
binary)] versus |i_(outer binary) - i_(inner binary)| for the twenty hierarchical
systems with visual orbits determined for both hierarchies. Harrington (1992)
quantified a value of 3 for the ratio of periastron(outer binary) to apastron(inner
binary) of the inner binary as the critical factor for long-term stability (assuming
equal mass companions). Hierarchies to the left of the dotted line may demonstrate
long-term instabilities, while those to the right of the dashed line have ratios that
may allow intermediate hierarchies.
Systems which are mildly interacting may show a tendency towards co-planarity, so
the tendency of smaller inclination differences having smaller period ratios is not
surprising. Of the five systems lying between the dotted and dashed lines:
- 02291+6724 = CHR 6Aa + STF 262Aa-B : Both orbits are of grade 5 and the ratio here
- 06003-3102 = HU 1399AB + HJ 3823AB-C : this one is the closest to the line and the
incomplete orbital coverage of the wider system may be the culprit.
- 08592+4803 = HU 628BC + HJ 2477A-BC : the orbit for the wider system is highly
suspect. There seems to be a systematic drift in the O-C values for this
orbit and it may not be even a physical association.
- 23019+4220 = BLA 12Aa + WRH 37Aa-B : The short-period orbit is based on only five
data points (one of those with a large residual) and needs more data.
- 23393+4543 = CHR 149Aa + 3A 643Aa-B : Also suffering from a paucity of data, the
short-period system here has four differential measures and needs more data, too.
Thanks foremost to the U.S. Naval Observatory for five decades' worth of support for
the USNO double star observing program and the Washington Double Star Catalog and related
products. Thanks also to the late Drs. Wulff Heintz and William Finsen, without whose
efforts this series of catalogs would never have existed. This catalog has made use of
the SIMBAD database.
We dedicate this catalog to the memory of Charles Edmund Worley, our colleague and friend.
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