The GB6 Catalog of Radio Sources

The Green Bank 4.85 GHz northern sky survey was made with the (former) 91 m telescope during November 1986 and October 1987. The final set of images covering the declination band from 0 to +75 deg was constructed with data from both epochs. Its noise and position errors are nearly a factor of sqrt(2) smaller than in the epoch 1987 images, from which the 87GB catalog of 54,579 sources stronger than S ~ 25 mJy was extracted. The new images were used to make the GB6 Catalog (Gregory, P. C., Scott, W. K., Douglas, K., & Condon, J. J. 1996, ApJS, 103, 427) of 75,162 discrete sources with angular sizes < 10.5 arcmin and flux densities above S ~ 18 mJy at 6 cm wavelength. This catalog is available in machine-readable versions with either B1950 or J2000 positions and as a printed book with peak flux densities and B1950 positions only.


Getting the GB6 catalog by anonymous FTP

The GB6 catalog is available in compressed or uncompressed digital versions with either B1950 or J2000 positions. The machine-readable catalogs can be obtained by anonymous FTP as shown below:

     ftp nvss.cv.nrao.edu
     login: anonymous
     password:             (type your full email address here)
     cd pub/gb6            (to access the GB6 catalog directory)
     ls                    (to list the directory contents)
     get README            (to get a copy of the README file)
     get J2000             (to get the uncompressed catalog (6 Mbyte)
                            with J2000 coordinates)
     binary                (to copy binary files)
     get B1950.gz          (to get the compressed catalog (2 Mbyte)
                            with B1950 coordinates)
     quit

Compression: The catalogs are stored as plain text files compressed in GNU zip (gzip) format, the .gz extension denoting this compression. If an uncompressed version is desired, omit the .gz when requesting the file. Gzipped files may be uncompressed with the command gunzip which is available for most computer systems. Get the text file pub/nvss/compress.txt for a more detailed description of gzip.


Format of the GB6 catalog

The digital catalog format is illustrated by the first source in the B1950 list, GB6 0000+1833:

0.........1.........2.........3.........4.........5.........6.........7........
1234567890123456789012345678901234567890123456789012345678901234567890123456789

000004.7 0.7 +183324 11 -42.5 107.2    64    7      1.06 0.94  79   0  937  388

Bytes (01--02).--- Hours of right ascension, format I2
Bytes (03--04).--- Minutes of right ascension, format I2
Bytes (05--08).--- Seconds of right ascension, format F4.1
Bytes (09--12).--- RMS uncertainty in right ascension (s), format F4.1
Byte  (14).    --- Sign of declination, format A1
Bytes (15--16).--- Degrees of declination, format I2
Bytes (17--18).--- Arcminutes of declination, format I2
Bytes (19--20).--- Arcseconds of declination, format I2
Bytes (22--23).--- RMS uncertainty in declination (arcsec), format I2
Bytes (25--29).--- Galactic latitude (deg), format F5.1
Bytes (31--35).--- Galactic longitude (deg), format F5.1
Bytes (37--41).--- 4.85 GHz peak flux density (mJy), format I5
Bytes (43--46).--- RMS uncertainty in peak flux density (mJy), format I4
Byte  (49).    --- Flag "E" for significant extension, format A1
Byte  (50).    --- Flag "W" for warning, format A1
Byte  (51).    --- Flag "C" for confusion, format A1
Bytes (53--56).--- Normalized FWHM major axis, format F4.2
Bytes (58--61).--- Normalized FWHM minor axis, format F4.2
Bytes (63--65).--- Fitted major-axis position angle (deg east of north),
                   format I3
Bytes (67--69).--- Local sky level (mJy), format I3
Bytes (71--74).--- Map pixel column number counted from left, format I4
Bytes (76--79).--- Map pixel row number counted from bottom, format I4


If you would like to order the printed catalog or have any questions, comments, or special requests, please contact:

jcondon@nrao.edu