Note: As of January 2018, the Fourth Interferometric Catalog will no longer be maintained. This change, after 35+ years, is due to staffing limitations at USNO (primarily the retirement of WIH). Over the coming months, the observations of single stars / never-resolved pairs will be copied to a new WDS "single-star supplement", whose format will be similar to that of the WDSS. All measures of resolved pairs will be copied to the main WDS catalog as needed. Preliminary versions of the "WDSSSS" will be posted; your comments and suggestions regarding content, format, etc. will be welcome, as always.

The following description is adapted from a paper by Hartkopf et al. (2001, AJ, 122, 3480.)

The Fourth Catalog of Interferometric Measurements of Binary Stars includes all published measures of binary and multiple star systems obtained by high-resolution techniques (speckle interferometry, photoelectric occultation timings, etc.), as well as negative examinations for duplicity. A brief summary and statistical analysis of the contents of the catalog follow.

The Fourth Catalog of Interferometric Measurements of Binary Stars began in 1982 as an internal database at the Georgia State University Center for High Angular Resolution Astronomy (CHARA), tabulating binary star observations made using the technique of speckle interferometry by that group's speckle camera. The Speckle Catalog soon grew to encompass other published speckle efforts, then all published astrometric and photometric data for binary stars (and single stars observed in duplicity surveys) obtained by other high angular resolution techniques (lunar occultations, adaptive optics, eyepiece interferometry, Hipparcos, etc.) as well. This extended the catalog's baseline of observations back by nearly a century, to the efforts of Schwarzschild & Villiger (1896). Results of surveys based on various infrared speckle or imaging techniques were later added, as well, even though some of these don't really qualify as high resolution.

Two printed editions of the catalog were published in the 1980's (McAlister & Hartkopf 1984, 1988), and web versions have been available since the early 1990's (Hartkopf et al. 2001a, 2001b). After the speckle efforts at CHARA were suspended in the late 1990's (in order to devote more resources to their long-baseline interferometry project) one of the authors (WIH) transferred the catalog (still nicknamed the Speckle Catalog in honor of its origins) to the U.S. Naval Observatory, whose own speckle efforts had begun earlier in the decade.

Although the catalog is updated regularly, statistics are updated on only an occasional basis. The table below summarizes the contents of the catalog as of 9 January 2018. In addition to the astrometric totals presented here, the catalog includes 73,894 observations of photometric data only. Figures 1 - 3 illustrate the distribution of catalog data with time, separation, and declination, respectively.

      ------------------------------------------------------------------

      Fourth Interferometric Catalogue Statistics (as of 09 January 2018)
    
             Number of resolved stars:                      66,225
	     Number of never-resolved stars:                27,330
             Total number of stars:                         93,555 
             Median separation                               0".89


        Breakdown of data by method:             
                                          resolved  unresolved   total

            Tycho                          40,871      1,001     41,872 
            Hipparcos                      13,880     16,798     30,678   
            USNO Speckle                   22,294      4,758     27,052                        
            CHARA Speckle                  18,527      6,479     25,006  
            Other speckle, AO, etc         31,686     14,466     46,152   
            Eyepiece interferometry         3,085        700      3,785   
            Occultation                     1,825        770      2,595   
            Multi-aperture interferometers  3,276      1,053      4,329   
            Hubble                          2,040      3,638      5,678   
            Other techniques               25,582     43,126     68,708
           -------------------------------------------------------------
            TOTAL                         163,066     92,789    255,855


        Of the resolved total, 2,473 are vector separations (from either
        occultations or one-dimensional IR speckle). 

      ------------------------------------------------------------------

The catalog is divided into 24 one-hour right ascension bands, as follows:

The entire catalog is also available in plain text and gzipped plain text versions. Sizes are roughly 44 and 8MB, respectively. Entries for each system are comprised of two parts: an identification line containing designations from various catalogs, followed by individual measures sorted in order of observation date (see the format file). Major changes with this version include coordinates to 0.01s in RA and 0".1 in DEC, improvements in the formatting of filter information to allow longer wavelengths, and the addition of technique codes. The ID line format was changed slightly in July 2007 to allow additional space for long names (e.g., 2MASS designations).

Each observation includes a reference code linked to a reference file. Similarly, systems having notes are flagged with links to a notes file. An additional change in July 2007 provided links to the Sixth Orbit Catalog for pairs with published visual or astrometric orbits.

A common notes file is used for all USNO double star catalogs (WDS, plus the Interferometric and Orbit catalogs). As a result, the notes file will include systems in addition to those in this catalog. Also, because the notes file is much larger, it has been divided into 24 smaller files for faster linking to the individual catalog measurements files.

Your comments regarding either style or substance are welcome, as are reports of any errors you run across in the catalog. Please send them via email to the address listed on our contact page, and include in the subject line: "CRF WDS Comments" in the subject line to ensure it is properly routed. 

• Anderson, J.A. 1920, ApJ 51, 263
• Hartkopf, W.I., Mason, B.D., McAlister, H.A., Turner, N.H., Barry, D.J., Franz, O.G., & Prieto, C.M. 1996 AJ, 111, 936
• Hartkopf, W.I., McAlister, H.A. & Mason, B.D. 2001a, Third Catalog of Interferometric Measurements of Binary Stars, CHARA Contrib. No. 4
• Hartkopf, W.I., Mason, B.D., Wycoff, G.L., & McAlister, H.A. 2001b, Fourth Catalog of Interferometric Measurements of Binary Stars
• Horch, E.P., Franz, O.G., & Ninkov, Z. 2000, AJ 120, 2638
• McAlister, H.A. & Hartkopf, W.I. 1984, Catalog of Interferometric Measurements of Binary Stars, CHARA Contrib. No. 1
• McAlister, H.A. & Hartkopf, W.I. 1988, Second Catalog of Interferometric Measurements of Binary Stars, CHARA Contrib. No. 2
• Merrill, P.W. 1922, ApJ 56, 40
• Schwarzschild, K. & Villiger, W. 1896, Astr. Nach. 139, 353